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Natural Resources Conservation Service

SSM - Ch. 3. Examination and Description of Soil Profiles

Revised by Soil Science Division Staff.
 

Quick Links

Introduction
General Terms Used to Describe Soils
Studying Pedons
Designations for Horizons and Layers
Near Surface Subzones
Root-Restricting Depth
Particle-Size Distribution
Soil Texture
Rock Fragments and Pararock Fragments
Artifacts
Compound Texture Modifiers
Fragments on the Surface
Soil Color
Soil Structure
Internal Ped and Void Surface Features
Concentrations
Pedogenic Carbonates
Redoximorphic Features
Consistence
Roots
Pores
Animals
Selected Chemical Properties
Soil Water
Soil Temperature
References
 

Introduction

A description of the soils is essential in any soil survey. This chapter provides standards and guidelines for describing the soil. It contains standard technical terms and their definitions for most soil properties and features and provides information for describing the necessary related facts. For some soils, standard terms are not adequate and must be supplemented by a narrative. Some soil properties change through time. Many properties must be observed over time and summarized if one is to fully understand the soil being described and its response to short-term environmental changes. Examples are the length of time that cracks remain open, the patterns of soil temperature and moisture, and the variations in size, shape, and hardness of clods in the surface layer of tilled soils.

This chapter does not discuss every possible soil property. For some soils, other properties need to be described. Good judgment is needed to decide what properties merit detailed attention for any given pedon (sampling unit). Observations must not be limited by preconceived ideas about what is important.

Although the format of the description and the order in which individual properties are described are less important than the content of the description, a standard format has distinct advantages. The reader can find information more rapidly, and the writer is less likely to omit important features. Furthermore, a standard format makes data entry into a computer database more efficient. Any standardized forms need to allow enough space for all possible information.

Each investigation of the internal properties of a soil is made on a soil body with certain dimensions. The body may be larger than a pedon (e.g., a backhoe pit) or represent only a portion of a pedon (e.g., a sample from a hand auger). During field operations, many soils are investigated by examining the soil material removed by a sampling tube or auger. For rapid investigations of thin soils, a small pit can be dug and a section of soil removed with a spade. All of these are samples of pedons. Knowledge of the internal properties of a soil is derived mainly from studies of such samples. Samples can be studied more rapidly than entire pedons; consequently, a much larger number can be studied and for several more places. For many soils, the information obtained from a small sample amply describes the pedon from which it is taken. For other soils, however, important properties of a pedon are not observable in a smaller sample and detailed studies of the entire pedon are needed. Complete study of an entire pedon requires the exposure of a vertical section and the removal of horizontal sections layer by layer. Horizons are studied in both horizontal and vertical dimensions. The kind of exposure (e.g., bucket auger, push tube, small hand-dug pit, backhoe pit, road cut, etc.) should be identified in the soil description.

The information in this chapter, which focuses on the standards and guidelines for describing a soil profile in the field, is complemented by that provided in chapters 2, 6, 10, and Chapter 2 provides information related to describing the site surrounding the soil profile. Chapter 6 discusses the use of proximal sensors to measure some soil properties quickly and efficiently at field and larger scales by using field-based electronic technology. Chapter 10 provides information specific to describing subaqueous soils. Chapter 11 discusses soils heavily impacted by human activity.
 

General Terms Used to Describe Soils

This section describes several of the general terms for internal elements of the soil. Other more specific terms are described or defined in the following sections.

Pedon

A pedon is a three-dimensional body of soil that has sufficient area (roughly 1 to 10 m2) and depth (up to cm) to be used in describing the internal arrangement of horizons and in collecting representative samples for laboratory analysis (see chapter 4). The pedon is the individual classified with Soil Taxonomy. Multiple pedons that have the same classification and occur together in landscapes are used in defining soil series. Conceptually, these contiguous pedons are called polypedons (see chapter 4).

Soil Profile

A soil profile is smaller than a pedon. It is exposed by a two-dimensional vertical cut through the soil. It is commonly conceived as a plane at right angles to the soil surface. In practice, a description of a soil profile includes soil properties that can be determined only by inspecting volumes of soil. However, the volume of soil described from a profile is almost always less than the volume of soil defined by a full pedon because observations of the soil profile are generally made to only a few decimeters behind the face of the exposed profile. A pedon description is commonly based on examination of a profile, and the properties of the pedon are inferred from the properties of the profile. The width of a profile ranges from a few decimeters to several meters or more. The size of the profile should be sufficient to include the largest structural units.

Soil Horizon

A soil horizon is a layer, approximately parallel to the surface of the soil, that is distinguishable from adjacent layers by a distinctive set of properties produced by the soil-forming processes (i.e., pedogenesis). The term “layer” is used instead of “horizon” if the properties are inherited from the parent material, such as sedimentary strata. Horizons, in contrast, display the effects of pedogenesis, such as the obliteration of sedimentary strata and accumulation of illuvial clay.

Solum

The solum (plural, sola) of a soil consists of a set of horizons that are related through the same period of pedogenesis. It includes all horizons now forming. It may also include a bisequum (discussed below). It does not include a buried soil or layer unless it has acquired some of its properties by currently active soil-forming processes. The solum of a soil is not necessarily confined to the zone of major biological activity. Its genetic horizons may be expressed faintly to prominently. A solum does not have a maximum or minimum thickness.

Solum and soils are not synonymous. Some soils include layers that are not affected by soil formation. These layers are not part of the solum. The number of genetic horizons ranges from one to many. An A horizon that is 10 cm thick overlying bedrock is by itself the solum. A soil that consists only of recently deposited new soil material or recently exposed soft sediment generally does not have a solum.

In terms of soil horizons as described in this chapter, a solum consists of O, V, A, E, and B horizons and their transitional horizons. Included are horizons with an accumulation of carbonates or more soluble salts if these horizons are either within, or contiguous to, other genetic horizons and are judged to be at least partly produced during the same period of soil formation.

The lower limit of the solum, in a general sense, in many soils should be related to the depth of rooting for perennial plants, assuming that water state and chemistry are not limiting. In some soils, the lower limit can be set only arbitrarily and is defined in relation to the particular soil. For example, horizons of carbonate accumulation are easily visualized as part of the solum in many soils in arid and semiarid environments. However, to conceive of cemented horizons of carbonates that may extend for 5 meters or more below the surface as part of the modern solum is more difficult. Such massive carbonate horizons represent pedogenesis over hundreds of thousands of years and are referred to as relict paleosols. Gleyed soil material begins in some soils a few centimeters below the surface and continues practically unchanged to a depth of many meters. Gleying immediately below the A horizon is likely to be related to the processes of soil formation in the modern soil. At great depth, gleying is likely to be relict or related to processes that are more geological than pedological. The same kind of problem exists for some deeply weathered soils—the deepest material penetrated by roots is very similar to the weathered material at much greater depth.

For some soils, digging deep enough to reveal all of the relationships between soils and plants is not practical. Plant roots, for example, may derive much of their moisture from fractured bedrock. Descriptions should indicate the nature of the soil-rock contact and determinations about the upper part of the underlying rock.

Not everyone will agree about the exact extent of the solum in some soils. For example, a certain level of subjectivity is involved in differentiating transitional BC or CB horizons from C horizons or in determining which properties observed in the soil are the product of active pedogenic processes. The concept of the solum remains useful for discussions about the nature of soils and soil profiles but is generally not used as a part of any technical definitions.

Sequum

A sequum (plural, sequa) consists of a B horizon and any overlying eluvial horizons. A single sequum is considered to be the product of a specific combination of soil-forming processes.

Most soils have only one sequum, but some have two or more. For example, a new sequence of horizons that meet the criteria for a Spodosol can form in the upper part of a previously existing Alfisol, producing an eluviated zone and a spodic horizon underlain by another eluviated zone overlying an argillic horizon. Such a soil has two sequa. Soils in which two sequa have formed, one above the other in the same deposit, are said to be bisequal.

If two sequa formed in different deposits at different times, the soil is not bisequal. For example, a soil having an A-E-B horizon sequence may form in material that was deposited over another soil that already had an A-E-B horizon sequence. Each set of A-E-B horizons is a sequum, but the combination is not a bisequum; the lower set is a buried soil. If the horizons of the upper sequum extend into the underlying sequum, the affected layer is considered part of the upper sequum. For example, the A horizon of the lower soil may retain some of its original characteristics and also have some characteristics of the overlying soil. In this case, the soils are also not considered bisequal; the upper part of the lower soil is the parent material of the lower part of the currently forming soil. In many soils the distinction cannot be made with certainty. If some of the C material of the upper sequum remains, the distinction is clear.
 

Studying Pedons

Site Selection

Pedons representative of an extensive mappable area are generally more useful than pedons that represent a transitional area to another soil. For detailed study of a soil, a pedon is tentatively selected and then examined preliminarily to determine whether or not it represents the desired segment of the soil’s range. This is a critical step. Typically, only a few pedons can be studied in detail due to the time and expense involved in exposing, describing, photographing, and sampling soil profiles and performing necessary laboratory analysis. It is very important that the site selected for study is a representative sample of the overall soil body in the landscape because data from the site will be used to classify the soil pedon and correlate it with other similar pedons.

Information Recorded

For a soil description to be of greatest value, detailed information about its setting should be recorded (see chapter 2). Important items include location (identified by latitude and longitude, including datum, or another acceptable geographic location system), the part of the landscape that the pedon represents (i.e., landform, position on landform, any applicable microfeature), elevation, aspect, parent material, vegetation, land use, and erosion or other disturbance affecting the soil profile. The level of detail will depend on the objectives. A complete setting description should include information about the pedon and other soils conterminous with the pedon. It also may include information on any features that differ from the central concept of the soil series for which the described pedon is named (if a series has been defined).

The description of a body of soil in the field, whether an entire pedon or a soil profile within it, should record the kinds of horizons or layers, their depth and thickness, and the properties of each. Generally, external features, such as slope, surface stoniness, erosion, and vegetation, are observed for the area around the pedon, which is considered to be part of the same soil body. Internal features, such as color, texture, and structure, are observed from the study of the pedon.

Observing Pedons

In order to observe a pedon fully, including soil structure (size and kind), horizon boundary topography, and short-range variability in horizon thickness, a pit exposing a vertical face approximately 1 meter across to an appropriate depth (fig. ) is adequate for most soils. Excavations associated with roads, railways, gravel pits, and other soil disturbances provide easy access for studying soils. Old exposures, however, must be used cautiously. In these areas, the soils can dry out or freeze and thaw from both the surface and the sides. In addition, the soil structure may be more pronounced than is typical, salts may have accumulated near the edges of exposures or been removed by seepage, plinthite may have irreversibly hardened to ironstone, or other changes may have taken place.

Figure A shallow soil pit with a face that has been cleaned and prepared for describing the soil profile. This soil (a Fibristel in Alaska) has been dug to the depth of permafrost (about 40 cm).For hand- or backhoe-dug pits, care must be taken to ensure that the pit conforms to safety regulations. Loose sandy soils and wet soils are particularly susceptible to cave-ins.

After the sides of the pit are cleaned of all loose material disturbed by digging, the exposed vertical faces are examined, typically starting at the top and working downward, to identify significant changes in properties. Boundaries between layers are marked on the face of the pit, and the layers are identified and described.

Photographs should be taken after the layers have been identified but before the vertical section is disturbed in the description-writing process. An estimation of the volume of stones or other features also is done before the layers are disturbed.

If bulk samples are to be collected for laboratory analysis, it generally is best to begin with the bottom layer and work upward. This prevents material from the upper layers falling onto the face of lower layers before they have been sampled.

A horizontal view of each horizon is useful. This exposes structural units that otherwise may not be readily observable from the vertical pit face. Patterns of color within structural units, variations of particle size from the outside to the inside of structural units, and the pattern in which roots penetrate structural units are commonly seen more clearly in a horizontal section (fig. ).

Figure A horizontal view (looking down) of a fragipan from a soil (a Fragiudalf) in Tennessee.

Measuring Depth to and Thickness of Horizons and Layers

Soil Surface

When describing soil profiles, depth is measured from the soil surface. Generally, the soil surface is the top of the mineral soil. For soils with an O horizon (Oi, Oe, or Oa), it is the top of the O horizon. Fresh leaf or needle fall that has not undergone observable decomposition is excluded from the concept of an O horizon and may be described separately as a surface feature. Profile measurements begin below any fresh leaf or needle fall.

For soils that have a cover of 80 percent or more rock or pararock fragments (as in some areas of rubbly colluvial materials), the top of the soil is considered the mean height of the tops of the rock or pararock fragments. Depth measurements are taken from this height.

It is important to note that, when measuring depth and thickness for taxonomic purposes, the “mineral soil surface” is commonly specified as the datum to use in measurements. This essentially excludes any overlying O horizon and is therefore not synonymous with the soil surface as defined here for making soil descriptions. See Keys to Soil Taxonomy (Soil Survey Staff, b or later version) for further information.

Depth Measurements

The depth to a horizon or layer boundary commonly differs within short distances, even within a pedon. The part of the pedon that is typical or most common is described. In the soil description, the horizon or layer designation is listed, followed by the values that represent the depths from the soil surface to the upper and lower boundaries (e.g., Bt1 - 8 to 20 cm). The depth to the lower boundary of a horizon or layer is the depth to the upper boundary of the horizon or layer beneath it. Variation in the depths of the boundaries is recorded in the description of the horizon or layer. The depth limits of the deepest horizon or layer described include only that part actually seen.

In some soils, the variations in depths to boundaries are so complex that the usual terms used to describe the boundary topography are inadequate. These variations are described separately, e.g., “depth to the lower boundary is mainly 30 to 40 cm, but tongues extend to depths of 60 to 80 cm.” The lower boundary of a horizon or layer and the upper boundary of the horizon or layer below share a common irregularity.

Thickness Measurements

The thickness of each horizon or layer is the vertical distance between the upper and lower boundaries. Overall thickness may vary within a pedon, and this variation should be noted in the description. A range in thickness may be given, e.g., “thickness ranges from 20 to 30 cm.” This range is not calculated from the range of upper and lower boundary depths. Instead, the range is calculated from evaluations across the exposure at different lateral points. For example, the upper boundary of a horizon may range in depth from 25 to 45 cm and the lower boundary from 50 to 75 cm. Taking the extremes of these two ranges, it is incorrect to conclude that the horizon thickness ranges from as little as 5 cm to as much as 50 cm when in fact it may be 20 to 30 cm in the field.
 

Designations for Horizons and Layers

Soils vary widely in the degree to which horizons are expressed. Relatively fresh parent materials, such as recent deposits of alluvium, eolian sands, or mantles of volcanic ash, may have no recognizable genetic horizons but may have distinct layers that reflect different modes of deposition. As soil formation proceeds, horizons in their early stages may be detected only by very careful examination. As horizons increase in age, they generally are more easily identified in the field. However, only one or two different horizons may be readily apparent in some very old, deeply weathered soils in tropical areas where annual precipitation is high. This section provides the standard nomenclature and definitions for a system used to assign symbols to soil horizons and layers.

Background and Concepts for Use of Designations

Different kinds of layers are identified by different symbols. Designations are provided for layers that have been changed by soil formation and for those that have not. Each horizon designation indicates either that the original material has been changed in certain ways or that there has been little or no change. The designation is assigned after comparison of the observed properties of the layer with properties inferred for the material before it was affected by soil formation. The processes that have caused the change need not be known; properties of soils relative to those of an estimated parent material are the criteria for judgment. The parent material inferred for the horizon in question, not the material below the solum, is used as the basis of comparison. The inferred parent material commonly is very similar to, or the same as, the soil material below the solum.

Designations show the describer’s interpretations of genetic relationships among the layers within a soil. Layers do not need to be identified by symbols in order to make a good description, but the usefulness of soil descriptions is greatly enhanced by the proper use of designations. The designations provide a sort of shorthand nomenclature conveying the important properties observed by the person describing the soil as well as the genetic inferences made by that person regarding the formation of the soil. The definitions of the symbols provided below are generally more qualitative than quantitative. There is a small degree of subjectivity that allows some freedom for the describer to convey their theory of how the soil formed. There may be a certain level of inconsistency in the way different describers label the horizons of the same profile. For example, one describer may label a horizon “C” while another may label it “CB” or one may record a subtle lithologic discontinuity that another person does not observe.

Designations are not substitutes for descriptions. If both designations and adequate descriptions of a soil are provided, the reader has the interpretation made by the person who described the soil and also the evidence on which the interpretation was based.

Genetic horizons are not equivalent to the diagnostic horizons of Soil Taxonomy. Designations of genetic horizons express a qualitative judgment about the kind of changes that are believed to have taken place. Diagnostic horizons are quantitatively defined features used to differentiate taxa. Changes implied by genetic horizon designations may not be large enough to justify recognition of diagnostic criteria. For example, the designation “Bt” does not always indicate an argillic horizon. Furthermore, the diagnostic horizons may not be coextensive with genetic horizons.

Basic System of Horizon and Layer Designations

Four kinds of symbols are used in various combinations to designate horizons and layers:

Capital letters.—Used to designate the master horizons and layers.
Lowercase letters.—Used as suffixes to indicate specific characteristics of master horizons and layers.
Numbers.—Used both as suffixes to indicate vertical subdivisions within a horizon or layer and as prefixes to indicate discontinuities.
Special symbols.—Used to indicate layers formed in human-transported material or sequences of horizons having otherwise identical designations.

Master Horizons and Layers

The capital letters O, L, V, A, E, B, C, R, M, and W represent the master horizons and layers of soils. These letters are the base symbols to which other characters are added to complete the designations. Most horizons and layers have a designation using one capital letter symbol; some have two.

O Horizons or Layers

O horizons or layers are dominated by organic soil materials. Some are saturated with water for long periods; some were once saturated but are now artificially drained; and others have never been saturated.

Some O horizons or layers consist of slightly decomposed to highly decomposed litter (such as leaves, needles, twigs, moss, and lichens) that was deposited on the surface of either mineral or organic soils. Others consist of organic materials that were deposited under saturated conditions and have decomposed to varying stages. The mineral fraction of such material constitutes only a small percentage of the volume of the material and generally much less than half of its weight. Some soils consist entirely of materials designated as O horizons or layers.

An O horizon or layer may be at the surface of a mineral soil or, if buried, at any depth below the surface. A horizon formed by illuviation of organic material into a mineral subsoil is not an O horizon, although some horizons that formed in this manner contain a large amount of organic matter. Horizons or layers composed of limnic materials are not designated as O horizons.

L Horizons or Layers

L horizons or layers include both organic and mineral limnic materials that were either:

  1. Deposited in water by precipitation or through the actions of aquatic organisms, such as algae and diatoms; or
  2. Derived from underwater and floating aquatic plants and subsequently modified by aquatic animals.

L horizons or layers include coprogenous earth (sedimentary peat), diatomaceous earth, and marl. They are described only for Histosols (decomposed plant material) and not for mineral soils. They have only the following suffixes: co, di, or ma (described below). They do not have the subordinate distinctions of the other master horizons and layers.

V Horizons

V horizons are mineral horizons that formed at the soil surface or below a layer of rock fragments (e.g., desert pavement), a physical or biological crust, or recently deposited eolian material. They are characterized by the predominance of vesicular pores and have platy, prismatic, or columnar structure.

Porosity in a V horizon may include vughs and collapsed vesicles in addition to the spherical vesicular pores. V horizons formed in eolian material but may be underlain by soil horizons that formed in residuum, alluvium, or other transported materials. Because of their eolian origin, they are typically enriched in particle-size fractions ranging from silt through fine sand. Rarely, the V horizon is massive rather than structured. The structural arrangement of particles and vesicular porosity differentiates this horizon from the loose, unaltered eolian deposits that may occur above it. Underlying B horizons commonly have redder hues than the V horizon and lack vesicular pores (Turk et al., ).

Transitional and combination horizons with V horizon material occur in certain circumstances. Although uncommon, an AV or VA horizon may occur. It is both enriched in organic matter and contains vesicular pores. BV or VB horizons may indicate vesicular horizons that contain clay or carbonate coatings, or other properties of the underlying B horizon. EV or VE transitional horizons may also occur, especially in sodic soils.

Combination horizons of the V horizon with A, B, or E horizons may occur in bioturbated zones, such as shrub islands or areas where surface cover associated with the vesicular horizon (e.g., desert pavement) is patchy. Vesicular pores have been observed to reform quickly after physical disruption (Yonovitz and Drohan, ).

A Horizons

A horizons are mineral horizons that formed at the soil surface or below an O horizon. They exhibit obliteration of all or much of any original rock structure and show one or both of the following:

  1. An accumulation of humified organic matter closely mixed with the mineral fraction and not dominated by properties characteristic of V, E, or B horizons; and/or
  2. Properties resulting from cultivation, pasturing, or similar kinds of disturbance.

If a surface horizon has properties of both A and E horizons but the feature emphasized is an accumulation of humified organic matter, it is designated as an A horizon. Recent alluvial or eolian deposits that retain most of the original rock structure are not considered to be A horizons unless they are cultivated.

E Horizons

E horizons are mineral horizons in which the main feature is the eluvial loss of silicate clay, iron, aluminum, or some combination of these that leaves a concentration of sand and silt particles. They exhibit obliteration of all or much of the original rock structure.

An E horizon is commonly differentiated from an underlying B horizon in the same sequum by a color of higher value or lower chroma (or both), by coarser texture, or by a combination of these properties. In some soils the color of the E horizon is that of the sand and silt particles, but in many soils coatings of iron oxides or other compounds mask the color of the primary particles. An E horizon is most commonly differentiated from an overlying A horizon by its lighter color. It generally contains less organic matter than the A horizon. It is commonly near the soil surface, below an O, V, or A horizon, and above a B horizon. However, the symbol E can be used for eluvial horizons that are at the soil surface, are within or between parts of the B horizon, or extend to depths greater than those of normal observation, if the horizons have resulted from pedogenic processes.

B Horizons

B horizons are mineral horizons that typically formed below an A, V, E, or O horizon. They exhibit obliteration of all or much of the original rock structure and show one or more of the following as evidence of pedogenesis:

  1. Illuvial concentration of silicate clay, iron, aluminum, humus, sesquioxides, carbonates, gypsum, salts more soluble than gypsum, or silica, alone or in combination;
  2. Evidence of the removal, addition, or transformation of carbonates, anhydrite, and/or gypsum;
  3. Residual concentration of oxides, sesquioxides, and silicate clay, alone or in combination;
  4. Coatings of sesquioxides that make the horizon color conspicuously lower in value, higher in chroma, or redder in hue than overlying and underlying horizons, without apparent illuviation of iron;
  5. Alteration that forms silicate clay or liberates oxides, or both, and that forms pedogenic structure if volume changes accompany changes in moisture content;
  6. Brittleness; or
  7. Strong gleying when accompanied by other evidence of pedogenic change.

All of the different kinds of B horizons are, or originally were, subsurface horizons. B horizons include horizons (cemented or not cemented) with illuvial concentrations of carbonates, gypsum, or silica that are the result of pedogenic processes. They are contiguous to other genetic horizons and brittle layers that show other evidence of alteration, such as prismatic structure or illuvial accumulation of clay.

B horizons do not include layers in which clay films coat rock fragments or cover finely stratified unconsolidated sediments, regardless of whether the films formed in place or by illuviation; layers into which carbonates have been illuviated but that are not contiguous to an overlying genetic horizon; and layers with strong gleying but no other pedogenic changes.

C Horizons or Layers

C horizons or layers are mineral horizons or layers, excluding strongly cemented and harder bedrock, that are little affected by pedogenic processes and lack properties of O, A, V, E, B, and L horizons. Their material may be either like or unlike that from which the solum presumably formed. The C horizon may have been modified, even if there is no evidence of pedogenesis.

Included as C layers (and typically designated Cr) are sediment, saprolite, bedrock, and other geologic materials that are moderately cemented or less cemented (see table ). The excavation difficulty of these materials commonly is low or moderate (see table ). In descriptions of soils that formed in material that is already highly weathered, if this material does not meet the requirements of an A, V, E, or B horizon, it is designated by the letter C. Changes are not considered pedogenic if they are not related to the overlying horizons. Some layers that have accumulations of silica, carbonates, gypsum, or more soluble salts are included in C horizons, even if cemented. However, if a cemented layer formed through pedogenic processes, rather than geologic processes (e.g., lithification), it is considered a B horizon.

R Layers

R layers consist of strongly cemented to indurated bedrock. Granite, basalt, quartzite, limestone, and sandstone are examples of bedrock that commonly is cemented enough to be designated by the letter R. The excavation difficulty of these layers commonly exceeds high. The R layer is sufficiently coherent when moist to make hand-digging with a spade impractical, although it may be chipped or scraped. Some R layers can be ripped with heavy power equipment. The bedrock may have fractures, but these are generally too few or too widely spaced to allow root penetration. The fractures may be coated or filled with clay or other material.

M Layers

M layers are root-limiting layers beneath the soil surface consisting of nearly continuous, horizontally oriented, human-manufactured materials. Examples of materials designated by the letter M include geotextile liners, asphalt, concrete, rubber, and plastic, if they occur as continuous, horizontal layers.

W Layers

W layers are used to identify water layers within or beneath the soil (fig. ). They are not merely layers of saturated soil material but rather zones of water between soil layers. The water layer is designated “Wf ” if it is permanently frozen (as in a glacic horizon) and “W” if it is not permanently frozen (as in a floating bog). The designations W and Wf are not used for shallow water, ice, or snow above the soil surface.

Figure A soil (a Glacistel in Alaska) with a permanently frozen ice layer (designated “Wf”) between depths of 60 and cm. (Photo courtesy of John Kelley)

Transitional and Combination Horizons

In some cases a single master horizon designation does not adequately convey information about the layer, such as where the horizon transitions to another layer or where it contains distinct parts from two kinds of master horizons.

Transitional Horizons

Transitional horizons are dominated by properties of one master horizon but have subordinate properties of another. They are designated by two capital-letter symbols, e.g., AB, EB, BE, or BC. The first letter indicates the horizon whose properties dominate the transitional horizon. An AB horizon, for example, has characteristics of both an overlying A horizon and an underlying B horizon, but it is more like the A horizon than the B.

In some cases, a horizon can be designated as transitional even if one of the master horizons to which it transitions is not present. For example, a BE horizon recognized in a truncated soil has properties similar to those of a BE horizon in a soil from which the overlying E horizon has not been removed by erosion. A BC horizon may be recognized even if no underlying C horizon is present: it transitions to assumed parent materials.

Combination Horizons

Combination horizons have two distinct parts that have recognizable properties of the two kinds of master horizons. They are designated by two capital-letter symbols (master horizons) separated by a virgule (/), e.g., E/B, B/E, or B/C. Most of the individual parts of one horizon component are surrounded by the other. The designation may be used even when horizons similar to one or both of the components are not present, provided that the separate components can be recognized in the combination horizon. The first letter indicates the horizon with the greater volume.

Because single sets of designators do not cover all situations, some improvising may be necessary. For example, Lamellic Udipsamments have lamellae that are separated from each other by eluvial layers. It is generally not practical to describe each lamella and eluvial layer as a separate horizon, so the horizons can be combined and the components described separately. The horizon with several lamellae and eluvial layers can be designated as an “E and Bt” horizon. The complete horizon sequence for these soils could be: Ap-Bw-E and Bt1-E and Bt2-C.

Suffix Symbols

Lowercase letters are used as suffixes to designate specific subordinate distinctions within master horizons and layers. The term “accumulation,” which is used in many of the suffix definitions, indicates that the horizon has more of the material in question than is presumed to have been present in the parent material. The use of a suffix symbol is not restricted only to those horizons that meet certain criteria for diagnostic horizons and other criteria as defined in Soil Taxonomy. If there is any evidence of accumulation, a suffix (or suffixes) can be used. The suffix symbols and their meanings follow:

aHighly decomposed organic material

This symbol is used with O horizons to indicate the most highly decomposed organic materials, which have a fiber content of less than 17 percent (by volume) after rubbing.

bBuried genetic horizon

This symbol indicates identifiable buried horizons with major genetic features that developed before burial. Genetic horizons may or may not have formed in the overlying material, which may be either like or unlike the assumed parent material of the buried horizon. This symbol is not used to separate horizons composed of organic soil material (that are forming at the soil surface) from underlying horizons composed of mineral soil material. It may be used in organic soils, but only if they are buried by mineral soil materials.

cConcretions or nodules

This symbol indicates a significant accumulation of concretions or nodules. Cementation is required. The cementing agent commonly is iron, aluminum, manganese, or titanium. It cannot be silica, dolomite, calcite, gypsum, anhydrite, or soluble salts.

coCoprogenous earth

This symbol, used only with L horizons, indicates a limnic layer of coprogenous earth (sedimentary peat).

dPhysical root restriction

This symbol indicates non-cemented, root-restricting layers in naturally occurring or human-made sediments or materials. Examples of natural layers are dense till and some non-cemented shales and siltstones. Examples of human-made dense layers are plowpans and mechanically compacted zones in human-transported material.

diDiatomaceous earth

This symbol, used only with L horizons, indicates a limnic layer of diatomaceous earth.

eOrganic material of intermediate decomposition

This symbol is used with O horizons to indicate organic materials of intermediate decomposition. The fiber content of these materials is 17 to less than 40 percent (by volume) after rubbing.

fFrozen soil or water

This symbol indicates that a horizon or layer contains permanent ice. It is not used for seasonally frozen layers or for dry permafrost.

ffDry permafrost

This symbol indicates a horizon or layer that is continually colder than 0 °C and does not contain enough ice to be cemented by ice. It is not used for horizons or layers that have a temperature warmer than 0 °C at some time during the year.

gStrong gleying

This symbol indicates either that iron has been reduced and removed during soil formation or that saturation with stagnant water has preserved iron in a reduced state. Most of the affected layers have chroma of 2 or less, and many have redox concentrations. The low chroma can represent either the color of reduced iron or the color of the uncoated sand and silt particles from which iron has been removed. The symbol is not used for soil materials of low chroma that have no history of wetness, such as some shales or E horizons. If it is used with B horizons, pedogenic change (e.g., soil structure) in addition to gleying is implied. If no other pedogenic change besides gleying has taken place, the horizon is designated “Cg.”

hIlluvial accumulation of organic matter

This symbol is used with B horizons to indicate the accumulation of illuvial, amorphous, dispersible complexes of organic matter and sesquioxides. The sesquioxide component is dominated by aluminum and is present only in very small quantities. The organo-sesquioxide material coats sand and silt particles. In some horizons these coatings have coalesced, filled pores, and cemented the horizon. The symbol h is also used in combination with the symbol s (e.g., Bhs) if the amount of the sesquioxide component is significant but the value and chroma, moist, of the horizon are 3 or less.

iSlightly decomposed organic material

This symbol is used with O horizons to indicate the least decomposed of the organic materials. The fiber content of these materials is 40 percent or more (by volume) after rubbing.

jAccumulation of jarosite

This symbol indicates an accumulation of jarosite, which is a potassium (ferric) iron hydroxy sulfate mineral, KFe3(SO4)2(OH)6. Jarosite is commonly the product of pyrite that has been exposed to an oxidizing environment. It has hue of Y or yellower and normally has chroma of 6 or more, although chroma as low as 3 or 4 has been reported. It forms in preference to iron (hydr)oxides in active acid sulfate soils at pH of or less and can be stable for long periods of time in post-active acid sulfate soils with higher pH.

jjEvidence of cryoturbation

This symbol indicates evidence of cryoturbation, which includes irregular and broken horizon boundaries, sorted rock fragments, and organic soil materials occurring as bodies and broken layers within and/or between mineral soil layers. The organic bodies and layers are most commonly at the contact between an active layer and the permafrost.

kAccumulation of secondary carbonates

This symbol indicates an accumulation of visible pedogenic calcium carbonate (less than 50 percent, by volume). Carbonate accumulations occur as carbonate filaments, coatings, masses, nodules, disseminated carbonate, or other forms.

kkEngulfment of horizon by secondary carbonates

This symbol indicates major accumulations of pedogenic calcium carbonate. It is used when the soil fabric is plugged with fine grained pedogenic carbonate (50 percent or more, by volume) that occurs as an essentially continuous medium. It corresponds to the Stage III (or higher) plugged horizon of the carbonate morphogenetic stages (Gile et al., ).

mPedogenic cementation

This symbol indicates continuous or nearly continuous pedogenic cementation. It is used only for horizons that are more than 90 percent cemented but may be fractured. The cemented layer is physically root-restrictive. The predominant cementing agent (or the two dominant ones) can be indicated by letter suffixes, singly or in pairs. The horizon suffix kkm (and the less commonly used km) indicates cementation by carbonates; qm, cementation by silica; sm, cementation by iron; yym, cementation by gypsum; kqm, cementation by carbonates and silica; and zm, cementation by salts more soluble than gypsum. The symbol m is not used for permanently frozen layers impregnated by ice.

maMarl

This symbol, used only with L horizons, indicates a limnic layer of marl.

nAccumulation of sodium

This symbol indicates an accumulation of exchangeable sodium.

oResidual accumulation of sesquioxides

This symbol indicates a residual accumulation of sesquioxides.

pTillage or other disturbance

This symbol indicates disturbance of a horizon by mechanical means, pasturing, or similar uses. A disturbed organic horizon is designated “Op.” A disturbed mineral horizon is designated “Ap” even if it is clearly a former E, B, or C horizon.

qAccumulation of silica

This symbol indicates an accumulation of secondary silica.

rWeathered or soft bedrock

This symbol is used with C horizons to indicate layers of bedrock that are moderately cemented or less cemented. Examples are weathered igneous rock and partly consolidated sandstone, siltstone, or shale. The excavation difficulty is low to high.

sIlluvial accumulation of sesquioxides and organic matter

This symbol is used with B horizons to indicate an accumulation of illuvial, amorphous, dispersible complexes of organic matter and sesquioxides, if both the organic matter and sesquioxide components are significant and if either the value or chroma, moist, of the horizon is 4 or more. The symbol is also used in combination with h (e.g., Bhs) if both the organic matter and sesquioxide components are significant and if the value and chroma, moist, are 3 or less.

sePresence of sulfides

This symbol indicates the presence of sulfides in mineral or organic horizons. Horizons with sulfides typically have dark colors (e.g., value of 4 or less, chroma of 2 or less). These horizons typically form in soils associated with coastal environments that are permanently saturated or submerged (i.e., tidal marshes or estuaries). Soil materials which have sulfidization actively occurring emanate hydrogen sulfide gas, which is detectable by its odor (Fanning and Fanning, ; Fanning et al., ). Sulfides may also occur in upland environments that have a source of sulfur. Soils in such environments are commonly of geologic origin and may not have a hydrogen sulfide odor. Examples include soils that formed in parent materials derived from coal deposits, such as lignite, or soils that formed in coastal plain deposits, such as glauconite, that have not been oxidized because of thick layers of overburden.

ssPresence of slickensides

This symbol indicates the presence of pedogenic slickensides. Slickensides result directly from the swelling of clay minerals and shear failure, commonly at angles of 20 to 60 degrees above horizontal. They are indicators that other vertic characteristics, such as wedge-shaped peds and surface cracks, may be present.

tAccumulation of silicate clay

This symbol indicates an accumulation of silicate clay that either has formed within a horizon and subsequently has been translocated within the horizon or that has been moved into the horizon by illuviation, or both. At least some part of the horizon shows evidence of clay accumulation, either as coatings on surfaces of peds or in pores, as lamellae, or as bridges between mineral grains.

uPresence of human-manufactured materials (artifacts)

This symbol indicates the presence of objects or materials that have been created or modified by humans, typically for a practical purpose in habitation, manufacturing, excavation, or construction activities. Examples of artifacts are bitumen (asphalt), boiler slag, bottom ash, brick, cardboard, carpet, cloth, coal combustion by-products, concrete (detached pieces), debitage (i.e., stone tool flakes), fly ash, glass, metal, paper, plasterboard, plastic, potsherd, rubber, treated wood, and untreated wood products.

vPlinthite

This symbol is used to indicate the presence of iron-rich, humus-poor, reddish material that is firm or very firm when moist and is less than strongly cemented. Plinthite hardens irreversibly when exposed to the atmosphere and to repeated wetting and drying.

wDevelopment of color or structure

This symbol is used only with B horizons to indicate the development of color or structure, or both, with little or no apparent illuvial accumulation of material. Note: It is not used to indicate a transitional horizon.

xFragipan character

This symbol indicates a genetically developed layer that has a combination of firmness and brittleness and commonly a higher bulk density than adjacent layers. Some part of the layer is physically root-restrictive.

yAccumulation of gypsum

This symbol indicates an accumulation of gypsum. It is used when the horizon fabric is dominated by soil particles or minerals other than gypsum. Gypsum is present in amounts that do not significantly obscure or disrupt other features of the horizon. This symbol is also used to indicate the presence of anhydrite.

yyDominance of horizon by gypsum

This symbol indicates a horizon that is dominated by the presence of gypsum. The gypsum content may be due to an accumulation of secondary gypsum, the transformation of primary gypsum inherited from parent material, or other processes. This symbol is used when the horizon fabric has such an abundance of gypsum (generally 50 percent or more, by volume) that pedogenic and/or lithologic features are obscured or disrupted by growth of gypsum crystals. Horizons that have this suffix typically are highly whitened (e.g., value of 7 through and chroma of 4 or less). This symbol is also used to connote the presence of anhydrite.

zAccumulation of salts more soluble than gypsum

This symbol indicates an accumulation of salts that are more soluble than gypsum.

Conventions for Using Horizon Designation Symbols

The following guidelines can be used in assigning horizon designation symbols to soil horizons and layers.

Letter Suffixes

Many master horizons and layers that are symbolized by a single capital letter can have one or more lowercase-letter suffixes. The following rules apply:

  1. Letter suffixes directly follow the capital letter of the master horizon or layer, or the prime symbol, if used.
  2. More than three suffixes are rarely used.
  3. If more than one suffix is needed, the following letters (if used) are written first: a, d, e, h, i, r, s, t, and w. None of these letters are used in combination for a single horizon, except to designate a Bhs horizon or Crt layer.
  4. If more than one suffix is needed and the horizon is not buried, the following symbols, if used, are written last: c, f, g, m, v, and x. Examples are Bjc and Bkkm. If any of these suffixes are used together in the same horizon, symbols c and g are written last (e.g., Btvg), with one exception. If the symbol f (frozen soil or water) is used together with any of the other symbols in this rule, it is written last, e.g., Cdgf.
  5. If a genetic horizon is buried, the suffix b is written last, e.g., Oab.
  6. Suffix symbols h, s, and w are not used with g, k, kk, n, o, q, y, yy, or z.
  7. If the above rules do not apply to certain suffixes, such as k, kk, q, y, or yy, the suffixes may be listed together in order of assumed dominance or alphabetically if dominance is not a concern.

A B horizon that has a significant accumulation of clay and also shows development of color or structure, or both, is designated “Bt” (suffix symbol t has precedence over symbols w, s, and h). A B horizon that is gleyed or that has accumulations of carbonates, sodium, silica, gypsum, salts more soluble than gypsum, or residual accumulations of sesquioxides carries the appropriate symbol: g, k, kk, n, q, y, yy, z, or o. If illuvial clay is also present, the symbol t precedes the other symbol, e.g., Bto.

Vertical Subdivisions

Commonly, a horizon or layer designated by a single letter or a combination of letters has to be subdivided. For this purpose, numbers are added to the letters of the horizon designation. These numbers follow all the letters. Within a sequence of C horizons, for example, successive layers may be designated C1, C2, C3, etc. If the lower horizons are strongly gleyed and the upper horizons are not strongly gleyed, they may be designated C1-C2-Cg1-Cg2 or C-Cg1-Cg2-R.

These conventions apply regardless of the purpose of the subdivision. In many soils a horizon that could be identified by a single set of letters is subdivided to recognize differences in morphological features, such as structure, color, or texture. These divisions are numbered consecutively, but the numbering starts again at 1 when any letter of the horizon symbol changes, e.g., Bt1-Bt2-Btk1-Btk2 (not Bt1-Bt2-Btk3-Btk4). The numbering of vertical subdivisions within consecutive horizons is not interrupted at a discontinuity (indicated by a numerical prefix) if the same letter combination is used in both materials, e.g., Bs1-BsBsBs4 (not Bs1-BsBsBs2).

During sampling for laboratory analyses, thick soil horizons are sometimes subdivided even though differences in morphology are not evident in the field. These subdivisions are identified by numbers that follow the respective horizon designations. For example, four subdivisions of a Bt horizon sampled by cm increments are designated Bt1, Bt2, Bt3, and Bt4. If the horizon has already been subdivided because of differences in morphological features, the set of numbers that identifies the additional sampling subdivisions follows the first number. For example, three subdivisions of a Bt2 horizon sampled by cm increments are designated Bt21, Bt22, and Bt The descriptions for each of these sampling subdivisions can be the same, and a statement indicating that the horizon has been subdivided only for sampling purposes can be added.

Discontinuities

Numbers are used as prefixes to horizon designations (specifically, A, V, E, B, C, and R) to indicate discontinuities in mineral soils. These prefixes are distinct from the numbers that are used as suffixes denoting vertical subdivisions.

A discontinuity that can be identified by a number prefix is a significant change in particle-size distribution or mineralogy that indicates a difference in the parent material from which the horizons have formed and/or a significant difference in age, unless the difference in age is indicated by the suffix b. Symbols that identify discontinuities are used only when they can contribute substantially to an understanding of the relationships among horizons. The stratification common to soils that formed in alluvium is not designated as a discontinuity, unless particle-size distribution differs markedly from layer to layer (i.e., particle-size classes are strongly contrasting) even though genetic horizons may have formed in the contrasting layers.

If a soil formed entirely in one kind of material, the whole profile is understood to be material 1 and the number prefix is omitted from the symbol. Similarly, the uppermost material in a profile consisting of two or more contrasting materials is understood to be material 1 and the number is omitted. Numbering starts with the second layer of contrasting material, which is designated 2. Underlying contrasting layers are numbered consecutively. Even when the material of a layer below material 2 is similar to material 1, it is designated 3 in the sequence; the numbers indicate a change in materials, not types of material. Where two or more consecutive horizons have formed in the same kind of material, the same prefix number indicating the discontinuity is applied to all the designations of horizons in that material, for example, Ap-E-BtBtBtBC. The suffix numbers designating vertical subdivisions of the Bt horizon continue in consecutive order across the discontinuity. However, vertical subdivisions do not continue across lithologic discontinuities if the horizons are not consecutive or contiguous to each other. If other horizons intervene, another vertical numbering sequence begins for the lower horizons, for example, A-C1-CBwBwCC2.

If an R layer is below a soil that formed in residuum and if it is similar to the material from which the soil developed, the number prefix is not used. The prefix is used, however, if it is thought that the R layer would weather to material unlike that in the solum, e.g., A-Bt-C-2R or A-Bt-2R. If part of the solum has formed in residuum, the symbol R is given the appropriate prefix, for example, Ap-BtBtBtCCR.

A buried genetic horizon (designated by the suffix b) requires special consideration. It is obviously not in the same deposit as the overlying horizons. Some buried horizons, however, formed in material that is lithologically like the overlying deposit. In this case, a prefix is not used to distinguish material of the buried horizon. If the material in which a horizon of a buried soil formed is lithologically unlike the overlying material, the discontinuity is indicated by a number prefix and the symbol for the buried horizon also is used, for example, Ap-Bt1-Bt2-BC-C-2ABb-2BtbBtbC.

Discontinuities between different kinds of layers in organic soils are not identified. In most cases, such differences are identified by letter suffixes if the different layers are organic materials (e.g., Oe vs. Oa) or by the master horizon symbol if the different layers are mineral or limnic materials (e.g., Oa vs. Ldi).

The Prime Symbol

If two or more horizons with identical number prefixes and letter combinations are separated by one or more horizons with a different horizon designation, identical letter and number symbols can be used for those horizons with the same characteristics. For example, the sequence A-E-Bt-E-Btx-C identifies a soil that has two E horizons. To emphasize this characteristic, the prime symbol (´) is added after the symbol of the lower of the two horizons that have identical designations, e.g., A-E-Bt-E´-Btx-C. The prime symbol is placed after the master horizon symbol and before the suffix letter symbol or symbols (if used), for example, B´t.

The prime symbol is not used unless all letter and number prefixes are completely identical. The sequence A-Bt1-BtE-2BtBt2 is an example. Because it has two Bt master horizons of different lithologies, the Bt horizons are not identical and the prime symbol is not needed. The prime symbol is used for soils with lithologic discontinuities if horizons have identical designations. For example, a soil with the sequence A-C-2Bw-2Bc-2B´w-3Bc has two identical 2Bw horizons but two different Bc horizons (2Bc and 3Bc); the prime symbol is used only with the lower 2Bw horizon (2B´w). In the rare cases where three layers have identical letter symbols, double prime symbols can be used for the lowest of these horizons, for example, E´´.

Vertical subdivisions of horizons or layers (number suffixes) are not taken into account when the prime symbol is assigned. The sequence A-E-Bt-E´-B´t1-B´t2-B´t3-C is an example.

These same principles apply in designating layers of organic soils. The prime symbol is used only to distinguish two or more horizons that have identical symbols. For example, Oi-C-O´i-C´ indicates a soil with two identical Oi and C layers and Oi-C-Oe-C´ indicates a soil with two identical C layers. The prime symbol is added to the lower layers to differentiate them from the upper layers.

The Caret Symbol

The caret symbol (^) is used as a prefix to indicate horizons and layers that formed in human-transported material. This material has been moved horizontally onto a pedon from a source area outside of that pedon by purposeful human activity, usually with the aid of machinery or hand tools. Number prefixes may be used before the caret symbol to indicate the presence of discontinuities within the human-transported material (e.g., ^Au-^Bwu-^BCu-2^Cu^Cu2) or between the human-transported material and underlying horizons formed in other parent materials (e.g., ^A-^C^CBwb).

Sample Horizons and Sequences

The following examples illustrate some common horizon and layer sequences of important soils (subgroup taxa) and the use of numbers to identify vertical subdivisions and discontinuities. Transitional horizons, combination horizons, and the use of the prime and caret symbols are also illustrated.

Mineral Soils

Typic Hapludoll: A1-A2-Bw-BC-C
Typic Haplustoll: Ap-A-Bw-Bk-Bky1-Bky2-C
Cumulic Haploxeroll: Ap-A-Ab-C-2C-3C
Typic Argialboll: Ap-A-E-Bt1-Bt2-BC-C
Typic Argiaquoll: A-AB-BA-Btg-BCg-Cg
Alfic Udivitrand: Oi-A-Bw1-BwE/Bt-2Bt/EBt/EBtxBtx2
Entic Haplorthod: Oi-Oa-E-Bs1-Bs2-BC-C
Typic Haplorthod: Ap-E-Bhs-Bs-BC-C1-C2
Typic Fragiudalf: Oi-A-E-BE-Bt1-Bt2-B/E-Btx1-Btx2-C
Typic Haploxeralf: A1-A2-BAt-2BtBtBtBC-2C
Glossic Hapludalf: Ap-E-B/E-Bt1-Bt2-C
Typic Paleudult: A-E-Bt1-Bt2-B/E-B´t1-B´t2-B´t3
Typic Hapludult: Oi-A1-A2-BA-Bt1-Bt2-BC-C
Arenic Plinthic Paleudult: Ap-E-Bt-Btc-Btv1-Btv2-BC-C
Xeric Haplodurid: A-Bw-Bkq-2Bkqm
Vertic Natrigypsid: A-Btn-Btkn-Bky-2By-2BCy-2Cr
Typic Calciargid: A-Bt-Btk1-Btk2-C
Typic Dystrudept: Ap-Bw1-Bw2-C-R
Typic Fragiudept: Ap-Bw-E-Bx1-Bx2-C
Typic Endoaquept: Ap-AB-Bg1-Bg2-BCg-Cg
Typic Haplustert: Ap-A-Bss-BCss-C
Typic Hapludox: Ap-A/B-Bo1-Bo2-Bo3-Bo4-Bo5
Typic Udifluvent: Ap-C-Ab-C´
Glacic Histoturbel: Oi-OA-Bjjg-Wf-Cgf

Organic Soils

Typic Haplosaprist: Oap-Oa1-Oa2-Oa3-C
Typic Sphagnofibrist: Oi1-Oi2-Oi3-Oe
Limnic Haplofibrist: Oi-Lco-O´i1-O´i2-L´co-Oe-C
Lithic Cryofolist: Oi-Oa-R
Typic Hemistel: Oi-Oe-Oef

Human-Altered Soils

Anthrodensic Ustorthent: ^Ap-^C/B-^Cd-2C
Anthroportic Udorthent: ^Ap-^Cu-Ab-Btb-C

Subaqueous Soils

Psammentic Frasiwassents: A1-A2-CA-Cg1-Cg2-Cg3-Cg4
Thapto-Histic Sulfiwassents: Ase-Cse1-Cse2-Oase1-Oa1-Oa2
Sulfic Psammowassents: A-Cg1-Cg2-Aseb-C´g-A´seb-C´´g1-C´´g2-C´´g3

Cyclic and Intermittent Horizons and Layers

Soils with cyclic or intermittent horizons pose special challenges in describing soil profiles. The profile of a soil having cyclic horizons exposes layers whose boundaries are near the surface at one point and extend deep into the soil at another. The aggregate horizon thickness may be only 50 cm at one place but more than cm at a place 2 meters away. The cycle repeats. It commonly has considerable variation in both depth and horizontal interval but still has some degree of regularity. When the soil is visualized in three dimensions instead of two, some cyclic horizons extend downward in inverted cones. The cone of the lower horizon fits around the cone of the horizon above. Other cyclic horizons appear wedge-shaped.

The profile of a soil having an intermittent horizon shows that the horizon extends horizontally for some distance, ends, and reappears again some distance away. For example, the horizons of Turbels, which by definition are subject to cryoturbation, are irregular, intermittent, and distorted. A B horizon interrupted at intervals by upward extensions of bedrock into the A horizon is another example. The distance between places where the horizon is absent is commonly variable but has some degree of regularity. It ranges from less than 1 meter to several meters.

For soils with cyclic or intermittent horizons or layers, a soil profile at one place may be unlike a profile only a few meters away. Standardized horizon nomenclature and pedon description forms are not well suited to soil profiles with such variability. When describing these types of soils, it is important to make notes on the individual horizons to record the nature of the variations. Photographs and diagrams can also be used to convey the information. Descriptions of the order of horizontal variation as well as vertical variation within a pedon include the kind of variation, the spacing of cycles or interruptions, and the amplitude of depth variation of cyclic horizons.

Boundaries of Horizons and Layers

A boundary is a relatively sharp plane-like division or a more gradual transitional layer between two adjoining horizons or layers. Most boundaries are zones of transition rather than sharp lines of division. Boundaries vary in distinctness and topography.

Distinctness

Distinctness refers to the thickness of the zone within which the boundary can be located. The distinctness of a boundary depends partly on the degree of contrast between the adjacent layers and partly on the thickness of the transitional zone between them. Distinctness is defined in terms of thickness of the transitional zone as follows:

Very abrupt less than cm
Abrupt to less than 2 cm
Clear 2 to less than 5 cm
Gradual 5 to less than 15 cm
Diffuse 15 cm or more

Very abrupt boundaries occur at some lithologic discontinuities, such as geogenic deposits or strata (tephras, alluvial strata, etc.). They can also occur at the contacts of root-limiting layers. Examples are duripans; fragipans; petrocalcic, petrogypsic, and placic horizons; continuous ortstein; and densic, lithic, paralithic, and petroferric contacts. See Soil Taxonomy (Soil Survey Staff, ) for more information and definitions.

Abrupt soil boundaries, such as those between the E and Bt horizons of many soils, are easily determined. Some boundaries are not readily seen but can be located by testing the soil above and below the boundary. Diffuse boundaries, such as those in many old soils in tropical areas, are very difficult to locate. They require time-consuming comparisons of small specimens of soil from various parts of the profile to determine the midpoint of the transitional zone. For soils that have nearly uniform properties or that change very gradually as depth increases, horizon boundaries are imposed more or less arbitrarily without clear evidence of differences.

Topography

Topography refers to the irregularities of the surface that divides the horizons (fig. ). Terms for topography describe the shape of the contact between horizons as seen in a vertical cross-section. Even though soil layers are commonly seen in vertical section, they are three-dimensional. Terms describing topography of boundaries are:

Smooth.—The boundary is a plane with few or no irregularities.
Wavy.—The boundary has undulations in which depressions are wider than they are deep.
Irregular.—The boundary has pockets that are deeper than they are wide.
Broken.—One or both of the horizons or layers separated by the boundary are discontinuous and the boundary is interrupted.

Figure Examples of topography classes for horizon boundaries (adapted from Schoeneberger et al., ).

Thickness

The thickness of the horizon or layer is recorded by entering depths for the upper and lower boundaries. For horizons or layers with significant lateral variation in thickness, the average horizon thickness may also be noted.
 

Near Surface Subzones

Background Information

In many soils, the morphology of the uppermost few centimeters (generally from less than 1 to about 18 cm) is strongly controlled by antecedent weather and by soil use. A soil may be freshly tilled and have a loose surface one day and have a strong crust because of a heavy rain the next day. A soil may be highly compacted by livestock and have a firm near surface in one place but have little disturbance to the uppermost few centimeters and be very friable in most other places. These affected soils properties are referred to as “use-dependent” or “dynamic.” See chapter 9 for information about studying dynamic soil properties in the field.

The following discussion provides a set of terms for describing subzones of the near surface and, in particular, the near surface of tilled soils. The horizon designations or symbols for describing these near surface subzones are limited. The suffix d is used for root-restrictive compacted layers; master horizon symbol V may be used to designate some layers with a dominance of vesicular pores. Surface horizons can be subdivided using standard horizon designations to record the subzones. An example horizon sequence could include Ap1 (a mechanically bulked subzone), Ap2 (a water-compacted subzone), and Bd (a mechanically compacted subzone). Descriptions of these separations should also identify the kind of subzone described. Very thin surface crusts (less than about 1 cm thick) are generally described as a special surface feature rather than as a separate layer.

Kinds of Near Surface Subzones

In this section, five kinds of near surface subzones are presented and the general processes leading to their formation are described. The five kinds of subzones are: mechanically bulked, mechanically compacted, water compacted, surficial bulked, and crust (either biological or chemical). Figure shows stylized profiles depicting various combinations of these subzones.

Figure Five kinds of near surface subzones (scale is approximately 18 cm).Identification of subzones is not clear cut. Morphological expression of bulking and compaction may be quite different among soils depending on particle-size distribution, organic matter content, clay mineralogy, water regime, or other factors.

The distinction between a bulked and compacted state for soil material with appreciable shrink-swell potential is partly based on the potential for the transmission of strain on drying over distances greater than the horizontal dimensions of the larger structural units. In a bulked subzone, little or no strain is propagated; in a compacted subzone, the strain is propagated over distances greater than the horizontal dimensions of the larger structural units. Many soils have low shrink-swell potential because of texture, clay mineralogy, or both. For these soils, the expression of cracks cannot be used to distinguish between a bulked state and a compacted state.

The distinction between compaction and bulking is subjective. It is useful to establish a concept of a normal degree of compaction of the near surface and then compare the actual degree of compaction to this. The concept for tilled soils should be the compaction of soil material on level or convex parts of the tillage-determined relief. The soil should have been subject to the bulking action of conventional tillage without the subsequent mechanical compaction. The subzone in question should have been brought to a wet or very moist water state from an appreciably drier condition and then dried to slightly moist or drier at least once. It should not have been subject, however, to a large number of wetting and drying cycles where the maximum wetness involved the presence of free water. If the soil material has a degree of compaction similar to what would be expected, then the term normal compaction is used.

Mechanically Bulked Subzone

The mechanically bulked subzone has undergone, through mechanical manipulation, a reduction in bulk density and an increase in discreteness of structural units, if present. The mechanical manipulation is commonly due to tillage operations. Rupture resistance of the mass overall, inclusive of a number of structural units, is typically loose or very friable and is occasionally friable. Individual structural units may be friable or even firm. Mechanical continuity among structural units is low. Structure grade, if the soil material exhibits structural units less than 20 mm across, is moderate or strong. Strain that results from contraction on drying of individual structural units may not extend across the structural units. Hence, internally initiated desiccation cracks may be weak or absent even though the soil material in a consolidated condition has considerable shrink-swell potential. Cracks may be present, however, if they initiate deeper in the soil. The mechanically bulked subzone is depicted in figure as the first layer in profile a and the second layer in profiles b and c.

Mechanically Compacted Subzone

The mechanically compacted subzone has been subject to compaction, usually due to tillage operations but also by animals. Commonly, mechanical continuity of the fabric and bulk density are increased. Rupture resistance depends on texture and degree of compaction. Generally, friable is the minimum class. Mechanical continuity of the fabric permits propagation of strain (that results on drying) only over several centimeters. Internally initiated cracks appear if the soil material has appreciable shrink-swell potential and drying was sufficient. In some soils this subzone restricts root growth. The suffix d may be used if compaction results in a strong plow pan. The mechanically compacted subzone is the lowest layer of all profiles shown in figure

Water-Compacted Subzone

The water-compacted subzone has been compacted by repetitive large changes in water state without mechanical load, except for the weight of the soil. Repetitive occurrence of free water is particularly conducive to compaction. Depending on texture, moist rupture resistance ranges from very friable through firm. Structural units, if present, are less discrete than those in the same soil material if mechanically bulked. The subzone generally has weak structure or is massive. Mechanical continuity of the fabric is sufficient for strain that originates on drying to propagate appreciable distances. As a consequence, if shrink-swell potential is sufficient, cracks develop on drying. In many soils, the water-compacted subzone replaces the mechanically bulked subzone over time. The replacement can occur in a single year if the subzone is subject to periodic occurrence of free water with intervening periods of being slightly moist or dry. The presence of a water-compacted subzone and the absence of a mechanically bulked subzone is an important consequence of no-till farming systems. The water-compacted subzone is depicted in figure as the second layer of profiles d and e.

Surficial Bulked Subzone

The surficial bulked subzone occurs in the very near surface. Continuity of the fabric is low. Cracks are not initiated in this subzone but may be present (they may initiate in underlying, more compacted soil). The subzone forms by various processes. Frost action under conditions where the soil is drier than wet is one process. Pronounced shrinking and swelling in response to drying and wetting (which is characteristic of Vertisols) is another process. The surficial bulked subzone is depicted in figure as the first layer of profiles c and e.

Crust

A crust is a surficial subzone, typically less than 50 mm thick but ranging to as much as mm thick, that exhibits markedly more mechanical continuity of the soil fabric than the zone immediately beneath. Commonly, the original soil fabric has been reconstituted by water action and the original structure has been replaced by a massive condition. While the material is wet, raindrop impact (including sprinkler irrigation) and freeze-thaw cycles can lead to reconstitution. The crust is depicted in figure as the first layer of profiles b and d.

Crusts may be described in terms of thickness in millimeters, structure and other aspects of the fabric, and consistence, including rupture resistance while dry and micropenetration resistance while wet. Thickness pertains to the zone where reconstitution of the fabric has been pronounced. The distance between surface-initiated cracks (described later in this chapter) may be a useful observation for seedling emergence considerations. If the distance is short, the weight of the crust slabs is low.

Soil material with little apparent reconstitution commonly adheres beneath the crust and is removed with the crust. This soil material, which shows little or no reconstitution, is not part of the crust and does not contribute to the thickness.

Recognized types of soil crusts include biological, chemical and structural.

Biological crusts, which consist of algae, lichens, or mosses, occur on the surface of some soils, especially in some relatively undisturbed settings, such as rangelands. These crusts are easily diminished or destroyed by disturbance.

Chemical crusts commonly occur in arid environments where salty evaporites accumulate at the surface. They include crusts consisting of mineral grains cemented by salts.

Structural crusts form from local transport and deposition of soil material, commonly in tilled fields. They have weaker mechanical continuity than other crusts. The rupture resistance is lower, and the reduction in infiltration may be less than that of crusts with similar texture. Raindrop impact and freeze-thaw cycles contribute to the formation of structural crusts.
 

Root-Restricting Depth

The root-restricting depth is the depth at which physical (including soil temperature) and/or chemical characteristics strongly inhibit root penetration. Restriction means the incapability to support more than a few fine or very fine roots if the depth from the soil surface and the water state (other than the occurrence of frozen water) are not limiting. For cotton, soybeans, and other crops that have less abundant roots than grasses have, the very few class is used instead of the few class. The restriction may be below where plant roots normally occur because of limitations in water state, temperatures, or depth from the surface. The root-restricting depth should be evaluated for the specific plants important to the use of the soil. These plants are indicated in the soil description. The root-restriction depth may differ depending on the plant.

Morphology and Root Restriction

Root-depth observations should be used to make the generalization of root-restricting depth. If these are not available (commonly because roots do not extend to the depth of concern) then inferences may be made from morphology. A change in particle-size distribution alone (e.g., loamy sand over gravel) is not typically a basis for physical root restriction. Some guidelines for inferring physical restriction are given below. Chemical restrictions, such as high levels of extractable aluminum and/or low levels of extractable calcium, are not considered; these are generally not determinable by field examination alone.

Physical root restriction is assumed:

  1. At the contact with bedrock and other continuously cemented materials, regardless of the rupture resistance class or thickness;
  2. For certain horizons or layers, such as fragipans or those consisting of densic materials, that, although non-cemented, are root restrictive by definition; and
  3. For layers with a combination of structure, consistence, and/or penetration resistance that suggests that the resistance of the soil fabric to root entry is high and that vertical cracks and planes of weakness for root entry are absent or widely spaced (i.e., more than 10 cm apart) as follows:
    1. For a zone more than 10 cm thick that when very moist or wet is very firm (firm, if sandy) or firmer or that has a penetration resistance class of large (i.e., high or higher), and is massive or platy or has weak structure of any type.
    2. For a zone that has structural units of any grade with a vertical repeat distance of more than 10 cm and while very moist or wet is very firm (firm, if sandy) or extremely firm, or has a large (i.e., high or higher) penetration resistance.

Classes of Root-Restricting Depth

Terms describing depth to physical restriction for roots are:

Very shallow less than 25 cm
Shallow 25 to less than 50 cm
Moderately deep 50 to less than cm
Deep to less than cm
Very deep cm or more
 

Particle-Size Distribution

This section discusses particle-size distribution of mineral soil separates. Fine earth indicates particles smaller than 2 mm in diameter. Fragments 2 mm or larger consist of rock fragments, pieces of geologic or pedogenic material with a strongly cemented or more cemented rupture-resistance class; pararock fragments, pieces of geologic or pedogenic material with an extremely weakly cemented to moderately cemented rupture-resistance class; and discrete artifacts, pieces of human-manufactured material. Particle-size distribution of fine earth is determined in the field mainly by feel. The content of rock fragments, pararock fragments, and discrete artifacts is an estimate of the proportion of the soil volume that they occupy.

Soil Separates

After pretreatment to remove organic matter, carbonates, soluble salts, and other cementing agents and after dispersion to physically separate individual soil particles, the U.S. Department of Agriculture uses the following size separates for fine-earth fraction:

Very coarse sand < to > mm
Coarse sand to > mm
Medium sand to > mm
Fine sand to > mm
Very fine sand to > mm
Coarse silt to > mm
Fine silt to > mm
Coarse clay to > mm
Fine clay less than or equal to mm

Figure compares the USDA system for naming various sizes of soil separates with four other systems: International (Soil Survey Staff, ); Unified (ASTM, ); AASHTO (AASHTO, a, b); and Modified Wentworth (Ingram, ).

Figure Relationships among particle-size classes of the USDA system and four other systems.

Soil Texture

Soil texture refers to the weight proportion of the separates for particles less than 2 mm in diameter as determined from a laboratory particle-size distribution. The pipette method is the preferred standard, but the hydrometer method also is used in field labs (Soil Survey Staff, ). If used, the hydrometer method should be noted with the results.

Field estimates of soil texture class are based on qualitative criteria, such as how the soil feels (gritty, smooth, sticky) and how it responds to rubbing between the fingers to form a ribbon. Estimated field texture class should be checked against laboratory determinations, and the field criteria used to estimate texture class should be adjusted as necessary to reflect local conditions. Sand particles feel gritty and can be seen individually with the naked eye. Silt particles have a smooth feel to the fingers when dry or wet and cannot be seen individually without magnification. Clay soils are sticky in some areas and not sticky in others. For example, soils dominated by smectitic clays feel different from soils that contain similar amounts of micaceous or kaolinitic clay. The relationships that are useful for judging texture of one kind of soil may not apply as well to another kind.

Some soils are not dispersed completely in the standard laboratory particle-size analysis. Examples include soils with andic soil properties (high amounts of poorly crystalline, amorphous minerals) and soils with high contents of gypsum (more than about 25 percent). For soils like these, for which the estimated field texture class and the laboratory measured particle-size distribution differ markedly, the field texture is referred to as apparent because it is not an estimate that correlates well with the results of a laboratory test. Apparent field texture is only a tactile evaluation and does not infer laboratory test results. The twelve texture classes (fig. ) are sands, loamy sands, sandy loams, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, and clay. Subclasses of sand are coarse sand, sand, fine sand, and very fine sand. Subclasses of loamy sands and sandy loams that are based on sand size are named similarly.

Definitions of Soil Texture Classes and Subclasses

Sands.—Material has more than 85 percent sand, and the percentage of silt plus times the percentage of clay is less than

Coarse sand.—Material has a total of 25 percent or more very coarse and coarse sand and less than 50 percent any other single grade of sand.

Sand.—Material has a total of 25 percent or more very coarse, coarse, and medium sand, a total of less than 25 percent very coarse and coarse sand, and less than 50 percent fine sand and less than 50 percent very fine sand; OR material has 25 percent or more very coarse and coarse sand and 50 percent or more medium sand.

Fine sand.—Material has 50 percent or more fine sand, and fine sand exceeds very fine sand; OR material has a total of less than 25 percent very coarse, coarse, and medium sand and less than 50 percent very fine sand.

Very fine sand.—Material has 50 percent or more very fine sand.

Loamy sands.—Material has between 70 and 90 percent sand, the percentage of silt plus times the percentage of clay is 15 or more, and the percentage of silt plus twice the percentage of clay is less than

Loamy coarse sand.—Material has a total of 25 percent or more very coarse and coarse sand and less than 50 percent any other single grade of sand.

Loamy sand.—Material has a total of 25 percent or more very coarse, coarse, and medium sand, a total of less than 25 percent very coarse and coarse sand, and less than 50 percent fine sand and less than 50 percent very fine sand; OR material has a total of 25 percent or more very coarse and coarse sand and 50 percent or more medium sand.

Loamy fine sand.—Material has 50 percent or more fine sand or less than 50 percent very fine sand and a total of less than 25 percent very coarse, coarse, and medium sand.

Loamy very fine sand.—Material has 50 percent or more very fine sand.

Sandy loams.—Material has 7 to less than 20 percent clay and more than 52 percent sand, and the percentage of silt plus twice the percentage of clay is 30 or more; OR material has less than 7 percent clay and less than 50 percent silt, and the percentage of silt plus twice the percentage of clay is 30 or more.

Coarse sandy loam.—Material has a total of 25 percent or more very coarse and coarse sand and less than 50 percent any other single grade of sand; OR material has a total of 30 percent or more very coarse, coarse, and medium sand, and very fine sand is 30 to less than 50 percent.

Sandy loam.—Material has a total of 30 percent or more very coarse, coarse, and medium sand but a total of less than 25 percent very coarse and coarse sand, less than 30 percent fine sand, and less than 30 percent very fine sand; OR material has a total of 15 percent or less very coarse, coarse, and medium sand, less than 30 percent fine sand, and less than 30 percent very fine sand with a total of 40 percent or less fine and very fine sand; OR material has a total of 25 percent or more very coarse and coarse sand and 50 percent or more medium sand.

Fine sandy loam.—Material has 30 percent or more fine sand, less than 30 percent very fine sand, and a total of less than 25 percent very coarse and coarse sand; OR material has a total of 15 to less than 30 percent very coarse, coarse, and medium sand and a total of less than 25 percent very coarse and coarse sand; OR material has a total of 40 percent or more fine and very fine sand (and fine sand equals or exceeds very fine sand) and a total of 15 percent or less very coarse, coarse, and medium sand; OR material has a total of 25 percent or more very coarse and coarse sand and 50 percent or more fine sand.

Very fine sandy loam.—Material has 30 percent or more very fine sand and a total of less than 15 percent very coarse, coarse, and medium sand, and very fine sand exceeds fine sand; OR material has 40 percent or more fine and very fine sand (and very fine sand exceeds fine sand) and a total of less than 15 percent very coarse, coarse, and medium sand; OR material has 50 percent or more very fine sand and a total of 25 percent or more very coarse and coarse sand; OR material has a total of 30 percent or more very coarse, coarse, and medium sand and 50 percent or more very fine sand.

Loam.—Material has 7 to less than 27 percent clay, 28 to less than 50 percent silt, and 52 percent or less sand.

Silt loam.—Material has 50 percent or more silt and 12 to less than 27 percent clay; OR material has 50 to less than 80 percent silt and less than 12 percent clay.

Silt.—Material has 80 percent or more silt and less than 12 percent clay.

Sandy clay loam.—Material has 20 to less than 35 percent clay, less than 28 percent silt, and more than 45 percent sand.

Clay loam.—Material has 27 to less than 40 percent clay and more than 20 to 45 percent sand.

Silty clay loam.—Material has 27 to less than 40 percent clay and 20 percent or less sand.

Sandy clay.—Material has 35 percent or more clay and more than 45 percent sand.

Silty clay.—Material has 40 percent or more clay and 40 percent or more silt.

Clay.—Material has 40 percent or more clay, 45 percent or less sand, and less than 40 percent silt.

The USDA textural triangle is shown in figure A soil sample is assigned to one of the twelve soil texture classes according to the values for the proportions of sand, silt, and clay, which are located along each of the three axes. The eight subclasses in the sand and loamy sand groups provide refinement that in some cases may be greater than can be consistently determined by field techniques. Only those distinctions that are significant to use and management and that can be consistently made in the field should be applied when determinations of texture are based on field estimates alone.

Figure USDA textural triangle showing the percentages of clay, silt, and sand in the 12 basic texture classes.

Groupings of Soil Texture Classes

The need for fine distinctions in the texture of the soil layers results in a large number of classes and subclasses of soil texture. It commonly is convenient to speak generally of broad groups or classes of texture. Table provides an outline of three general soil texture groups and five subgroups. In some areas where soils have a high content of silt, a fourth general class, silty soil materials, may be used for silt and silt loam.

General texture groups and subgroups*Texture classes
Sandy soil materials
Coarse texturedSands (coarse sand, sand, fine sand, very fine sand); loamy sands (loamy coarse sand, loamy sand, loamy fine sand, loamy very fine sand)
Loamy soil materials
Moderately coarse texturedCoarse sandy loam, sandy loam, fine sandy loam
Medium texturedVery fine sandy loam, loam, silt loam, silt
Moderately fine texturedClay loam, sandy clay loam, silty clay loam
Clayey soil materials
Fine texturedSandy clay, silty clay, clay

* Note: These are not the sandy, loamy, and clayey family particle-size classes defined in Soil Taxonomy.

Terms Used in Lieu of Soil Texture

There are some horizons or layers for which soil texture class terms are not applicable. These include bedrock and other cemented horizons (such as petrocalcic horizons, duripans, etc.), those composed of organic soil materials, and those composed of water, either liquid or frozen, below a mineral or organic soil surface layer. Other exceptions include layers composed of more than 90 percent rock fragments or artifacts and horizons or layers composed of 40 percent or more gypsum in the fine-earth fraction (and that are not cemented). These exceptions are discussed below.

Soil Materials with a High Content of Gypsum

For soil materials with 40 percent or more, by weight, gypsum in the fine-earth fraction, gypsum dominates the physical and chemical properties of the soil to the extent that particle-size classes are not meaningful. Two terms in lieu of texture are used:

Coarse gypsum material.—50 percent or more of the fine-earth fraction is comprised of particles ranging from to mm in diameter.

Fine gypsum material.—Less than 50 percent of the fine-earth fraction is comprised of particles ranging from to mm in diameter.

Bedrock and Cemented Horizons

These horizons or layers are described as bedrock or cemented material. Additional information about the kind of rock, degree of cementation, and kind of cementing agent can also be provided.

Water Layers

These layers are described as water or ice. They only refer to subsurface layers, such as in a floating bog. Figure shows a subsoil layer of ice.

Soil Materials with a High Content of Rock or Pararock Fragments

For soil materials with more than 90 percent rock or pararock fragments, there is not enough fine earth to determine the texture class. In these cases, the terms gravel, cobbles, stones, boulders, channers, and flagstones or their pararock fragment equivalents are used. Size range and shape for these terms are described under “Rock Fragments and Pararock Fragments” and are summarized in table

Soil Materials with a High Content of Artifacts

For soil materials with more than 90 percent artifacts, the term artifacts is used.

Organic Soils

Layers that are not saturated with water for more than a few days at a time are organic if they have 20 percent or more organic carbon. Layers that are saturated for longer periods, or were saturated before being drained, are organic if they have 12 percent or more organic carbon and no clay, 18 percent or more organic carbon, and 60 percent or more clay or have a proportional amount of organic carbon, between 12 and 18 percent, if the clay content is between 0 and 60 percent. The required organic carbon content for saturated soils having between 0 and 60 percent clay can be calculated as: OCrequired = 12 + ( * percent clay). Soils with more than 60 percent clay need an organic carbon content of at least 18 percent.

The kind and amount of the mineral fraction, the kind of organisms from which the organic material was derived, and the state of decomposition affect the properties of the soil material. Descriptions include the percentage of undecomposed fibers and the solubility in sodium pyrophosphate of the humified material. Attention should be given to identifying and estimating the volume occupied by sphagnum fibers, which have extraordinary high water retention. When squeezed firmly in the hand to remove as much water as possible, sphagnum fibers are lighter in color than fibers of hypnum and most other mosses.

Fragments of wood more than 20 mm across and so undecomposed that they cannot be crushed by the fingers when moist or wet are called wood fragments. They are comparable to rock fragments in mineral soils and are described in a comparable manner.

Saturated organic soil materials.—The types of organic soil materials that are described in saturated organic soil materials are:

Muck.—Well decomposed organic soil material with a low content of fibers (plant tissue excluding live roots).

Peat.—Slightly decomposed organic soil material with a high content of original fibers.

Mucky peat.—Organic soil material that is intermediate in degree of decomposition, fiber content, bulk density, and water content between muck and peat.

Muck, peat, and mucky peat may be described in both organic and mineral soils provided the soils are saturated with water for 30 or more cumulative days in normal years or are artificially drained. These materials only qualify for the diagnostic sapric, fibric, and hemic soil material of Soil Taxonomy when they occur in organic soils (i.e., the soil of the order Histosols and the suborder Histels).

Non-saturated organic soil materials.—The types of organic soil materials that are described in layers not saturated for 30 or more cumulative days are:

Highly decomposed plant material.—Well decomposed, organic soil material with a low content of fibers (plant tissue excluding live roots).

Moderately decomposed plant material.—Material intermediate in degree of decomposition, fiber content, bulk density, and water content between highly decomposed and slightly decomposed plant material.

Slightly decomposed plant material.—Slightly decomposed organic soil material with a high content of original fibers.

Modifiers for Terms Used in Lieu of Texture

Modifiers may be needed to better describe the soil material making up the horizon or layer. These include terms for significant amounts of particles mm or larger (rock fragments, pararock fragments, or artifacts) and terms that indicate the composition of the soil material.

Soil Materials with Rock Fragments, Pararock Fragments, or Artifacts

To describe soils with 15 percent or more, by volume, rock fragments, pararock fragments, or artifacts, the texture terms are modified with terms indicating the amount and kind of fragments. Examples include very gravelly loam, extremely paracobbly sand, and very artifactual sand. The conventions for use of these terms and the definitions of class terms are discussed in the following sections on rock fragments, pararock fragments, and artifacts.

Class Modifiers Indicating Soil Material Composition

Soil composition modifiers are used for some soils that have andic properties or formed in volcanic materials, soils that have a high content of gypsum, some organic soil materials, and mineral soil materials with a high content of organic matter. Terms are also provided for limnic soil materials and permanently frozen layers (permafrost).

Soil Materials with Andic Properties or Volcanic Origin

Hydrous.—Material that has andic soil properties and an undried 15 bar ( kPa) water content of percent or more of the dry weight (e.g., hydrous clay).

Medial.—Material that has andic soil properties and has a 15 bar ( kPa) water content of less than percent on undried samples and of 12 percent or more on air-dried samples (e.g., medial silt loam).

Ashy.—Material that has andic soil properties and is neither hydrous nor medial, or material that does not have andic soil properties and the chemistry and physical makeup of its fine-earth fraction reflects the weathering processes of volcanic materials (e.g., ashy loam). The weathering processes of volcanic materials are evidenced by 30 percent or more particles to mm in diameter, of which 5 percent or more is composed of volcanic glass and the [(aluminum plus ½ iron percent by ammonium oxalate) times 60] plus the volcanic glass percent is equal to or more than

Soil Materials with Gypsum

Gypsiferous.—Material that contains 15 to less than 40 percent, by weight, gypsum (e.g., gypsiferous fine sandy loam).

For material that has 40 percent or more gypsum, a term in lieu of texture is used (e.g., fine gypsum material or coarse gypsum material, defined above).

Organic Soil Materials

Modifiers are only used with the “in lieu of texture” terms muck, peat, or mucky peat. The following modifiers are used only for organic soil materials that are saturated with water for 30 or more cumulative days in normal years or are artificially drained.

Woody.—Material contains 15 percent or more wood fragments larger than 20 mm in size or contains 15 percent or more fibers that can be identified as wood origin and has more wood fibers than any other kind of fiber (e.g., woody muck).

Grassy.—Material contains more than 15 percent fibers that can be identified as grass, sedges, cattails, and other grasslike plants and contains more grassy fibers than any other kind of fiber (e.g., grassy mucky peat).

Mossy.—Material contains more than 15 percent fibers that can be identified as moss and contains more moss fibers than any other kind of fiber (e.g., mossy peat).

Herbaceous.—Material contains more than 15 percent fibers that can be identified as herbaceous plants other than moss and grass or grasslike plants and has more of these fibers than any other kind of fiber (e.g., herbaceous muck).

Mineral Soil Materials with a High Content of Organic Matter

Highly organic.—Term indicates near surface horizons of mineral soils that are saturated with water for less than 30 cumulative days in normal years and are not artificially drained (e.g., highly organic loam). Excluding live roots, the horizon has organic carbon content (by weight) of one of the following:

•  5 to < 20 percent if the mineral fraction contains no clay,
•  12 to < 20 percent if the mineral fraction contains 60 percent or more clay, or
•  [5 + (clay percentage multiplied by )] to < 20 percent if the mineral fraction contains less than 60 percent clay.

Mucky.—Term indicates near surface horizons of mineral soils that are saturated with water for 30 or more cumulative days in normal years or are artificially drained (e.g., mucky silt loam). Excluding live roots, the horizon has more than 10 percent organic matter and less than 17 percent fibers.

Peaty.—Term indicates near surface horizons of mineral soils that are saturated with water for 30 or more cumulative days in normal years or are artificially drained (e.g., peaty clay loam). Excluding live roots, the horizon has more than 10 percent organic matter and 17 percent or more fibers.

Limnic Soil Materials

Limnic soil materials occur in layers underlying some soils of the soil order Histosols. By definition (see Soil Taxonomy) they are not recognized in mineral soils. They are mineral or organic soil materials originating from aquatic organisms or from aquatic plants that were later altered by aquatic organisms. The following terms are used to describe the origin of the limnic materials:

Coprogenous.—Material contains many very small ( to mm) fecal pellets (e.g., coprogenous sandy loam).

Diatomaceous.—Material is composed dominantly of diatoms (e.g., diatomaceous silt loam).

Marly.—Material is composed dominantly of calcium carbonate “mud” (e.g., marly silty clay).

Layers for which these terms are used may or may not also meet the definition for coprogenous earth, diatomaceous earth, or marl as defined in Soil Taxonomy.

Permafrost

Layers of permafrost are described as permanently frozen (e.g., permanently frozen loamy sand).
 

Rock Fragments and Pararock Fragments

Rock fragments are unattached pieces of geologic or pedogenic material 2 mm in diameter or larger that have a strongly cemented or more cemented rupture-resistance class. Pararock fragments are unattached pieces of geologic or pedogenic material 2 mm in diameter or larger that are extremely weakly cemented through moderately cemented. Pararock fragments are not retained on sieves because they are crushed by grinding during the preparation of samples for particle-size analysis in the laboratory. Rock fragments and pararock fragments include all sizes between mm and horizontal dimensions smaller than the size of a pedon. The words “rock” and “pararock” are used here in the broad sense and connote more than just natural fragments of geologic material. Thus, rock and pararock fragments may be discrete, cemented pieces of bedrock, bedrock-like material, durinodes, concretions, nodules, or pedogenic horizons (e.g., petrocalcic fragments). Artifacts, however, are not included as rock or pararock fragments. They are described separately.

Rock fragments and pararock fragments are described by size, shape, hardness, roundness, and kind of fragment. The classes are gravel, cobbles, channers, flagstones, stones, and boulders and their pararock counterparts (i.e., paragravel, paracobbles, etc.) (table ). If a size or range of sizes predominates, the class is modified (e.g., “fine gravel,” “cobbles to mm in diameter,” “channers 25 to 50 mm in length”).

Shape and sizeNoun*Adjective*
Nonflat fragments (spherical or cubelike):
2–76 mm diameterGravelGravelly
    2–5 mm diameter     Fine gravel     Fine gravelly
     > 5–20 mm diameter     Medium gravel     Medium gravelly
     > 20–76 mm diameter     Coarse gravel     Coarse gravelly
> 76– mm diameterCobblesCobbly
> – mm diameterStonesStony
> mm diameterBouldersBouldery
Flat fragments:
2– mm longChannersChannery
> – mm longFlagstonesFlaggy
> – mm longStonesStony
> mm longBouldersBouldery

* For fragments that are less than strongly cemented, the prefix “para” is added to the terms in this table to form either a descriptive noun or the adjective for the texture modifier (e.g., paracobbles, paragravelly).

Gravel and paragravel are a collection of fragments that have diameters ranging from 2 to 76 mm. Individual fragments in this size range are properly referred to as “pebbles,” not “gravels.” The term gravel as used here indicates the collection of pebbles in a soil horizon and does not imply a geological formation. The terms “pebble” and “cobble” are typically restricted to rounded or subrounded fragments; however, they can be used to describe angular fragments that are not flat. Words such as “chert,” “limestone,” and “shale” refer to a kind or lithology of rock, not a piece of rock. The composition of the fragments can be given, for example: “chert gravel,” “limestone channers,” “siltstone parachanners.”

The upper size limit of gravel and paragravel is 76 mm (3 inches). This coincides with the upper limit used by many engineers for grain-size distribution computations. The 5-mm and mm divisions for the separation of fine, medium, and coarse gravel coincide with the sizes of openings in the number 4 screen (mm) and the ¾-inch (mm) screen used in engineering.

The mm (3-inch) limit separates gravel from cobbles, the mm (inch) limit separates cobbles from stones, and the mm (inch) limit separates stones from boulders. The mm (6-inch) and mm (inch) limits for thin, flat channers and flagstones, respectively, follow conventions used for many years to provide class limits for plate-shaped and crudely spherical rock fragments that have about the same soil use implications as the mm limit for spherical shapes.

Estimating Rock Fragments in the Soil

Rock fragments in the soil can greatly influence use and management. It is important to not only consider the total amount of rock fragments, but also the proportions of the various size classes (gravel, cobbles, stones, etc.). A soil with 10 percent stones is quite different from one with 10 percent gravel. When developing interpretive criteria, a distinction must be made between volume and weight percent of rock fragments. Field descriptions generally record estimates of volume, while laboratory measurements of rock fragments are given as weight for the various size classes.

The National Cooperative Soil Survey in the United States uses interpretive algorithms based on weight percent of the > , > , > , and mm fractions when rating soils for various potential uses. The first two size ranges are on a whole soil basis, and the latter two are on a < 76 mm basis. For the > and > mm fractions, weighing is generally impracticable and volume percentage estimates are made from areal percentage measurements by point-count or line-intersect methods. Length of the transect or area of the exposure should be at least 50 times, and preferably times, the area or dimensions of the rock fragment size that encompasses about 90 percent of the rock fragment volume. For the < 76 mm weight, measurements are feasible but may require 50 to 60 kg of sample if appreciable rock fragments near 76 mm are present. An alternative is to obtain volume estimates for the mm fraction and weight estimates for the < 20 mm fraction. This method is preferred because of the difficulty in visual evaluation of the 2 to 5 mm size separations. The weight percentages of > mm and mm fractions may be converted to volume estimates and placed on a < 76 mm base by computation.

Terms for Rock Fragments and Their Use in Modifying Texture Classes

The adjectival form of a class name of rock fragments or pararock fragments (table ) is used as a modifier of the texture class name, e.g., paragravelly loam, very cobbly sandy loam. Table provides rules for determining the proper texture modifier term for material with a mixture of rock fragment sizes. This section also provides rules for assigning terms for soils with a mixture of rock and pararock fragments.

The following classes, based on volume percentages, are used:

Less than 15 percent.—No texture modifier terms are used with soils having less than 15 percent gravel, paragravel, cobbles, paracobbles, channers, parachanners, flagstones, or paraflagstones.

15 to less than 35 percent.—The adjectival term of the dominant kind of fragment is used as a modifier of the texture class, e.g., gravelly loam, parachannery silt loam, cobbly sandy loam.

35 to less than 60 percent.—The adjectival term of the dominant kind of rock fragment is used with the word “very” as a modifier of the texture class, e.g., very gravelly loam, very parachannery silt loam, very cobbly loamy sand (fig. ).

60 to less than 90 percent.—The adjectival term of the dominant kind of rock fragment is used with the word “extremely” as a modifier of the texture class, e.g., extremely gravelly loam, extremely parachannery silt loam, extremely cobbly sandy loam.

90 percent or more.—No texture modifier terms are used. If there is too little fine earth to determine the texture class (less than about 10 percent, by volume) a term in lieu of texture (i.e., gravel, cobbles, stones, boulders, channers, flagstones, or their pararock fragment equivalents) is used as appropriate.

Total rock fragments
(Vol. %)
Gravel (GR), cobbles (CB), stones (ST), and boulders (BY)
(Substitute channers for gravel and flagstones for cobbles, where applicable)
If GR ≥
CB +
2 ST +
BY
If CB ≥
ST +
2 BY
If ST ≥
BY
If ST <
BY
≥ 15 < 35GravellyCobblyStonyBouldery
≥ 35 < 60Very gravellyVery cobblyVery stonyVery bouldery
≥ 60 < 90Extremely gravellyExtremely cobblyExtremely stoneExtremely bouldery
≥ 90GravelCobblesStonesBoulders

Figure A soil in which the layers below a depth of about 20 cm are very cobbly loamy sand. Left side of scale is in cm increments.The class limits apply to the volume of the layer occupied by all rock fragments 2 mm in diameter or larger. The soil generally contains fragments smaller or larger than those identified by the term. For example, very cobbly sandy loam typically contains gravel but “gravelly” is not in the name. The use of a term for larger pieces of rock, such as boulders, does not imply that the pieces are entirely within a given soil layer. A single boulder may extend through several layers.

Table can be used to determine the proper modifier if there is a mixture of rock fragment sizes. To use the table, first choose the row with the appropriate total rock fragments. Then read the criteria in the columns under “Gravel, cobbles, stones, and boulders,” starting from the left-most column and proceeding to the right. Stop in the first column in which a criterion is met.

More precise estimates of the amounts of rock fragments than are provided by the defined classes are needed for some purposes. For more precise information, estimates of percentages of each size class or a combination of size classes are included in the description, e.g., “very cobbly sandy loam,” “30 percent cobbles and 15 percent gravel or silt loam,” “about 10 percent gravel.” If loose pieces of rock are significant to the use and management of a soil, they are the basis of phase distinctions among map units. Exposed bedrock is not soil and is identified separately in mapping as a kind of miscellaneous area (i.e., Rock outcrop).

The volume occupied by individual pieces of rock can be seen, and their aggregate volume percentage can be calculated. For some purposes, volume percentage must be converted to weight percentage.

The following rules are used to select texture modifiers if a horizon includes both rock and pararock fragments:

  1. Describe the individual kinds and amounts of rock and pararock fragments.
  2. Do not use a fragment texture modifier if the combined volume of rock and pararock fragments is less than 15 percent.
  3. If the combined volume of rock and pararock fragments is more than 15 percent and the volume of rock fragments is less than 15 percent, assign pararock fragment modifiers based on the combined volume of fragments. For example, use “paragravelly” as a texture modifier for soils with 10 percent rock and 10 percent pararock gravel-sized fragments.
  4. If the volume of rock fragments is 15 percent or more, use the appropriate texture modifier for rock fragments regardless of the volume of pararock fragments.

Rock Fragment Hardness, Roundness, and Kind

Fragment hardness is equivalent to the rupture resistance class for a cemented fragment of specified size that has been air dried and then submerged in water. The hardness of a fragment is significant where the rupture resistance class is strongly cemented or greater. See the section on rupture resistance later in this chapter for details describing the fragment hardness classes and their test descriptions.

Fragment roundness is an expression of the sharpness of the edges and corners of rock fragments and pararock fragments. The roundness of fragments impacts water infiltration, root penetration, and macropore space. The following roundness classes are used:

Very angular Strongly developed faces and very sharp, broken edges
Angular Strongly developed faces and sharp edges
Subangular Detectable flat faces and slightly rounded corners
Subrounded Detectable flat faces and well rounded corners
Rounded Flat faces absent or nearly absent and all corners rounded
Well rounded Flat faces absent and all corners rounded

Fragment kind is the lithology or composition of the 2 mm or larger fraction of the soil. Kinds of fragments are varied based on whether their origin is from a geologic source or a pedogenic source. Examples of kinds of fragments are basalt fragments, durinodes, iron-manganese concretions, limestone fragments, petrocalcic fragments, tuff fragments, and wood fragments.
 

Artifacts

Artifacts are discrete water-stable objects or materials created, modified, or transported from their source by humans, usually for a practical purpose in habitation, manufacturing, excavation, agriculture, or construction activities. Examples are processed wood products, coal combustion by-products, bitumen (asphalt), fibers and fabrics, bricks, cinder blocks, concrete, plastic, glass, rubber, paper, cardboard, iron and steel, altered metals and minerals, sanitary and medical waste, garbage, and landfill waste. Artifacts also include natural materials which were mechanically abraded by human activities (as evidenced by scrapes, gouges, tool marks, etc.), such as shaped or carved stone work, grindstones, and shaped stones and debitage (e.g., stone tool flakes).

Artifacts are generally categorized as either particulate or discrete. The distinction is based on size: particulate artifacts have a diameter of less than 2 mm and discrete artifacts have a diameter of 2 mm or more. Discrete artifacts are easier to identify and are essentially fragments of human origin. Particulate artifacts are sometimes difficult to discern from naturally occurring fine-earth soil material.

Describing Artifacts in Soil

Artifacts are described if they are judged to be durable enough to persist in the soil (resist weathering and leaching) for a few decades or more. Descriptions of artifacts generally include quantity, cohesion, persistence, size, and safety classes. They may also include shape, kind, penetrability by roots, and roundness. Additional attributes (such as those discussed below under the heading “Consistence”) may be described to help understand and interpret the soil. The conventions for describing artifacts are explained in the following paragraphs.

Quantity refers to the estimated volume percent of a horizon or other specified unit occupied by discrete artifacts. If classes (rather than quantitative estimates) are given, they are the same as those described in this chapter for mottles.

Cohesion refers to the relative ability of the artifact to remain intact after significant disturbance. The cohesion classes are:

Cohesive.—Artifacts adhere together sufficiently so that they cannot be easily broken into pieces < 2 mm either by hand or with a simple crushing device, such as a mortar and pestle.

Noncohesive.—Artifacts are easily broken into pieces < 2 mm either by hand or with a simple crushing device, such as a mortar and pestle. Noncohesive artifacts are similar to pararock fragments and will be incorporated into the fine-earth fraction of the soil during routine laboratory sample preparation.

Penetrability describes the relative ease with which roots can penetrate the artifact and potentially extract any stored moisture, nutrients, or toxic elements. The penetrability classes are:

Nonpenetrable.—Roots cannot penetrate through the solid parts of the artifact or between the component parts of the artifact.

Penetrable.—Roots can penetrate through the solid parts of the artifact or between the component parts of the artifact.

Persistence describes the relative ability of solid artifacts to with-stand weathering and decay over time. Local conditions, such as temperature and moisture, significantly impact the persistence of artifacts in the soil. The persistence classes are:

Nonpersistent.—The artifact is susceptible to relatively rapid weathering or decay and is expected to be lost from the soil in less than a decade. Loss of soil mass and eventually subsidence result.

Persistent.—The artifact is expected to remain intact in the soil for a decade or more.

Roundness indicates the sharpness of edges and corners of natural objects, such as rock fragments, and human-manufactured objects, such as artifacts. The artifact roundness classes are the same as those used for fragment roundness (above).

Safety describes the degree of risk to humans from contact with soils that contain artifacts. Physical contact with soils containing dangerous or harmful artifacts should be avoided unless proper training is provided and protective clothing is available. The safety classes are:

Innocuous.—The artifacts are considered to be harmless to living beings. Examples include untreated wood products, iron, bricks, cinder blocks, concrete, plastic, glass, rubber, organic fibers, inorganic fibers, unprinted paper and cardboard, and some mineral and metal products. Sharp innocuous artifacts can cause injury, but the materials themselves are still considered innocuous.

Noxious.—The artifacts are potentially harmful or destructive to living beings unless dealt with carefully. The harm may be immediate or long-term and through direct or indirect contact. Examples include arsenic-treated wood products, batteries, waste and garbage, radioactive fallout, liquid petroleum products, asphalt, coal ash, paper printed with metallic ink, and some mineral and metal products.

Shape is variable among kinds of artifacts. The shape classes are:

Elongated.—One dimension is at least three times longer than both of the others.

Equidimensional.—Dimensions in length, width, and height are approximately similar.

Flat.—One dimension is less than one third that of both of the others, and one dimension is less than three times that of the intermediate dimension.

Irregular.—The form is branching and convoluted.

Size may be measured and reported directly or given as a class. The dimension to which size-class limits apply depends on the shape of the artifact described. If the shape is nearly uniform, size is measured in the shortest dimension, such as the effective diameter of a cylinder or the thickness of a plate. For elongated or irregular bodies, size generally refers to the longest dimension but direct measurements for 2 or 3 dimensions can be given for clarification. The size classes for discrete artifacts are:

Fine 2 to < 20 mm
Medium 20 to < 75 mm
Coarse 75 to < mm
Very coarse ≥ mm

Kinds of Artifacts

There are too many varieties of artifacts to provide a comprehensive list. The most common types include:

  • Noxious and innocuous artifacts
  • Treated and untreated wood products
  • Liquid petroleum products
  • Coal combustion by-products
  • Paper (printed and unprinted) and cardboard
  • Sanitary and medical waste
  • Garbage and landfill waste
  • Asphalt
  • Organic and inorganic fibers
  • Bricks
  • Cinder blocks
  • Concrete
  • Plastic
  • Glass
  • Rubber products
  • Iron and steel

Texture Modifier Terms for Soils with Artifacts

The texture of soils with artifacts is described according to the content of artifacts:

Less than 15 percent.—No texture modifier terms are used.

15 to less than 35 percent.—The term “artifactual” is used, e.g., artifactual loam.

35 to less than 60 percent.—The term “very artifactual” is used, e.g., very artifactual loam.

60 to less than 90 percent.—The term “extremely artifactual” is used, e.g., extremely artifactual loam.

90 percent or more.—No texture modifier terms are used. If there is not enough fine earth to determine the texture class (less than about 10 percent, by volume) the term “artifacts” is used.
 

Compound Texture Modifiers

In some cases, the mineral soil may contain a combination of fragment or composition types for which the use of compound texture modifiers is useful. For example, a soil horizon may contain both artifacts and other fragments, such as rock fragments and pararock fragments. In these cases, the rock fragments, pararock fragments, and artifacts are each described separately. Modifiers for both artifacts and rock or pararock fragments can be combined. The modifier for artifacts comes before the modifier for rock or pararock fragments, e.g., artifactual very gravelly sandy loam. Modifiers for composition and rock fragments can also be combined. For example, a horizon of channery mucky clay or one of gravelly gypsiferous sandy loam contains rock fragments and also a content of high organic matter or gypsum. There are many possible combinations.
 

Fragments on the Surface

This section discusses the description of rock fragments (especially stones and boulders) that are on the soil as opposed to in the soil. The description of gravel, cobbles, and channers (≥ 2 but < mm in diameter) differs from that for stones and boulders (≥ mm in diameter) because an important aspect of gravel, cobbles, and channers is their areal percent cover on the ground surface. This cover provides some protection from wind and water erosion. It may also interfere with seed placement and emergence after germination. For stones and boulders, the percent of cover is not of itself as important as the interference with mechanical manipulation of the soil. For example, a very small areal percentage of large fragments, insignificant for erosion protection, may interfere with tillage, tree harvesting, and other operations involving machinery.

The areal percentage of the ground surface is determined using point-count and/or line-intersect procedures. If the areal percentage equals or exceeds 80 percent, the top of the soil is considered to be the mean height of the top of the rock or pararock fragments. The volume proportions of the 2 to 5 mm, 5 to 75 mm, and 75 to mm fragments should be recorded. This can be done from areal measurements in representative areas.

The number, size, and spacing of stones and boulders (≥ mm in diameter) on the surface of a soil, including both those that lie on the surface and those that are partly within the soil, have important effects on soil use and management. The classes are given in terms of the approximate amount of rock fragments of stone and boulder size at the surface:

Class 1.—Stones or boulders cover to less than percent of the surface. The smallest stones are at least 8 meters apart; the smallest boulders are at least 20 meters apart (fig. ).

Class 2.—Stones or boulders cover to less than 3 percent of the surface. The smallest stones are not less than 1 meter apart; the smallest boulders are not less than 3 meters apart (fig. ).

Class 3.—Stones or boulders cover 3 to less than 15 percent of the surface. The smallest stones are as little as meter apart; the smallest boulders are as little as 1 meter apart (fig. ).

Class 4.—Stones or boulders cover 15 to less than 50 percent of the surface. The smallest stones are as little as meter apart; the smallest boulders are as little as meter apart. In most places it is possible to step from stone to stone or jump from boulder to boulder without touching the soil (fig. ).

Class 5.—Stones or boulders appear to be nearly continuous and cover 50 percent or more of the surface. The smallest stones are less than meter apart; the smallest boulders are less than meter apart. Classifiable soil is among the rock fragments, and plant growth is possible (fig. ).

These limits are intended only as guides to amounts that may mark critical limitations for major kinds of land use. Table is a summary of the classes.

Figure An area of bouldery soil (class 1).Figure An area of very bouldery soil (class 2).Figure An area of extremely bouldery soil (class 3).Figure An area of rubbly soil (class 4).Figure An area of very rubbly soil (class 5).

ClassPercentage of surface coveredDistance in meters between stones or boulders if the diameter is:Descriptive term
m* m m
1 to < ≥ 8≥ 20≥ 37Stony or bouldery
2 to < 1–83–206–37Very stony or very bouldery
3 to < 15–11–32–6Extremely stony or extremely bouldery
415 to < 50–11–2Rubbly
5≥ 50< < < 1Very rubbly

* m if the fragment is flat.
 

Soil Color

Most soil survey organizations, including the National Cooperative Soil Survey in the United States, have adopted the Munsell soil color system for describing soil color (using the elements of hue, value, and chroma). The names associated with each standard color chip (yellowish brown, light gray, etc.) are not strictly part of the Munsell color system. They were selected by the Soil Survey Staff to be used in conjunction with the Munsell color chips. The color chips included in the standard soil-color charts (a subset of all colors in the system) were selected so that soil scientists can describe the normal range of colors found in soils. These chips have enough contrast between them for different individuals to match a soil sample to the same color chip consistently. Interpolating between chips is not recommended in standard soil survey operations because such visual determinations cannot be repeated with a high level of precision. Although digital soil color meters that can provide precise color readings consistently are available, they are not widely used in field operations. Therefore, the standard procedure adopted for soil survey work is visual comparison to the standard soil-color charts.

Elements of Soil Color Descriptions

Elements of soil color descriptions are the color name, the Munsell notation, the water state (moist or dry), and the physical state. An example is “brown (10YR 5/3), dry, crushed and smoothed.” Physical state is recorded as broken, rubbed, crushed, or crushed and smoothed. The term “crushed” typically applies to dry samples and “rubbed” to moist samples. If physical state is unspecified, a broken surface is implied. The color of the soil is normally recorded for a surface broken through a ped, if a ped can be broken as a unit. If ped surfaces are noticeably different in color from the ped interior, this should also be described.

The color value of most soil material is lower after moistening. Consequently, the water state of a sample is always given. The water state is either “moist” or “dry.” The dry state for color determinations is air dry and should be made at the point where the color does not change with additional drying. Color in the moist state is determined on moderately moist or very moist soil material and should be made at the point where the color does not change with additional moistening. The soil should not be moistened to the extent that glistening takes place because the light reflection of water films may cause incorrect color determinations. In a humid region, the moist state generally is standard; in an arid region, the dry state is standard. In detailed descriptions, colors of both dry and moist soil are recorded if feasible. The color for the regionally standard moisture state is typically described first. Both moist and dry colors are valuable, particularly for the immediate surface and tilled horizons, in assessing reflectance.

A Munsell notation is obtained by comparison with a Munsell soil-color chart. The most commonly used charts include only about one fifth of the entire range of hues.1 They consist of about different colored papers, or chips, systematically arranged on hue cards according to their Munsell notations. Figure illustrates the arrangements of color chips on a Munsell color card.

1

Источник: [shoppingdowntown.us]

Polystyrene

Polymer

For other uses, see Polystyrene (disambiguation).

Repeating unit of PS polymer chain
Polystyrene-chain-from-xtal-3D-bspng
shoppingdowntown.us
Names
IUPAC name

Poly(1-phenylethene)

Other names

Thermocol

Identifiers

CAS Number

Abbreviations PS
ChemSpider
ECHA InfoCardEdit this at Wikidata

CompTox Dashboard(EPA)

Properties

Chemical formula

(C8H8)n
Density–&#;g/cm3
Melting point~&#;&#;°C (&#;°F; &#;K)[4] For Isotactic Polystyrene
Boiling point &#;°C (&#;°F; &#;K) and depolymerizes

Solubility in water

Insoluble
SolubilitySoluble in benzene, carbon disulfide, chlorinated aliphatic hydrocarbons, chloroform, cyclohexanone, dioxane, ethyl acetate, ethylbenzene, MEK, NMP, THF [1]
Thermal conductivity W/(m·K) (foam, ρ g/cm3)[2]

Refractive index (nD)

; dielectric constant (1 kHz – 1 GHz)
Related compounds

Related compounds

Styrene (monomer)

Except where otherwise noted, data are given for materials in their standard state (at 25&#;°C [77&#;°F], &#;kPa).

Infobox&#;references

Chemical compound

Expanded polystyrene packaging
A polystyrene yogurt container

Polystyrene (PS) is a synthetic aromatichydrocarbonpolymer made from the monomer known as styrene.[5] Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a poor barrier to oxygen and water vapour and has a relatively low melting point.[6] Polystyrene is one of the most widely used plastics, the scale of its production being several million tonnes per year.[7] Polystyrene can be naturally transparent, but can be coloured with colourants. Uses include protective packaging (such as packing peanuts and in the jewel cases used for storage of optical discs such as CDs and occasionally DVDs), containers, lids, bottles, trays, tumblers, disposablecutlery,[6] in the making of models, and as an alternative material for phonograph records.[8]

As a thermoplastic polymer, polystyrene is in a solid (glassy) state at room temperature but flows if heated above about &#;°C, its glass transition temperature. It becomes rigid again when cooled. This temperature behaviour is exploited for extrusion (as in Styrofoam) and also for molding and vacuum forming, since it can be cast into molds with fine detail.

Under ASTM standards, polystyrene is regarded as not biodegradable. It is accumulating as a form of litter in the outside environment, particularly along shores and waterways, especially in its foam form, and in the Pacific Ocean.[9]

History[edit]

Polystyrene was discovered in by Eduard Simon, an apothecary from Berlin.[10] From storax, the resin of the Oriental sweetgum tree Liquidambar orientalis, he distilled an oily substance, a monomer that he named styrol. Several days later, Simon found that the styrol had thickened into a jelly he dubbed styrol oxide ("Styroloxyd") because he presumed an oxidation. By Jamaican-born chemist John Buddle Blyth and German chemist August Wilhelm von Hofmann showed that the same transformation of styrol took place in the absence of oxygen.[11] They called the product "meta styrol"; analysis showed that it was chemically identical to Simon's Styroloxyd.[12] In Marcellin Berthelot correctly identified the formation of meta styrol/Styroloxyd from styrol as a polymerisation process.[13] About 80 years later it was realized that heating of styrol starts a chain reaction that produces macromolecules, following the thesis of German organic chemist Hermann Staudinger (–). This eventually led to the substance receiving its present name, polystyrene.[citation needed]

The company I. G. Farben began manufacturing polystyrene in Ludwigshafen, about , hoping it would be a suitable replacement for die-cast zinc in many applications. Success was achieved when they developed a reactor vessel that extruded polystyrene through a heated tube and cutter, producing polystyrene in pellet form.[citation needed]

Otis Ray McIntire () a chemical engineer of Dow Chemical rediscovered a process first patented by Swedish inventor Carl Munters.[14] According to the Science History Institute, "Dow bought the rights to Munters’s method and began producing a lightweight, water-resistant, and buoyant material that seemed perfectly suited for building docks and watercraft and for insulating homes, offices, and chicken sheds."[15] In , Styrofoam was patented.[citation needed]

Before , chemical engineer Fritz Stastny (–) developed pre-expanded PS beads by incorporating aliphatic hydrocarbons, such as pentane. These beads are the raw material for molding parts or extruding sheets. BASF and Stastny applied for a patent that was issued in The molding process was demonstrated at the Kunststoff Messe in Düsseldorf. Products were named Styropor.[citation needed]

The crystal structure of isotactic polystyrene was reported by Giulio Natta.[16]

In , the Koppers Company in Pittsburgh, Pennsylvania, developed expanded polystyrene (EPS) foam under the trade name Dylite.[17] In , Dart Container, the largest manufacturer of foam cups, shipped their first order.[18]

Structure[edit]

In chemical terms, polystyrene is a long chain hydrocarbon wherein alternating carbon centers are attached to phenyl groups (a derivative of benzene). Polystyrene's chemical formula is (C
8H
8)
n; it contains the chemical elementscarbon and hydrogen.[citation needed]

The material's properties are determined by short-range van der Waals attractions between polymers chains. Since the molecules consist of thousands of atoms, the cumulative attractive force between the molecules is large. When heated (or deformed at a rapid rate, due to a combination of viscoelastic and thermal insulation properties), the chains can take on a higher degree of confirmation and slide past each other. This intermolecular weakness (versus the high intramolecular strength due to the hydrocarbon backbone) confers flexibility and elasticity. The ability of the system to be readily deformed above its glass transition temperature allows polystyrene (and thermoplastic polymers in general) to be readily softened and molded upon heating. Extruded polystyrene is about as strong as an unalloyed aluminium but much more flexible and much less dense ( g/cm3 for polystyrene vs. g/cm3 for aluminium).[citation needed]

Production[edit]

Polystyrene is an addition polymer that results when styrene monomers interconnect (polymerization). In the polymerization, the carbon-carbon π bond of the vinyl group is broken and a new carbon-carbon σ bond is formed, attaching to the carbon of another styrene monomer to the chain. Since only one kind of monomer is used in its preparation, it is a homopolymer. The newly formed σ bond is stronger than the π bond that was broken, thus it is difficult to depolymerize polystyrene. About a few thousand monomers typically comprise a chain of polystyrene, giving a molecular weight of ,–, g/mol.[citation needed]

Polystyrene shoppingdowntown.us

Each carbon of the backbone has tetrahedral geometry, and those carbons that have a phenyl group (benzene ring) attached are stereogenic. If the backbone were to be laid as a flat elongated zig-zag chain, each phenyl group would be tilted forward or backward compared to the plane of the chain.[citation needed]

The relative stereochemical relationship of consecutive phenyl groups determines the tacticity, which affects various physical properties of the material.[citation needed]

Tacticity[edit]

In polystyrene, tacticity describes the extent to which the phenyl group is uniformly aligned (arranged at one side) in the polymer chain. Tacticity has a strong effect on the properties of the plastic. Standard polystyrene is atactic. The diastereomer where all of the phenyl groups are on the same side is called isotactic polystyrene, which is not produced commercially.[citation needed]

Polystyrene tacticity shoppingdowntown.us

Atactic polystyrene[edit]

The only commercially important form of polystyrene is atactic, in which the phenyl groups are randomly distributed on both sides of the polymer chain. This random positioning prevents the chains from aligning with sufficient regularity to achieve any crystallinity. The plastic has a glass transition temperature Tg of ~90&#;°C. Polymerization is initiated with free radicals.[7]

Syndiotactic polystyrene[edit]

Ziegler–Natta polymerization can produce an ordered syndiotactic polystyrene with the phenyl groups positioned on alternating sides of the hydrocarbon backbone. This form is highly crystalline with a Tm (melting point) of &#;°C (&#;°F). Syndiotactic polystyrene resin is currently produced under the trade name XAREC by Idemitsu corporation, who use a metallocene catalyst for the polymerisation reaction.[19]

Degradation[edit]

Polystyrene is relatively chemically inert. While it is waterproof and resistant to breakdown by many acids and bases, it is easily attacked by many organic solvents (e.g. it dissolves quickly when exposed to acetone), chlorinated solvents, and aromatic hydrocarbon solvents. Because of its resilience and inertness, it is used for fabricating many objects of commerce. Like other organic compounds, polystyrene burns to give carbon dioxide and water vapor, in addition to other thermal degradation by-products. Polystyrene, being an aromatic hydrocarbon, typically combusts incompletely as indicated by the sooty flame.[citation needed]

The process of depolymerizing polystyrene into its monomer, styrene, is called pyrolysis. This involves using high heat and pressure to break down the chemical bonds between each styrene compound. Pyrolysis usually goes up to &#;°C.[20] The high energy cost of doing this has made commercial recycling of polystyrene back into styrene monomer difficult.[citation needed]

Organisms[edit]

Polystyrene is generally considered to be non-biodegradable. However, certain organisms are able to degrade it, albeit very slowly.[21]

In , researchers discovered that mealworms, the larvae form of the darkling beetle Tenebrio molitor, could digest and subsist healthily on a diet of EPS.[22][23] About mealworms could consume between 34 and 39 milligrams of this white foam in a day. The droppings of mealworm were found to be safe for use as soil for crops.[22]

In , it was also reported that superworms (Zophobas morio) may eat expanded polystyrene (EPS).[24] A group of high school students in Ateneo de Manila University found that compared to Tenebrio molitor larvae, Zophobas morio larvae may consume greater amounts of EPS over longer periods of time.[25]

The bacterium Pseudomonas putida is capable of converting styrene oil into the biodegradable plasticPHA.[26][27][28] This may someday be of use in the effective disposing of polystyrene foam. It is worthy to note the polystyrene must undergo pyrolysis to turn into styrene oil.[citation needed]

Forms produced[edit]

Polystyrene is commonly injection molded, vacuum formed, or extruded, while expanded polystyrene is either extruded or molded in a special process. Polystyrene copolymers are also produced; these contain one or more other monomers in addition to styrene. In recent years the expanded polystyrene composites with cellulose[32][33] and starch[34] have also been produced. Polystyrene is used in some polymer-bonded explosives (PBX).[citation needed]

Sheet or molded polystyrene[edit]

CD case made from general purpose polystyrene (GPPS) and high impact polystyrene (HIPS)
Disposable polystyrene razor

Polystyrene (PS) is used for producing disposable plastic cutlery and dinnerware, CD "jewel" cases, smoke detector housings, license plate frames, plastic model assembly kits, and many other objects where a rigid, economical plastic is desired. Production methods include thermoforming (vacuum forming) and injection molding.

Polystyrene Petri dishes and other laboratory containers such as test tubes and microplates play an important role in biomedical research and science. For these uses, articles are almost always made by injection molding, and often sterilized post-molding, either by irradiation or by treatment with ethylene oxide. Post-mold surface modification, usually with oxygen-rich plasmas, is often done to introduce polar groups. Much of modern biomedical research relies on the use of such products; they, therefore, play a critical role in pharmaceutical research.[35]

Thin sheets of polystyrene are used in polystyrene film capacitors as it forms a very stable dielectric, but has largely fallen out of use in favor of polyester.

Foams[edit]

Closeup of expanded polystyrene packaging

Polystyrene foams are % air.[36][37] Polystyrene foams are good thermal insulators and are therefore often used as building insulation materials, such as in insulating concrete forms and structural insulated panel building systems. Grey polystyrene foam, incorporating graphite, has superior insulation properties.[38]

Carl Munters and John Gudbrand Tandberg of Sweden received a US patent for polystyrene foam as an insulation product in (USA patent number 2,,).[39]

PS foams also exhibit good damping properties, therefore it is used widely in packaging. The trademarkStyrofoam by Dow Chemical Company is informally used (mainly US & Canada) for all foamed polystyrene products, although strictly it should only be used for "extruded closed-cell" polystyrene foams made by Dow Chemicals.

Foams are also used for non-weight-bearing architectural structures (such as ornamental pillars).

Expanded polystyrene (EPS)[edit]

Thermocol slabs made of expanded polystyrene (EPS) beads. The one on the left is from a packing box. The one on the right is used for crafts. It has a corky, papery texture and is used for stage decoration, exhibition models, and sometimes as a cheap alternative to shola (Aeschynomene aspera) stems for artwork.
Section of a block of thermocol under a light microscope(bright-field, objective = 10×, eyepiece = 15×). The larger spheres are expanded polystyrene beads which were compressed and fused. The bright, star-shaped hole at the center of the image is an air-gap between the beads where the bead margins have not completely fused. Each bead is made of thin-walled, air-filled bubbles of polystyrene.

Expanded polystyrene (EPS) is a rigid and tough, closed-cell foam with a normal density range of 11 to 32&#;kg/m3.[40] It is usually white and made of pre-expanded polystyrene beads. The manufacturing process for EPS conventionally begins with the creation of small polystyrene beads. Styrene monomers (and potentially other additives) are suspended in water, where they undergo free-radical addition polymerization. The polystyrene beads formed by this mechanism may have an average diameter of around &#;μm. The beads are then permeated with a "blowing agent", a material that enables the beads to be expanded. Pentane is commonly used as the blowing agent. The beads are added to a continuously agitated reactor with the blowing agent, among other additives, and the blowing agent seeps into pores within each bead. The beads are then expanded using steam.[41]

EPS is used for food containers, molded sheets for building insulation, and packing material either as solid blocks formed to accommodate the item being protected or as loose-fill "peanuts"cushioning fragile items inside boxes. EPS also has been widely used in automotive and road safety applications such as motorcycle helmets and road barriers on automobile race tracks.[42][43][44]

A significant portion of all EPS products are manufactured through injection molding. Mold tools tend to be manufactured from steels (which can be hardened and plated), and aluminum alloys. The molds are controlled through a split via a channel system of gates and runners.[45] EPS is colloquially called "styrofoam" in the United States and Canada, an incorrectly applied genericization of Dow Chemical's brand of extruded polystyrene.[46]

EPS in building construction[edit]

Sheets of EPS are commonly packaged as rigid panels (Common in Europe is a size of &#;cm x 50&#;cm, usually depending on an intended type of connection and glue techniques, it is, in fact, &#;cm x &#;cm or 98&#;cm x 48&#;cm; less common is x 60&#;cm; size 4 by 8&#;ft ( by &#;m) or 2 by 8&#;ft ( by &#;m) in the United States). Common thicknesses are from 10&#;mm to &#;mm. Many customizations, additives, and thin additional external layers on one or both sides are often added to help with various properties.

Thermal conductivity is measured according to EN Typical values range from to &#;W/(m⋅K) depending on the density of the EPS board. The value of &#;W/(m⋅K) was obtained at 15&#;kg/m3 while the value of &#;W/(m⋅K) was obtained at 40&#;kg/m3 according to the datasheet of K from StyroChem Finland. Adding fillers (graphites, aluminum, or carbons) has recently allowed the thermal conductivity of EPS to reach around –&#;W/(m⋅K) (as low as &#;W/(m⋅K)) and as such has a grey/black color which distinguishes it from standard EPS. Several EPS producers have produced a variety of these increased thermal resistance EPS usage for this product in the UK and EU.

Water vapor diffusion resistance (μ) of EPS is around 30–

ICC-ES (International Code Council Evaluation Service) requires EPS boards used in building construction meet ASTM C requirements. One of these requirements is that the limiting oxygen index of EPS as measured by ASTM D be greater than 24 volume&#;%. Typical EPS has an oxygen index of around 18 volume&#;%; thus, a flame retardant is added to styrene or polystyrene during the formation of EPS.

The boards containing a flame retardant when tested in a tunnel using test method UL or ASTM E84 will have a flame spread index of less than 25 and a smoke-developed index of less than ICC-ES requires the use of a minute thermal barrier when EPS boards are used inside of a building.

According to the EPS-IA ICF organization, the typical density of EPS used for insulated concrete forms (expanded polystyrene concrete) is to pounds per cubic foot ( to &#;kg/m3). This is either Type II or Type IX EPS according to ASTM C EPS blocks or boards used in building construction are commonly cut using hot wires.[47]

Extruded polystyrene (XPS)[edit]

Extruded polystyrene foam (XPS) consists of closed cells. It offers improved surface roughness, higher stiffness and reduced thermal conductivity. The density range is about 28–45&#;kg/m3.[citation needed]

Extruded polystyrene material is also used in crafts and model building, in particular architectural models. Because of the extrusion manufacturing process, XPS does not require facers to maintain its thermal or physical property performance. Thus, it makes a more uniform substitute for corrugated cardboard. Thermal conductivity varies between and W/(m·K) depending on bearing strength/density and the average value is ~ W/(m·K).

Water vapor diffusion resistance (μ) of XPS is around 80–

Commonly extruded polystyrene foam materials include:

Water absorption of polystyrene foams[edit]

Although it is a closed-cell foam, both expanded and extruded polystyrene are not entirely waterproof or vapor proof.[49] In expanded polystyrene there are interstitial gaps between the expanded closed-cell pellets that form an open network of channels between the bonded pellets, and this network of gaps can become filled with liquid water. If the water freezes into ice, it expands and can cause polystyrene pellets to break off from the foam. Extruded polystyrene is also permeable by water molecules and can not be considered a vapor barrier.[50]

Water-logging commonly occurs over a long period in polystyrene foams that are constantly exposed to high humidity or are continuously immersed in water, such as in hot tub covers, in floating docks, as supplemental flotation under boat seats, and for below-grade exterior building insulation constantly exposed to groundwater.[51] Typically an exterior vapor barrier such as impermeable plastic sheeting or a sprayed-on coating is necessary to prevent saturation.

Oriented polystyrene[edit]

Oriented polystyrene (OPS) is produced by stretching extruded PS film, improving visibility through the material by reducing haziness and increasing stiffness. This is often used in packaging where the manufacturer would like the consumer to see the enclosed product. Some benefits to OPS are that it is less expensive to produce than other clear plastics such as polypropylene (PP), (PET), and high-impact polystyrene (HIPS), and it is less hazy than HIPS or PP. The main disadvantage of OPS is that it is brittle, and will crack or tear easily.

Co-polymers[edit]

Ordinary (homopolymeric) polystyrene has an excellent property profile about transparency, surface quality and stiffness. Its range of applications is further extended by copolymerization and other modifications (blends e.g. with PC and syndiotactic polystyrene).[52]:&#;–&#; Several copolymers are used based on styrene: The crispiness of homopolymeric polystyrene is overcome by elastomer-modified styrene-butadiene copolymers. Copolymers of styrene and acrylonitrile (SAN) are more resistant to thermal stress, heat and chemicals than homopolymers and are also transparent. Copolymers called ABS have similar properties and can be used at low temperatures, but they are opaque.

Styrene-butane co-polymers[edit]

Styrene-butane co-polymers can be produced with a low butene content. Styrene-butane co-polymers include PS-I and SBC (see below), both co-polymers are impact resistant. PS-I is prepared by graft co-polymerization, SBC by anionic block co-polymerization, which makes it transparent in case of appropriate block size.[53]

If styrene-butane co-polymer has a high butylene content, styrene-butadiene rubber (SBR) is formed.

The impact strength of styrene-butadiene co-polymers is based on phase separation, polystyrene and poly-butane are not soluble in each other (see Flory-Huggins theory). Co-polymerization creates a boundary layer without complete mixing. The butadiene fractions (the "rubber phase") assemble to form particles embedded in a polystyrene matrix. A decisive factor for the improved impact strength of styrene-butadiene copolymers is their higher absorption capacity for deformation work. Without applied force, the rubber phase initially behaves like a filler. Under tensile stress, crazes (microcracks) are formed, which spread to the rubber particles. The energy of the propagating crack is then transferred to the rubber particles along its path. A large number of cracks give the originally rigid material a laminated structure. The formation of each lamella contributes to the consumption of energy and thus to an increase in elongation at break. Polystyrene homo-polymers deform when a force is applied until they break. Styrene-butane co-polymers do not break at this point, but begin to flow, solidify to tensile strength and only break at much higher elongation.[54]:&#;&#;

With a high proportion of polybutadiene, the effect of the two phases is reversed. Styrene-butadiene rubber behaves like an elastomer but can be processed like a thermoplastic.

Impact-resistant polystyrene (PS-I)[edit]

PS-I (impact resistant polystyrene) consists of a continuous polystyrene matrix and a rubber phase dispersed therein. It is produced by polymerization of styrene in the presence of polybutadiene dissolved (in styrene). Polymerization takes place simultaneously in two ways:[55]

  • Graft copolymerization: The growing polystyrene chain reacts with a double bond of the polybutadiene. As a result, several polystyrene chains are attached to one polybutadien S represents in the figure the styrene repeat unit, B the butadiene repeat unit. However, the middle block often does not consist of such depicted butane homo-polymer but of a styrene-butadiene co-polymer:

SSSSSS&#;SSSSSSS&#;SSSSSSBBSBBSB&#;SBBBBSB&#;SSBBBSBSSSSSSS&#;SSSSSSS&#;SSSSSSSSSSSSSSSS

By using a statistical copolymer at this position, the polymer becomes less susceptible to cross-linking and flows better in the melt. For the production of SBS, the first styrene is homopolymerized via anionic copolymerization. Typically, an organometallic compound such as butyllithium is used as a catalyst. Butadiene is then added and after styrene again its polymerization. The catalyst remains active during the whole process (for which the used chemicals must be of high purity). The molecular weight distribution of the polymers is very low (polydispersity in the range of , the individual chains have thus very similar lengths). The length of the individual blocks can be adjusted by the ratio of catalyst to monomer. The size of the rubber sections, in turn, depends on the block length. The production of small structures (smaller than the wavelength of the light) ensure transparency. In contrast to PS-I, however, the block copolymer does not form any particles but has a lamellar structure.

Styrene-butadiene rubber[edit]

Main article: Styrene-butadiene

Styrene-butadiene rubber (SBR) is produced like PS-I by graft copolymerization, but with a lower styrene content. Styrene-butadiene rubber thus consists of a rubber matrix with a polystyrene phase dispersed therein.[56] Unlike PS-I and SBC, it is not a thermoplastic, but an elastomer. Within the rubber phase, the polystyrene phase is assembled into domains. This causes physical cross-linking on a microscopic level. When the material is heated above the glass transition point, the domains disintegrate, the cross-linking is temporarily suspended and the material can be processed like a thermoplastic.[57]

Acrylonitrile butadiene styrene[edit]

Main article: Acrylonitrile butadiene styrene

Acrylonitrile butadiene styrene (ABS) is a material that is stronger than pure polystyrene.

Others[edit]

SMA is a copolymer with maleic anhydride. Styrene can be copolymerized with other monomers; for example, divinylbenzene can be used for cross-linking the polystyrene chains to give the polymer used in solid phase peptide synthesis. Styrene-acrylonitrile resin (SAN) has a greater thermal resistance than pure styrene.

Environmental issues[edit]

Production[edit]

Polystyrene foams are produced using blowing agents that form bubbles and expand the foam. In expanded polystyrene, these are usually hydrocarbons such as pentane, which may pose a flammability hazard in manufacturing or storage of newly manufactured material, but have relatively mild environmental impact.[citation needed] Extruded polystyrene is usually made with hydrofluorocarbons (HFCa),[58] which have global warming potentials of approximately – times that of carbon dioxide.[59]

Non-biodegradable[edit]

Waste polystyrene takes hundreds of years to biodegrade and is resistant to photo-oxidation.[60]

Litter[edit]

  • Coastal debris including polystyrene

Animals do not recognize polystyrene foam as an artificial material and may even mistake it for food.[61] Polystyrene foam blows in the wind and floats on water, due to its low specific gravity. It can have serious effects on the health of birds or marine animals that swallow significant quantities.[61] Juvenile rainbow trout exposed to polystyrene fragments have produced toxic effects by causing substantial histomorphometrical changes.[62]

Reducing[edit]

Main article: Phase-out of polystyrene foam

Restricting the use of foamed polystyrene takeout food packaging is a priority of many solid waste environmental organisations.[63] Efforts have been made to find alternatives to polystyrene, especially foam in restaurant settings. The original impetus was to eliminate chlorofluorocarbons (CFC), which was a former component of foam.

United States[edit]

In , Berkeley, California, banned CFC food containers.[64] The following year, Suffolk County, New York, became the first U.S. jurisdiction to ban polystyrene in general.[65] However, legal challenges by the Society of the Plastics Industry[66] kept the ban from going into effect until at last it was delayed when the Republican and Conservative parties gained the majority of the county legislature.[67] In the meantime, Berkeley became the first city to ban all foam food containers.[68] As of , about one hundred localities in the United States, including Portland, Oregon, and San Francisco had some sort of ban on polystyrene foam in restaurants. For instance, in Oakland, California, required restaurants to switch to disposable food containers that would biodegrade if added to food compost.[69] In , San Jose became reportedly the largest city in the country to ban polystyrene foam food containers.[70] Some communities have implemented wide polystyrene bans, such as Freeport, Maine, which did so in [71] In , the first U.S. ban of general polystyrene foam was enacted in Berkeley, California.[68]

On 1 July , New York City became the largest city in the United States to attempt to prohibit the sale, possession, and distribution of single-use polystyrene foam (the initial decision was overturned on appeal).[72] In San Francisco, supervisors approved the toughest ban on "Styrofoam" (EPS) in the US which went into effect 1 January The city's Department of the Environment can make exceptions for certain uses like shipping medicines at prescribed temperatures.[73]

The U.S. Green Restaurant Association does not allow polystyrene foam to be used as part of its certification standard.[74] Several green leaders, from the Dutch Ministry of the Environment to Starbucks's Green Team, advise people to reduce their environmental harm by using reusable coffee cups.[75]

In March , Maryland banned polystyrene foam food containers and became the first state in the country to pass a food container foam ban through the state legislature. Maine was the first state to officially get a foam food container ban onto the books. In May , Maryland Governor Hogan allowed the foam ban (House Bill ) to become law without a signature making Maryland the second state to have a food container foam ban on the books, but is the first one to take effect on 1 July [76][77][78][79]

In September , the New Jersey state legislature voted to ban disposable foam food containers and cups made of polystyrene foam.[80]

[edit]

China banned expanded polystyrene takeout/takeaway containers and tableware around However, compliance has been a problem and, in , the Chinese plastics industry was lobbying for the ban's repeal.[81]

India and Taiwan also banned polystyrene-foam food-service ware before [82]

The government of Zimbabwe, through its Environmental Management Agency (EMA), banned polystyrene containers (popularly called 'kaylite' in the country), under Statutory Instrument 84 of (Plastic Packaging and Plastic Bottles) (Amendment) Regulations, (No 1.) [83][84]

The city of Vancouver, Canada, has announced its Zero Waste plan in The city will introduce bylaw amendments to prohibit business license holders from serving prepared food in polystyrene foam cups and take-out containers, beginning 1 June [85]

Fiji passed the Environmental Management Bill in December Imports of polystyrene products was banned in January [86]

Recycling[edit]

In general, polystyrene is not accepted in curbside collection recycling programs and is not separated and recycled where it is accepted. In Germany, polystyrene is collected, as a consequence of the packaging law (Verpackungsverordnung) that requires manufacturers to take responsibility for recycling or disposing of any packaging material they sell.

Most polystyrene products are currently not recycled due to the lack of incentive to invest in the compactors and logistical systems required. Due to the low density of polystyrene foam, it is not economical to collect. However, if the waste material goes through an initial compaction process, the material changes density from typically 30&#;kg/m3 to &#;kg/m3 and becomes a recyclable commodity of high value for producers of recycled plastic pellets. Expanded polystyrene scrap can be easily added to products such as EPS insulation sheets and other EPS materials for construction applications; many manufacturers cannot obtain sufficient scrap because of collection issues. When it is not used to make more EPS, foam scrap can be turned into products such as clothes hangers, park benches, flower pots, toys, rulers, stapler bodies, seedling containers, picture frames, and architectural molding from recycled PS.[87] As of , around tonnes of EPS are recycled every month in the UK.[88]

Recycled EPS is also used in many metal casting operations. Rastra is made from EPS that is combined with cement to be used as an insulating amendment in the making of concrete foundations and walls. American manufacturers have produced insulating concrete forms made with approximately 80% recycled EPS since

Incineration[edit]

If polystyrene is properly incinerated at high temperatures (up to &#;°C[89]) and with plenty of air[89] (14 m3/kg[citation needed]), the chemicals generated are water, carbon dioxide, and possibly small amounts of residual halogen-compounds from flame-retardants.[89] If only incomplete incineration is done, there will also be leftover carbon soot and a complex mixture of volatile compounds.[90][better&#;source&#;needed] According to the American Chemistry Council, when polystyrene is incinerated in modern facilities, the final volume is 1% of the starting volume; most of the polystyrene is converted into carbon dioxide, water vapor, and heat. Because of the amount of heat released, it is sometimes used as a power source for steam or electricity generation.[89][91]

When polystyrene was burned at temperatures of –&#;°C (the typical range of a modern incinerator), the products of combustion consisted of "a complex mixture of polycyclic aromatic hydrocarbons (PAHs) from alkyl benzenes to benzoperylene. Over 90 different compounds were identified in combustion effluents from polystyrene."[92][better&#;source&#;needed] The American National Bureau of Standards Center for Fire Research found 57 chemical by-products released during the combustion of expanded polystyrene (EPS) foam.[93]

Safety[edit]

Health[edit]

The American Chemistry Council, formerly known as the Chemical Manufacturers' Association, writes:

Based on scientific tests over five decades, government safety agencies have determined that polystyrene is safe for use in foodservice products. For example, polystyrene meets the stringent standards of the U.S. Food and Drug Administration and the European Commission/European Food Safety Authority for use in packaging to store and serve food. The Hong Kong Food and Environmental Hygiene Department recently reviewed the safety of serving various foods in polystyrene foodservice products and reached the same conclusion as the U.S. FDA.[94]

From to , a comprehensive review of the potential health risks associated with exposure to styrene was conducted by a member international expert panel selected by the Harvard Center for Risk Assessment. The scientists had expertise in toxicology, epidemiology, medicine, risk analysis, pharmacokinetics, and exposure assessment. The Harvard study reported that styrene is naturally present in trace quantities in foods such as strawberries, beef, and spices, and is naturally produced in the processing of foods such as wine and cheese. The study also reviewed all the published data on the quantity of styrene contributing to the diet due to migration of food packaging and disposable food contact articles, and concluded that risk to the general public from exposure to styrene from foods or food-contact applications (such as polystyrene packaging and foodservice containers) was at levels too low to produce adverse effects.[95]

Polystyrene is commonly used in containers for food and drinks. The styrene monomer (from which polystyrene is made) is a cancer suspect agent.[96] Styrene is "generally found in such low levels in consumer products that risks aren't substantial".[97] Polystyrene which is used for food contact may not contain more than 1% (% for fatty foods) of styrene by weight.[98] Styrene oligomers in polystyrene containers used for food packaging have been found to migrate into the food.[99] Another Japanese study conducted on wild-type and AhR-null mice found that the styrene trimer, which the authors detected in cooked polystyrene container-packed instant foods, may increase thyroid hormone levels.[]

Whether polystyrene can be microwaved with food is controversial. Some containers may be safely used in a microwave, but only if labeled as such.[] Some sources suggest that foods containing carotene (vitamin A) or cooking oils must be avoided.[]

Because of the pervasive use of polystyrene, these serious health related issues remain topical.[]

Fire hazards[edit]

Like other organic compounds, polystyrene is flammable. Polystyrene is classified according to DIN as a "B3" product, meaning highly inflammable or "Easily Ignited." As a consequence, although it is an efficient insulator at low temperatures, its use is prohibited in any exposed installations in building construction if the material is not flame-retardant.[citation needed] It must be concealed behind drywall, sheet metal, or concrete.[] Foamed polystyrene plastic materials have been accidentally ignited and caused huge fires and losses of life, for example at the Düsseldorf International Airport and in the Channel Tunnel (where polystyrene was inside a railway carriage that caught fire).[]

See also[edit]

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  59. ^Bandyopadhyay, A.; Basak, G. Chandra (). "Studies on photocatalytic degradation of polystyrene". Materials Science and Technology. 23 (3): – doi/X S2CID&#;
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  61. ^Karbalaei, Samaneh; Hanachi, Parichehr; Rafiee, Gholamreza; Seifori, Parvaneh; Walker, Tony R. (September ). "Toxicity of polystyrene microplastics on juvenile Oncorhynchus mykiss (rainbow trout) after individual and combined exposure with chlorpyrifos". Journal of Hazardous Materials. : doi/shoppingdowntown.ust PMID&#; S2CID&#;
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Источник: [shoppingdowntown.us]

Instagram

American photo and video sharing social networking service

"Insta" redirects here. For the food delivery service, see Instacart. For the song by Dimitri Vegas & Like Mike, see Instagram (song).

Instagram[a] is an American photo and video sharingsocial networking service founded by Kevin Systrom and Mike Krieger. In April , Facebook Inc. acquired the service for approximately US$1&#;billion in cash and stock. The app allows users to upload media that can be edited with filters and organized by hashtags and geographical tagging. Posts can be shared publicly or with pre-approved followers. Users can browse other users' content by tags and locations and view trending content. Users can like photos and follow other users to add their content to a personal feed.[10]

Instagram was originally distinguished by only allowing content to be framed in a square () aspect ratio with pixels to match the display width of the iPhone at the time. In , these restrictions were eased with an increase to pixels. The service also added messaging features, the ability to include multiple images or videos in a single post, and a 'stories' feature—similar to its main opposition Snapchat—which allows users to post photos and videos to a sequential feed, with each post accessible by others for 24 hours each. As of January , the Stories feature is used by &#;million users daily.[10]

Originally launched for iOS in October , Instagram rapidly gained popularity, with one million registered users in two months, 10&#;million in a year, and 1&#;billion as of June [11] The Android version was released in April , followed by a feature-limited desktop interface in November , a Fire OS app in June , and an app for Windows 10 in October As of October&#;[update], over 40&#;billion photos had been uploaded. Although praised for its influence, Instagram has been the subject of criticism, most notably for the negative impact on teens' mental health, policy and interface changes, allegations of censorship, and illegal or improper content uploaded by users.

As of June , the most followed person is Portuguese professional footballer Cristiano Ronaldo with over &#;million followers.[12]

As of January 14, , the most-liked photo on Instagram is a picture of an egg, posted by the account @world_record_egg, created with the sole purpose of surpassing the previous record of 18&#;million likes on a Kylie Jenner post. The picture currently has over 55&#;million likes.[13] The second most-liked photo is a wedding photo of Ariana Grande and her husband Dalton Gomez.[14] Instagram was the fourth most downloaded mobile app of the s.[12]

History

Instagram Icon since

See also: Timeline of Instagram

Instagram began development in San Francisco as Burbn, a mobile check-in app created by Kevin Systrom and Mike Krieger.[15] Realizing that Burbn was too similar to Foursquare, Systrom and Krieger refocused their app on photo-sharing, which had become a popular feature among Burbn users.[16][17] They renamed the app Instagram, a portmanteau of "instant camera" and "telegram".[18]

– Beginnings and major funding

On March 5, , Systrom closed a $, seed funding round with Baseline Ventures and Andreessen Horowitz while working on Burbn.[19] Josh Riedel joined the company in October as Community Manager,[20] Shayne Sweeney joined in November as an engineer,[20] and Jessica Zollman joined as a Community Evangelist in August [20][21]

The first Instagram post was a photo of South Beach Harbor at Pier 38, posted by Mike Krieger at PM on July 16, [22][17] Systrom shared his first post, a picture of a dog and his girlfriend's foot, a few hours later at PM. It has been wrongly attributed as the first Instagram photo due to the earlier letter of the alphabet in its URL.[23][24][better&#;source&#;needed] On October 6, , the Instagram iOS app was officially released through the App Store.[25]

In February , it was reported that Instagram had raised $7&#;million in Series A funding from a variety of investors, including Benchmark Capital, Jack Dorsey, Chris Sacca (through Capital fund), and Adam D'Angelo.[26] The deal valued Instagram at around $20&#;million.[27] In April , Instagram raised $50&#;million from venture capitalists with a $&#;million valuation.[28]Joshua Kushner was the second largest investor in Instagram's Series B fundraising round, leading his investment firm, Thrive Capital, to double its money after the sale to Facebook.[29]

– Additional platforms and acquisition by Facebook

On April 3, , Instagram released a version of its app for Android phones,[30][31] and it was downloaded more than one million times in less than one day.[32] The Android app has since received two significant updates: first, in March , which cut the file size of the app by half and added performance improvements;[33][34] then in April , to add an offline mode that allows users to view and interact with content without an Internet connection. At the time of the announcement, it was reported that 80% of Instagram's &#;million users were located outside the U.S., and while the aforementioned functionality was live at its announcement, Instagram also announced its intention to make more features available offline, and that they were "exploring an iOS version".[35][36][37]

On April 9, , Facebook, Inc. bought Instagram for $1&#;billion in cash and stock,[38][39][40] with a plan to keep the company independently managed.[41][42][43] Britain's Office of Fair Trading approved the deal on August 14, ,[44] and on August 22, , the Federal Trade Commission in the U.S. closed its investigation, allowing the deal to proceed.[45] On September 6, , the deal between Instagram and Facebook officially closed with a purchase price of $&#;million in cash and 23&#;million shares of stock.[46]

The deal closed just before Facebook's scheduled initial public offering according to CNN.[43] The deal price was compared to the $35&#;million Yahoo! paid for Flickr in [43]Mark Zuckerberg said Facebook was "committed to building and growing Instagram independently."[43] According to Wired, the deal netted Systrom $&#;million.[47]

In November , Instagram launched website profiles, allowing anyone to see user feeds from a web browser with limited functionality,[48] as well as a selection of badges, web widget buttons to link to profiles.[49]

Since the app's launch it had used the Foursquare API technology to provide named location tagging. In March , Instagram started to test and switch the technology to use Facebook Places.[50][51]

– Redesign and Windows app

In June , the desktop website user interface was redesigned to become more flat and minimalistic, but with more screen space for each photo and to resemble the layout of Instagram's mobile website.[52][53][54] Furthermore, one row of pictures only has three instead of five photos to match the mobile layout. The slideshow banner[55][56] on the top of profile pages, which simultaneously slide-showed seven picture tiles of pictures posted by the user, alternating at different times in a random order, has been removed. In addition, the formerly angular profile pictures became circular.

On May 11, , Instagram revamped its design, adding a black-and-white flat design theme for the app's user interface, and a less skeuomorphistic, more abstract, "modern" and colorful icon.[57][58][59] Rumors of a redesign first started circulating in April, when The Verge received a screenshot from a tipster, but at the time, an Instagram spokesperson simply told the publication that it was only a concept.[60]

On December 6, , Instagram introduced comment liking. However, unlike post likes, the user who posted a comment does not receive notifications about comment likes in their notification inbox. Uploaders can optionally decide to deactivate comments on a post.[61][62][63]

In April , Instagram released a Windows 10 Mobile app, after years of demand from Microsoft and the public to release an app for the platform.[64][65] The platform previously had a beta version of Instagram, first released on November 21, , for Windows Phone 8.[66][67][68] The new app added support for videos (viewing and creating posts or stories, and viewing live streams), album posts and direct messages.[69] Similarly, an app for Windows 10 personal computers and tablets was released in October [70][71] In May, Instagram updated its mobile website to allow users to upload photos, and to add a "lightweight" version of the Explore tab.[72][73]

The mobile web front end allows uploading pictures since May 4, Image filters and the ability to upload videos were not introduced then.[74][75]

On April 30, , the Windows 10 Mobile app was discontinued, though the mobile website remains available as a progressive web application (PWA) with limited functionality. The app remains available on Windows 10 computers and tablets, also updated to a PWA in

– IGTV, removal of the like counter, management changes

To comply with the GDPR regulations regarding data portability, Instagram introduced the ability for users to download an archive of their user data in April [76][77][78]

IGTV launched on June 20, , as a standalone video application.

On September 24, , Krieger and Systrom announced in a statement they would be stepping down from Instagram.[79][80] On October 1, , it was announced that Adam Mosseri would be the new head of Instagram.[81][82]

During Facebook F8, it was announced that Instagram would, beginning in Canada, pilot the removal of publicly-displayed "like" counts for content posted by other users.[83] Like counts would only be visible to the user who originally posted the content. Mosseri stated that this was intended to have users "worry a little bit less about how many likes they're getting on Instagram and spend a bit more time connecting with the people that they care about."[84][85] It has been argued that low numbers of likes in relativity to others could contribute to a lower self-esteem in users.[85][83] The pilot began in May , and was extended to 6 other markets in July.[85][86] The pilot was expanded worldwide in November [87] Also in July , Instagram announced that it would implement new features designed to reduce harassment and negative comments on the service.[88]

In August , Instagram also began to pilot the removal of the "Following" tab from the app, which had allowed users to view a feed of the likes and comments made by users they follow. The change was made official in October, with head of product Vishal Shah stating that the feature was underused and that some users were "surprised" when they realized their activity was being surfaced in this manner.[89][90]

In October , Instagram introduced a limit on the number of posts visible in page scrolling mode unless logged in. Until this point, public profiles had been available to all users, even when not logged in. Following the change, after viewing a number of posts a pop-up requires the user to log in to continue viewing content.[91][92][93]

–present: New features

In March , Instagram launched a new feature called "Co-Watching". The new feature allows users to share posts with each other over video calls. According to Instagram, they pushed forward the launch of Co-Watching in order to meet the demand for virtually connecting with friends and family due to social distancing as a result of the COVID pandemic.[94]

In August , Instagram launched a new feature called "Reels". The feature is similar to TikTok.[95] Instagram also added suggested posts in August After scrolling through posts from the past 48 hours, Instagram displays posts related to their interests from accounts they do not follow.[96]

In February , Instagram began testing a new feature called Vertical Stories, said by some sources to be inspired by TikTok.[97] The same month, they also began testing the removal of ability to share feed posts to stories.[98]

In March , Instagram launched a new feature in which four people can go live at once.[99] Instagram also announced that adults would not be allowed to message teens who don't follow them as part of a series of new child safety policies.[][][][]

In May , Instagram began allowing users in some regions to add pronouns to their profile page.[][]

On October 4, , Facebook had its worst outage since The outage also affected other platforms owned by Facebook, such as Instagram and WhatsApp.[][] Security experts identified the problem as possibly being DNS-related.[]

Negative effect on teenage girls’ mental health

Facebook has known for years that its Instagram app is harmful to a number of teenagers, according to research seen by the Wall Street Journal, but the company concealed the knowledge from lawmakers.[]

Internal Facebook presentations seen by the WSJ in show that Instagram is toxic to a sizable percentage of its users, particularly teenage girls. More than 40% of Instagram’s users are under 23 years old.

“We make body image issues worse for one in three teen girls,” said a slide from a presentation. “Teens blame Instagram for increases in the rate of anxiety and depression,” said another. “This reaction was unprompted and consistent across all groups.”

The presentations were seen by the company’s executives and the findings mentioned to Mark Zuckerberg in But when asked in March about Instagram’s effect on young people, Zuckerberg defended the company’s plan to launch an Instagram product for children under

When asked by senators for its internal findings on the impact of Instagram on youth mental health, Facebook sent a six-page letter but did not include the company’s research. The company told Forbes its research is “kept confidential to promote frank and open dialogue and brainstorming internally.”[]

In a blog post, Instagram said the WSJ story "focuses on a limited set of findings and casts them in a negative light."[]

On September 27, , weeks after the WSJ report was released, Facebook announced it "paused" development of Instagram Kids, the Instagram product aimed at children. The company stated it was looking into concerns raised by the regulators and parents. Adam Mosseri stated that the company would return to the project as "[t]he reality is that kids are already online, and we believe that developing age-appropriate experiences designed specifically for them is far better for parents than where we are today."[][]

Features and tools

An original photograph (left) is automatically cropped to a square by Instagram, and has a filter added at the selection of the user (right).
A photo collage of an unprocessed image (top left) modified with the 16 different Instagram filtersavailable in

Users can upload photographs and short videos, follow other users' feeds,[] and geotag images with the name of a location.[] Users can set their account as "private", thereby requiring that they approve any new follower requests.[] Users can connect their Instagram account to other social networking sites, enabling them to share uploaded photos to those sites.[] In September , a new version of the app included new and live filters, instant tilt–shift, high-resolution photographs, optional borders, one-click rotation, and an updated icon.[][] Photos were initially restricted to a square, aspect ratio; since August , the app supports portrait and widescreen aspect ratios as well.[][][] Users could formerly view a map of a user's geotagged photos. The feature was removed in September , citing low usage.[][]

Since December , posts can be "saved" into a private area of the app.[][] The feature was updated in April to let users organize saved posts into named collections.[][] Users can also "archive" their posts in a private storage area, out of visibility for the public and other users. The move was seen as a way to prevent users from deleting photos that don't garner a desired number of "likes" or are deemed boring, but also as a way to limit the "emergent behavior" of deleting photos, which deprives the service of content.[][] In August, Instagram announced that it would start organizing comments into threads, letting users more easily interact with replies.[][]

Since February , up to ten pictures or videos can be included in a single post, with the content appearing as a swipeable carousel.[][] The feature originally limited photos to the square format, but received an update in August to enable portrait and landscape photos instead.[][]

In April , Instagram launched its version of a portrait mode called "focus mode," which gently blurs the background of a photo or video while keeping the subject in focus when selected.[] In November, Instagram began to support Alt text to add descriptions of photos for the visually impaired. They are either generated automatically using object recognition (using existing Facebook technology) or manually specified by the uploader.[]

On March 1, , Instagram launched a new feature named Instagram Live "Rooms" Let Four People Go Live Together.[]

In May , Instagram announced a new accessibility feature for videos on Instagram Reels and Stories to allow creators to place closed captions on their content.[]

Hashtags

In January , Instagram introduced hashtags to help users discover both photos and each other.[][] Instagram encourages users to make tags both specific and relevant, rather than tagging generic words like "photo", to make photographs stand out and to attract like-minded Instagram users.[]

Users on Instagram have created "trends" through hashtags. The trends deemed the most popular on the platform often highlight a specific day of the week to post the material on. Examples of popular trends include #SelfieSunday, in which users post a photo of their faces on Sundays; #MotivationMonday, in which users post motivational photos on Mondays; #TransformationTuesday, in which users post photos highlighting differences from the past to the present; #WomanCrushWednesday, in which users post photos of women they have a romantic interest in or view favorably, as well as its #ManCrushMonday counterpart centered on men; and #ThrowbackThursday, in which users post a photo from their past, highlighting a particular moment.[][]

In December , Instagram began to allow users to follow hashtags, which display relevant highlights of the topic in their feeds.[][]

Explore

In June , Instagram introduced "Explore", a tab inside the app that displays popular photos, photos taken at nearby locations, and search.[] The tab was updated in June to feature trending tags and places, curated content, and the ability to search for locations.[] In April , Instagram added a "Videos You Might Like" channel to the tab,[][] followed by an "Events" channel in August, featuring videos from concerts, sports games, and other live events,[][] followed by the addition of Instagram Stories in October.[][] The tab was later expanded again in November after Instagram Live launched to display an algorithmically-curated page of the "best" Instagram Live videos currently airing.[] In May , Instagram once again updated the Explore tab to promote public Stories content from nearby places.[]

Photographic filters

Instagram offers a number of photographic filters that users can apply to their images. In February , Instagram added a "Lux" filter, an effect that "lightens shadows, darkens highlights and increases contrast".[][] In December , Slumber, Crema, Ludwig, Aden, and Perpetua were five new filters to be added to the Instagram filter family.[]

Video

Initially a purely photo-sharing service, Instagram incorporated second video sharing in June [][] The addition was seen by some in the technology media as Facebook's attempt at competing with the then-popular video-sharing application Vine.[][] In August , Instagram added support for widescreen videos.[][] In March , Instagram increased the second video limit to 60 seconds.[][] Albums were introduced in February , which allow up to 10 minutes of video to be shared in one post.[][][]

IGTV

Main article: IGTV

IGTV is a vertical video&#;application launched by Instagram[] in June Basic functionality is also available within the Instagram app and website. IGTV allows uploads of up to 10 minutes in length with a file size of up to MB, with verified and popular users allowed to upload videos of up to 60 minutes in length with a file size of up to GB.[] The app automatically begins playing videos as soon as it is launched, which CEO Kevin Systrom contrasted to video hosts where one must first locate a video.[][][]

Reels

In November , it was reported that Instagram had begun to pilot a new video feature known as "Reels" in Brazil, expanding to France and Germany afterwards.[] It is similar in functionality to the Chinese video-sharing service TikTok, with a focus on allowing users to record short videos set to pre-existing sound clips from other posts.[] Users could make up to 15 (later 30) second videos using this feature.[] Reels also integrates with existing Instagram filters and editing tools.[]

In July , Instagram rolled out Reels to India after TikTok was banned in the country.[] The following month, Reels officially launched in 50 countries including the United States, Canada and United Kingdom.[] Instagram has recently introduced a reel button on home page.[]

On June 17, , Instagram launched full-screen advertisements in Reels. The ads are similar to regular reels and can run up to 30 seconds. They are distinguished from regular content by the "sponsored" tag under the account name.[]

Instagram Direct

In December , Instagram announced Instagram Direct, a feature that lets users interact through private messaging. Users who follow each other can send private messages with photos and videos, in contrast to the public-only requirement that was previously in place. When users receive a private message from someone they don't follow, the message is marked as pending and the user must accept to see it. Users can send a photo to a maximum of 15 people.[][][] The feature received a major update in September , adding conversation threading and making it possible for users to share locations, hashtag pages, and profiles through private messages directly from the news feed. Additionally, users can now reply to private messages with text, emoji or by clicking on a heart icon. A camera inside Direct lets users take a photo and send it to the recipient without leaving the conversation.[][][] A new update in November let users make their private messages "disappear" after being viewed by the recipient, with the sender receiving a notification if the recipient takes a screenshot.[][]

In April , Instagram redesigned Direct to combine all private messages, both permanent and ephemeral, into the same message threads.[][][] In May, Instagram made it possible to send website links in messages, and also added support for sending photos in their original portrait or landscape orientation without cropping.[][]

In April , Direct became accessible from the Instagram website, allowing users to send direct messages from a web version using WebSocket technology.[]

In August , Facebook started merging Instagram Direct into Facebook Messenger. After the update (which is rolled out to a segment of the user base) the Instagram Direct icon transforms into Facebook Messenger icon.[]

In March , a feature was added that prevents adults from messaging users under 18 who do not follow them as part of a series of new child safety policies.[][][]

Instagram Stories

In August , Instagram launched Instagram Stories, a feature that allows users to take photos, add effects and layers, and add them to their Instagram story. Images uploaded to a user's story expire after 24 hours. The media noted the feature's similarities to Snapchat.[][] In response to criticism that it copied functionality from Snapchat, CEO Kevin Systrom told Recode that "Day One: Instagram was a combination of Hipstamatic, Twitter [and] some stuff from Facebook like the 'Like' button. You can trace the roots of every feature anyone has in their app, somewhere in the history of technology". Although Systrom acknowledged the criticism as "fair", Recode wrote that "he likened the two social apps' common features to the auto industry: Multiple car companies can coexist, with enough differences among them that they serve different consumer audiences". Systrom further stated that "When we adopted [Stories], we decided that one of the really annoying things about the format is that it just kept going and you couldn't pause it to look at something, you couldn't rewind. We did all that, we implemented that." He also told the publication that Snapchat "didn't have filters, originally. They adopted filters because Instagram had filters and a lot of others were trying to adopt filters as well."[][]

In November, Instagram added live video functionality to Instagram Stories, allowing users to broadcast themselves live, with the video disappearing immediately after ending.[][]

In January , Instagram launched skippable ads, where five-second photo and second video ads appear in-between different stories.[][][]

In April , Instagram Stories incorporated augmented reality stickers, a "clone" of Snapchat's functionality.[][][]

In May , Instagram expanded the augmented reality sticker feature to support face filters, letting users add specific visual features onto their faces.[][]

Later in May, TechCrunch reported about tests of a Location Stories feature in Instagram Stories, where public Stories content at a certain location are compiled and displayed on a business, landmark or place's Instagram page.[] A few days later, Instagram announced "Story Search", in which users can search for geographic locations or hashtags and the app displays relevant public Stories content featuring the search term.[][]

In June , Instagram revised its live-video functionality to allow users to add their live broadcast to their story for availability in the next 24 hours, or discard the broadcast immediately.[] In July, Instagram started allowing users to respond to Stories content by sending photos and videos, complete with Instagram effects such as filters, stickers, and hashtags.[][]

Stories were made available for viewing on Instagram's mobile and desktop websites in late August [][]

On December 5, , Instagram introduced "Story Highlights",[] also known as "Permanent Stories", which are similar to Instagram Stories, but don't expire. They appear as circles below the profile picture and biography and are accessible from the desktop website as well.

In June , the daily active story users of Instagram had reached &#;million users, and monthly active users had reached 1&#;billion active users.[]

Advertising

Emily White joined Instagram as Director of Business Operations in April [][] She stated in an interview with The Wall Street Journal in September that the company should be ready to begin selling advertising by September as a way to generate business from a popular entity that had not yet created profit for its parent company.[] White left Instagram in December to join Snapchat.[][] In August , James Quarles became Instagram's Global Head of Business and Brand Development, tasked with overseeing advertisement, sales efforts, and developing new "monetization products", according to a spokesperson.[]

In October , Instagram announced that video and image ads would soon appear in feeds for users in the United States,[][] with the first image advertisements displaying on November 1, [][] Video ads followed nearly a year later on October 30, [][] In June , Instagram announced the rollout of ads in the United Kingdom, Canada and Australia,[] with ads starting to roll out that autumn.[]

In March , Instagram announced it would implement "carousel ads," allowing advertisers to display multiple images with options for linking to additional content.[][] The company launched carousel image ads in October ,[][] and video carousel ads in March []

In May , Instagram launched new tools for business accounts, including business profiles, analytics and the ability to promote posts as ads. To access the tools, businesses had to link a corresponding Facebook page.[] The new analytics page, known as Instagram Insights, allowed business accounts to view top posts, reach, impressions, engagement and demographic data.[] Insights rolled out first in the United States, Australia, and New Zealand, and expanded to the rest of the world later in [][][]

In February , Instagram announced that it had ,&#;advertisers on the platform.[] This number increased to , by September ,[] and 1&#;million in March [][]

In November , Instagram added the ability for business accounts to add product links directing users to a purchase page or to save them to a "shopping list."[] In April , Instagram added the option to "Checkout on Instagram," which allows merchants to sell products directly through the Instagram app.[]

In March , via a blog post, Instagram announced that they are making major moderation changes in order to decrease the flow of disinformation, hoaxes and fake news regarding COVID on its platform, "We'll remove COVID accounts from account recommendations, and we are working to remove some COVID related content from Explore unless posted by a credible health organization. We will also start to downrank content in feed and Stories that has been rated false by third-party fact-checkers."[]

In June , Instagram launched a native affiliate marketing tool creators can use to earn commissions based on sales. Commission-enabled posts are labeled "Eligible for Commission" on the user side to identify them as affiliate posts. Launch partners included Sephora, MAC, and Kopari.[]

Stand-alone apps

Instagram has developed and released three stand-alone apps with specialized functionality. In July , it released Bolt, a messaging app where users click on a friend's profile photo to quickly send an image, with the content disappearing after being seen.[][] It was followed by the release of Hyperlapse in August, an iOS-exclusive app that uses "clever algorithm processing" to create tracking shots and fast time-lapse videos.[][] Microsoft launched a Hyperlapse app for Android and Windows in May , but there has been no official Hyperlapse app from Instagram for either of these platforms to date.[] In October , it released Boomerang, a video app that combines photos into short, one-second videos that play back-and-forth in a loop.[][]

Third-party services

The popularity of Instagram has led to a variety of third-party services designed to integrate with it, including services for creating content to post on the service and generating content from Instagram photos (including physical print-outs), analytics, and alternative clients for platforms with insufficient or no official support from Instagram (such as in the past, iPads).[][]

In November , Instagram announced that effective June 1, , it would end "feed" API access to its platform in order to "maintain control for the community and provide a clear roadmap for developers" and "set up a more sustainable environment built around authentic experiences on the platform", including those oriented towards content creation, publishers, and advertisers. Additionally, third-party clients have been prohibited from using the text strings "insta" or "gram" in their name.[] It was reported that these changes were primarily intended to discourage third-party clients replicating the entire Instagram experience (due to increasing monetization of the service), and security reasons (such as preventing abuse by automated click farms, and the hijacking of accounts). In the wake of the Cambridge Analytica scandal, Instagram began to impose further restrictions on its API in [][][]

For unlimited browsing of public Instagram profiles without having to create an account, as well as for anonymous browsing of someone else's Stories, has to use the Instagram profiles viewer.[] Stories are more authentic than typical photos posted as posts because users know that in 24 hours their Stories will disappear if they don't add them as highlighted[] (however users can check who saw their Story for 48 hours after it was published[]). For this reason, they are very valuable for market research.[]

Fact checking

On December 16, , Facebook announced it would expand its fact checking programs towards Instagram,[] by using third-party fact-checkers organizations false information is able to be identified, reviewed and labeled as false information. Content when rated as false or partly false is removed from the explore page and hashtag pages, additionally content rated as false or partly false are labeled as such. With the addition of Facebook fact-checking program came the use of image matching technology to find further instances of misinformation. If a piece of content is labeled false or partly false on Facebook or Instagram then duplicates of such content will also be labeled as false.[]

Algorithm and design changes

In April , Instagram began rolling out a change to the order of photos visible in a user's timeline, shifting from a strictly chronological order to one determined by an algorithm.[] Instagram said the algorithm was designed so that users would see more of the photos by users that they liked,[] but there was significant negative feedback, with many users asking their followers to turn on post notifications in order to make sure they see updates.[][][] The company wrote a tweet to users upset at the prospect of the change, but did not back down,[] nor provide a way to change it back, which they re-affirmed in [][]

Since , Instagram has employed the ability to reduce the prominence of accounts ("shadowbanning") it believes may be generating non-genuine engagement and spam (including excessive use of unneeded hashtags), preventing posts from appearing in search results and in the app's Explore section. In a now-deleted Facebook post, Instagram wrote that "When developing content, we recommend focusing on your business objective or goal rather than hashtags".[][] Instagram has since been accused of extending the practice to censor posts under vague and inconsistent circumstances, particularly in regards to sexually suggestive material.[]

Instagram caused the userbase to fall into outrage with the December update.[][][][][] They found an attempt to alter the flow of the feed from the traditional vertical scroll to emulate and piggy-back the popularity of their Instagram Stories with a horizontal scroll, by swiping left.[] Various backtracking statements were released explaining it as a bug, or as a test release that had been accidentally deployed to too large an audience.[][]

In November , Instagram replaced the activity feed tab with a new "Shop" tab, moving the activity feed to the top. The "new post" button was also relocated to the top and replaced with a Reels tab[] The company states that "the Shop tab gives you a better way to connect with brands and creators and discover products you love" and the Reels tab "makes it easier for you to discover short, fun videos from creators all over the world and people just like you."[] However, users have not responded well to the change, taking their complaints to Twitter and Reddit, and The New York Times has shunned Reels in particular, saying "Not only does Reels fail in every way as a TikTok clone, but it’s confusing, frustrating and impossible to navigate".[]

Also in , Instagram rolled out a feature titled "suggested posts", which adds posts from accounts Instagram thinks a user would like to such user's feed.[] The feature was met with controversy from both Reddit users[] from The Verge, which reported that suggested posts would keep users glued to their feed, give Instagram more advertising space, and ultimately harm the mental health of users, while Instagram executive Julian Gutman rebutted, stating the feature was not intended to keep users glued to their screens.[] Suggested posts received more controversy after Fast Company stated that the feature would be impossible to turn off.[]

On 23 June , Instagram announced a test change to the "suggested posts" feature. The company will put suggested posts ahead of posts from people that the user is following in the Instagram feed, citing positive reception as the reason for this change.[]

Impact on people

Mental health

Depression

Khodarahimi & Fathi found evidence for Instagram users displaying higher levels of depressive symptoms.[] Frison & Eggermont pointed out that only Instagram browsing, and not Instagram liking nor posting, predicts more depressive symptoms.[] It also provides evidence for a relation between Instagram use and depressive symptomatology in the opposite direction, where level of depressed mood has shown to positively predict Instagram posting. Lamp et al showed a positive relationship between depression and the number of selfies taken before posting it on Instagram.[]

Anxiety

Khodarahimi & Fathi observed higher levels of anxiety in Instagram users compared to non-users,[] while Mackson et al suggested beneficial effects of Instagram use on anxiety symptoms.[] Multiple studies pointed out small to moderate positive relationships between time spent on Instagram and trait anxiety, physical appearance anxiety, social anxiety and attention to high insecurity-eliciting body regions.[][][][]

Stress

A paper showed that users who feel that they spend too much time on Instagram report higher levels of Instagram addiction, which in turn was related to higher self-reported levels of Instagram induced stress.[][]

Addiction

In a study focusing on the relationship between various psychological needs and Instagram addiction by students, Foroughi et al found that the desire for recognition and entertainment were predictors of students' addition to Instagram. In addition, the study proved that Instagram addiction negatively affect academic performance.[] Gezgin & Mihci quantified Turkish student's Instagram use's contribution to overall smartphone addiction, and concluded that frequent instagraming correlates with addiction to smartphone.[]

Satisfaction with appearance

Sherlock & Wagstaff showed that both the number of followers and followees show a small positive relationship with trait anxiety.[] Instagram users report higher body surveillance,[] appearance related pressure,[] eating pathology[] and lower body satisfaction[] than non-users.[] Multiple studies have shown that users who take more selfies (before posting) and strategically present themselves on Instagram, for example by editing or manipulating selfies, report higher levels of body surveillance, body dissatisfaction, and lower body esteem.[][][][] Tiggemann et al also confirmed this through experimental study, finding that taking and editing selfies led to higher facial dissatisfaction.[][]

False self-presentation

In a study Mun & Kim pointed out that Instagram users with a strong need for approval were more likely to create false presentation of themselves on their Instagram accounts, which in turn increased the likelihood of depression. Notably, depression was mitigated by the perception of popularity.[]

Body image

Multiple studies confirmed that Instagram usage is associated with body surveillance and body self-image. In particular, following appearance-focused Instagrammers corresponded with the desire to look thin. Comments related to appearance on Instagram are leading to higher dissatisfactions with one’s body.[][][][] Based on Facebook's leaked internal research, Instagram has negative effects on the body image of one in three teenagers.[] Leaked internal documents also indicate that two thirds of teen girls and 40 percent of teen boys experience negative social comparison, and that Instagram makes 20 percent of the teens feel worse about themselves. According to the leaked research, Instagram has higher impact on appearance comparison than TikTok or Snapchat.[]

Loneliness

Mackson et al found that Instagram users were less lonely than non-users [] and that Instagram membership predicts lower self-reported loneliness.[]

Social exclusion

In a study by Büttnera et Rudertb[] pointed out that not being tagged in an Instagram photo triggers the feeling of social exclusion and ostracism, especially for those with higher needs to belong.

Wellbeing

The relationship between Instagram usage intensity and wellbeing varies by wellbeing indicator. Brailovskaia & Margraf found a significant positive relationship between Instagram membership and extraversion, life satisfaction, and social support. The association between Instagram membership and conscientiousness was marginally significantly negative. The same study showed a positive relationship between extraversion, life satisfaction, social support and Instagram membership.[]

Life satisfaction

Fioravanti et al showed that women who had to take a break from Instagram for seven days reported higher life satisfaction compared to women who continued their habitual pattern of Instagram use. The effects seemed to be specific for women, where no significant differences were observed for men.[]

Alcohol and drug use

Instagram usage intensity shows a small positive correlation with alcohol consumption, with binge drinkers reporting greater intensity of Instagram use than non-binge drinkers.[] An earlier study examined the relationship between alcohol consumption during college. It found a small to moderate positive relationship between alcohol consumption and Instagram usage, enhanced drinking motives, and drinking behavior.[]

Fear of Missing Out

The relationship between Instagram use and the fear of missing out (FoMo) has been confirmed in multiple studies.[][] Use intensity shows a strong, while the number of followers and followees shows a weak correlation with FoMo. Research shows that Instagram browsing predicts social comparison, which generates FoMo, and FoMo can ultimately lead to depression.[]

Eating disorders

A comparison of Instagram users with non-users showed that boys with an Instagram account differ from boys without an account in terms of over-evaluation of their shape and weight, skipping meals, and levels of reported disordered eating cognitions. Girls with an Instagram account also differed from girls without an account in terms of skipping meals. However, none of the other associations that were reported for boys were observed for girls. Instead, girls with an Instagram account differed from girls without an account in that they used a stricter exercise schedule. This suggests a possible differential effect of Instagram membership on body (dis)satisfaction and disordered eating for boys and girls.[][] Regarding the relationship between time spent on Instagram and body image and/or disordered eating, several body-related constructs were consistently linked to indicators of Instagram use. More specifically, several studies identified a small positive relationship between time spent on Instagram and both internalization of beauty ideals or muscular ideals, and self-objectification across studies.[][][][] A positive link has been pointed out between the intensity of Instagram use and both body surveillance and dietary behaviors or disordered eating.[][]

Suicide and self-harm

Picardo et al examined the relationship between self-harm posts and actual self-harm behaviours offline and found such content had negative emotional effects on some users and reported preliminary evidence of potential harmful effects in relation to self-harm related behaviours offline, although causal effects cannot be claimed. At the same time, some benefits for those who engage with self-harm content online have been suggested.[] Instagram has published content to help users in need to get support.[]

Based on Facebook's leaked internal research, 13 percent of British teenager users with suicidal thoughts could trace these thoughts to Instagram use. Amongst teenagers in the US with suicidal thoughts, this number is much smaller - 6 percent.[]

Impact on businesses

Instagram can help promote commercial products and services. It can be distinguished from other social media platforms by its focus on visual communication. Instagram marketing is an effective way to advertise a product, given that a picture is said to speak a thousand words.[] The platform can also help commercial entities save branding costs, as it can be used for free even for commercial purposes.

User characteristics and behavior

The Instagram app, running on the Androidoperating system

Users

See also: List of most-followed Instagram accounts

Following the release in October, Instagram had one million registered users in December [][] In June , it announced that it had 5&#;million users,[] which increased to 10&#;million in September.[][] This growth continued to 30&#;million users in April ,[][30] 80&#;million in July ,[][] &#;million in February ,[][] &#;million in June ,[] &#;million in September ,[][] &#;million in December ,[][] &#;million in September ,[][] &#;million in June ,[][] &#;million in December ,[][] &#;million in April ,[][] and &#;million in September [][]

In October , Instagram Stories reached &#;million active users, two months after launch.[][] This increased to &#;million in January ,[][] &#;million in April, surpassing Snapchat's user growth,[][][] and &#;million active users in June [][]

In April , Instagram Direct had &#;million monthly users.[][][]

In June , Instagram passed &#;million photos uploaded to the service.[][] This grew to &#;million in August ,[][] and by June , there were over 16&#;billion photos on the service.[] In October , there existed over 40&#;billion photos.[]

Demographics

As of [update], Instagram's users are divided equally with 50% iPhone owners and 50% Android owners. While Instagram has a neutral gender-bias format, 68% of Instagram users are female while 32% are male. Instagram's geographical use is shown to favor urban areas as 17% of US adults who live in urban areas use Instagram while only 11% of adults in suburban and rural areas do so. While Instagram may appear to be one of the most widely used sites for photo sharing, only 7% of daily photo uploads, among the top four photo-sharing platforms, come from Instagram. Instagram has been proven to attract the younger generation with 90% of the &#;million users under the age of From June to June , Instagram approximately doubled their number of users. With regards to income, 15% of US Internet users who make less than $30, per year use Instagram, while 14% of those making $30, to $50,, and 12% of users who make more than $50, per year do so.[] With respect to the education demographic, respondents with some college education proved to be the most active on Instagram with 23%. Following behind, college graduates consist of 18% and users with a high school diploma or less make up 15%. Among these Instagram users, 24% say they use the app several times a day.[]

User behavior

Ongoing research continues to explore how media content on the platform affects user engagement. Past research has found that media which show peoples' faces receive more 'likes' and comments and that using filters that increase warmth, exposure, and contrast also boosts engagement.[] Users are more likely to engage with images that depict fewer individuals compared to groups and also are more likely to engage with content that has not been watermarked, as they view this content as less original and reliable compared to user-generated content.[] Recently Instagram has come up with an option for users to apply for a verified account badge; however, this does not guarantee every user who applies will get the verified blue tick.[]

The motives for using Instagram among young people are mainly to look at posts, particularly for the sake of social interactions and recreation. In contrast, the level of agreement expressed in creating Instagram posts was lower, which demonstrates that Instagram's emphasis on visual communication is widely accepted by young people in social communication.[]

Reception

In , Washington Post reported that it has made an international black market for migrant workers, women in Africa and Asia, sold into servitude as maids in Persian Gulf countries.[]

Awards

Instagram was the runner-up for "Best Mobile App" at the TechCrunch Crunchies in January [] In May , Fast Company listed CEO Kevin Systrom at number 66 in "The Most Creative People in Business in ".[] In June , Inc. included co-founders Systrom and Krieger in its "30 Under 30" list.[15]

Instagram won "Best Locally Made App" in the SF Weekly Web Awards in September []7x7Magazine's September issue featured Systrom and Krieger on the cover of their "The Hot 20 " issue.[] In December , Apple Inc. named Instagram the "App of the Year" for [] In , Instagram was named No. 1 by Mashable on its list of "The best iPhone apps of all time," noting Instagram as "one of the most influential social networks in the world."[] Instagram was listed among Time's "50 Best Android Applications for " list.[]

Mental health

See also: Social media and suicide

In May , a survey conducted by the United Kingdom's Royal Society for Public Health, featuring 1, people aged 14–24, asking them to rate social media platforms depending on anxiety, depression, loneliness, bullying and body image, concluded that Instagram was the "worst for young mental health". Some have suggested it may contribute to digital dependence, whist this same survey noticed its positive effects, including self-expression, self-identity, and community building. In response to the survey, Instagram stated that "Keeping Instagram a safe and supportive place for young people was a top priority".[][] The company filters out the reviews and accounts. If some of the accounts violate Instagram's community guidelines, it will take action, which could include banning them.[]

In , researchers from Harvard University and University of Vermont demonstrated a machine learning tool that successfully outperformed general practitioners' diagnostic success rate for depression. The tool used color analysis, metadata components, and face detection of users' feeds.[]

Throughout , Instagram began to test the hiding of like counts for posts made by its users.

Correlations have been made between Instagram content and poor body dissatisfaction, as a result of body comparisons. In a recent survey half of the applicants admitted to photo editing behavior which has been linked with concerns over body image.[]

In October , CNN published an article and interviews on how two young women, Ashlee Thomas and Anastasia Vlasova, say Instagram endangered their lives by Instagram having toxic effects on their diets.[]

In response to abusive and negative comments on users' photos, Instagram has made efforts to give users more control over their posts and accompanying comments field. In July , it announced that users would be able to turn off comments for their posts, as well as control the language used in comments by inputting words they consider offensive, which will ban applicable comments from showing up.[][] After the July announcement, the ability to ban specific words began rolling out early August to celebrities,[] followed by regular users in September.[] In December, the company began rolling out the abilities for users to turn off the comments and, for private accounts, remove followers.[][]

In September , the company announced that public users would be able to limit who can comment on their content, such as only their followers or people they follow. At the same time, it updated its automated comment filter to support additional languages.[][]

In June , Instagram announced that it would automatically attempt to filter offensive, harassing, and "spammy" comments by default. The system is built using a Facebook-developed deep learning algorithm known as DeepText (first implemented on the social network to detect spam comments), which utilizes natural-language processing techniques, and can also filter by user-specified keywords.[][][]

In July , the service announced that it would introduce a system to proactively detect problematic comments and encourage the user to reconsider their comment, as well as allowing users the ability to "restrict" others' abilities to communicate with them, citing that younger users felt the existing block system was too much of an escalation.[88]

Culture

On August 9, , English musician Ellie Goulding released a new music video for her song "Anything Could Happen." The video only contained fan-submitted Instagram photographs that used various filters to represent words or lyrics from the song, and over 1, different photographs were submitted.[]

Security

In August , reports surfaced that a bug in Instagram's developer tools had allowed "one or more individuals" to gain access to the contact information, specifically email addresses and phone numbers, of several high-profile verified accounts, including its most followed user, Selena Gomez. The company said in a statement that it had "fixed the bug swiftly" and was running an investigation.[][] However, the following month, more details emerged, with a group of hackers selling contact information online, with the affected number of accounts in the "millions" rather than the previously-assumed limitation on verified accounts. Hours after the hack, a searchable database was posted online, charging $10 per search.[]The Daily Beast was provided with a sample of the affected accounts, and could confirm that, while many of the email addresses could be found with a Google search in public sources, some did not return relevant Google search results and thus were from private sources.[]The Verge wrote that cybersecurity firm RepKnight had found contact information for multiple actors, musicians, and athletes,[] and singer Selena Gomez's account was used by the hackers to post naked photos of her ex-boyfriend Justin Bieber. The company admitted that "we cannot determine which specific accounts may have been impacted", but believed that "it was a low percentage of Instagram accounts", though TechCrunch stated in its report that six million accounts were affected by the hack, and that "Instagram services more than million accounts; six million is not a small number".[]

In , Apple pulled an app that let users stalk people on Instagram by scraping accounts and collecting data.[]

Iran has DPI blocking for Instagram.[]

Content ownership

On December 17, , Instagram announced a change to its Terms of Service policy, adding the following sentence:[]

To help us deliver interesting paid or sponsored content or promotions, you agree that a business or other entity may pay us to display your username, likeness, photos (along with any associated metadata), and/or actions you take, in connection with paid or sponsored content or promotions, without any compensation to you.

There was no option for users to opt out of the changed Terms of Service without deleting their accounts before the new policy went into effect on January 16, [] The move garnered severe criticism from users,[][] prompting Instagram CEO Kevin Systrom to write a blog post one day later, announcing that they would "remove" the offending language from the policy. Citing misinterpretations about its intention to "communicate that we'd like to experiment with innovative advertising that feels appropriate on Instagram", Systrom also stated that it was "our mistake that this language is confusing" and that "it is not our intention to sell your photos". Furthermore, he wrote that they would work on "updated language in the terms to make sure this is clear".[][]

The policy change and its backlash caused competing photo services to use the opportunity to "try to lure users away" by promoting their privacy-friendly services,[] and some services experienced substantial gains in momentum and user growth following the news.[] On December 20, Instagram announced that the advertising section of the policy would be reverted to its original October version.[]The Verge wrote about that policy as well, however, noting that the original policy gives the company right to "place such advertising and promotions on the Instagram Services or on, about, or in conjunction with your Content", meaning that "Instagram has always had the right to use your photos in ads, almost any way it wants. We could have had the exact same freakout last week, or a year ago, or the day Instagram launched".[]

The policy update also introduced an arbitration clause, which remained even after the language pertaining to advertising and user content had been modified.[]

Facebook acquisition as a violation of US antitrust law

Columbia Law School professor Tim Wu has given public talks explaining that Facebook's purchase of Instagram was a felony.[] A New York Post article published on February 26, , reported that "the FTC had uncovered [a document] by a high-ranking Facebook executive who said the reason the company was buying Instagram was to eliminate a potential competitor".[] As Wu explains, this is a violation of US antitrust law (see monopoly). Wu stated that this document was an email directly from Mark Zuckerberg, whereas the Post article had stated that their source had declined to say whether the high-ranking executive was the CEO. The article reported that the FTC "has formed a task force to review "anticompetitive conduct" in the tech world amid concerns that tech companies are growing too powerful. The task force will look at "the full panoply of remedies" if it finds "competitive harm," FTC competition bureau director Bruce Hoffman told reporters."

Algorithmic advertisement with a rape threat

In , Olivia Solon, a reporter for The Guardian, posted a screenshot to her Instagram profile of an email she had received containing threats of rape and murder towards her. The photo post had received three likes and countless comments, and in September , the company's algorithms turned the photo into an advertisement visible to Solon's sister. An Instagram spokesperson apologized and told The Guardian that "We are sorry this happened – it's not the experience we want someone to have. This notification post was surfaced as part of an effort to encourage engagement on Instagram. Posts are generally received by a small percentage of a person's Facebook friends." As noted by the technology media, the incident occurred at the same time parent company Facebook was under scrutiny for its algorithms and advertising campaigns being used for offensive and negative purposes.[][]

Censorship and restricted content

According to a Facebook spokesperson, on January 11, , Instagram and its parent company Facebook, Inc. are removing posts "that voice support for slain Iranian commander Qassem Soleimani to comply with US sanctions".[]

Illicit drugs

Instagram has been the subject of criticism due to users publishing images of drugs they are selling on the platform. In , the BBC discovered that users, mostly located in the United States, were posting images of drugs they were selling, attaching specific hashtags, and then completing transactions via instant messaging applications such as WhatsApp. Corresponding hashtags have been blocked as part of the company's response and a spokesperson engaged with the BBC explained:[][]

Instagram has a clear set of rules about what is and isn't allowed on the site. We encourage people who come across illegal or inappropriate content to report it to us using the built-in reporting tools next to every photo, video or comment, so we can take action. People can't buy things on Instagram, we are simply a place where people share photos and videos.

However, new incidents of illegal drug trade have occurred in the aftermath of the revelation, with Facebook, Inc., Instagram's parent company, asking users who come across such content to report the material, at which time a "dedicated team" reviews the information.[]

In , Facebook announced that influencers are no longer able to post any vape, tobacco products, and weapons promotions on Facebook and Instagram.[]

Women's bodies

In October , Instagram deleted the account of Canadian photographer Petra Collins after she posted a photo of herself in which a very small area of pubic hair was visible above the top of her bikini bottom. Collins claimed that the account deletion was unfounded because it broke none of Instagram's terms and conditions.[] Audra Schroeder of The Daily Dot further wrote that "Instagram's terms of use state users can't post "pornographic or sexually suggestive photos," but who actually gets to decide that? You can indeed find more sexually suggestive photos on the site than Collins', where women show the side of "femininity" the world is "used to" seeing and accepting."[] Nick Drewe of The Daily Beast wrote a report the same month focusing on hashtags that users are unable to search for, including #sex, #bubblebutt, and #ballsack, despite allowing #faketits, #gunsforsale and #sexytimes, calling the discrepancy "nonsensical and inconsistent".[]

Similar incidents occurred in January , when Instagram deleted Australian fashion agency Sticks and Stones Agency's account because of a photograph including pubic hair sticking out of bikini bottoms,[] and March , when artist and poet Rupi Kaur's photos of menstrual blood on clothing were removed, prompting a rallying post on her Facebook and Tumblr accounts with the text "We will not be censored", gaining over 11, shares.[]

The incidents have led to a #FreetheNipple campaign, aimed at challenging Instagram's removal of photos displaying women's nipples. Although Instagram has not made many comments on the campaign,[] an October explanation from CEO Kevin Systrom highlighted Apple's content guidelines for apps published through its App Store, including Instagram, in which apps must designate the appropriate age ranking for users, with the app's current rating being 12+ years of age. However, this statement has also been called into question due to other apps with more explicit content allowed on the store, the lack of consequences for men exposing their bodies on Instagram, and for inconsistent treatment of what constitutes inappropriate exposure of the female body.[][]

Censorship by countries

Instagram is the most popular social networking site in Iran(in red), also the only country where this is the case.

Censorship of Instagram has occurred in several different countries.

United States

On October 30, , Instagram temporarily removed the "recent" tab on hashtag pages to prevent the spread of misinformation regarding the United States presidential election.[] On January 7, , United States PresidentDonald Trump was banned from Instagram "indefinitely". Zuckerberg stated "We believe the risks of allowing the President to continue to use our service during this period are simply too great."[]

China

See also: Internet censorship in China

Instagram has been blocked by China following the Hong Kong protests as many confrontations with police and incidents occurring during the protests were recorded and photographed. Hong Kong and Macau were not affected as they are part of special administrative regions of China.[]

Turkey

Turkey is also known for its strict Internet censorship and periodically blocks social media including Instagram.[]

North Korea

See also: Internet in North Korea

A few days after a fire incident that happened in the Koryo Hotel in North Korea on June 11, , authorities began to block Instagram to prevent photos of the incident from being spread out.[]

Iran

Iran has sentenced several citizens to prison for posts made on their Instagram accounts.[] The Iranian government also blocked Instagram periodically during anti-government protests.[] In July , Instagram temporarily censored videos with the phrase "death to Khamenei".[]

Cuba

The Cuban government blocked access to several social media platforms, including Instagram, to curb the spread of information during the Cuban protests.[]

In popular culture

System

Instagram is written in Python.[]

Instagram AI describes content for visually impaired people that use screen readers.[]

See also

Notes

  1. ^The name is often colloquially abbreviated as IG, Insta, or the Gram.[9]

References

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  43. ^ ab
Источник: [shoppingdowntown.us]

Polystyrene

Polymer

For other uses, see Polystyrene (disambiguation).

Repeating unit of PS polymer chain
Polystyrene-chain-from-xtal-3D-bspng
shoppingdowntown.us
Names
IUPAC name

Poly(1-phenylethene)

Other names

Thermocol

Identifiers

CAS Number

Abbreviations PS
ChemSpider
ECHA InfoCardEdit this at Wikidata

CompTox Dashboard(EPA)

Properties

Chemical formula

(C8H8)n
Density–&#;g/cm3
Melting point~&#;&#;°C (&#;°F; &#;K)[4] For Isotactic Polystyrene
Boiling point &#;°C (&#;°F; &#;K) and depolymerizes

Solubility in water

Insoluble
SolubilitySoluble in benzene, carbon disulfide, chlorinated aliphatic hydrocarbons, chloroform, cyclohexanone, dioxane, ethyl acetate, ethylbenzene, MEK, NMP, THF [1]
Thermal conductivity W/(m·K) (foam, ρ g/cm3)[2]

Refractive index (nD)

; dielectric constant (1 kHz – 1 GHz)
Related compounds

Related compounds

Styrene (monomer)

Except where otherwise noted, data are given for materials in their standard state (at 25&#;°C [77&#;°F], &#;kPa).

Infobox&#;references

Chemical compound

Expanded polystyrene packaging
A polystyrene yogurt container

Polystyrene (PS) is a synthetic aromatichydrocarbonpolymer made from the monomer known as styrene.[5] Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a poor barrier to oxygen and water vapour and has a relatively low melting point.[6] Polystyrene is one of the most widely used plastics, the scale of its production being several million tonnes per year.[7] Polystyrene can be naturally transparent, but can be coloured with colourants. Uses include protective packaging (such as packing peanuts and in the jewel cases used for storage of optical discs such as CDs and occasionally DVDs), containers, lids, bottles, trays, tumblers, disposablecutlery,[6] in the making of models, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, and as an alternative material for phonograph records.[8]

As a thermoplastic polymer, polystyrene is in a solid (glassy) state at room temperature but flows if heated above about &#;°C, its glass transition temperature. It becomes rigid again when cooled. This temperature behaviour is exploited for extrusion (as in Styrofoam) and also for molding and vacuum forming, since it can be cast into molds with fine detail.

Under ASTM standards, polystyrene is regarded as not biodegradable. It is accumulating as a form of litter in the outside environment, particularly along shores and waterways, especially in its foam form, and in the Pacific Ocean.[9]

History[edit]

Polystyrene was discovered in by Eduard Simon, an apothecary from Berlin.[10] From storax, the resin of the Oriental sweetgum tree Liquidambar orientalis, he distilled an oily substance, a monomer that he named styrol. Several days later, Simon found that the styrol had thickened into a jelly he dubbed styrol oxide ("Styroloxyd") because he presumed an oxidation. By Jamaican-born chemist John Buddle Blyth and German chemist August Wilhelm von Hofmann showed that the same transformation of styrol took place in the absence of oxygen.[11] They called the product "meta styrol"; analysis showed that it was chemically identical to Simon's Styroloxyd.[12] In Marcellin Berthelot correctly identified the formation of meta styrol/Styroloxyd from styrol as a polymerisation process.[13] About 80 years later it was realized that heating of styrol starts a chain reaction that produces macromolecules, following the thesis of German organic chemist Hermann Staudinger (–). This eventually led to the substance receiving its present name, polystyrene.[citation needed]

The company I. G. Farben began manufacturing polystyrene in Ludwigshafen, abouthoping it would be a suitable replacement for die-cast zinc in many applications. Success was achieved when they developed a reactor vessel that extruded polystyrene through a heated tube and cutter, producing polystyrene in pellet form.[citation needed]

Otis Ray McIntire () a chemical engineer of Dow Chemical rediscovered a process first patented by Swedish inventor Carl Munters.[14] According to the Science History Institute, "Dow bought the rights to Munters’s method and began producing a lightweight, water-resistant, and buoyant material that seemed perfectly suited for building docks and watercraft and for insulating homes, offices, and chicken sheds."[15] InStyrofoam was patented.[citation needed]

Beforechemical engineer Fritz Stastny (–) developed pre-expanded PS beads by incorporating aliphatic hydrocarbons, such as pentane. These beads are the raw material for molding parts or extruding sheets. BASF and Stastny applied for a patent that was issued in The molding process was demonstrated at the Kunststoff Messe in Düsseldorf. Products were named Styropor.[citation needed]

The crystal structure of isotactic polystyrene was reported by Giulio Natta.[16]

Inthe Koppers Company in Pittsburgh, Pennsylvania, developed expanded polystyrene (EPS) foam under the trade name Dylite.[17] InDart Container, the largest manufacturer of foam cups, shipped their first order.[18]

Structure[edit]

In chemical terms, polystyrene is a long chain hydrocarbon wherein alternating carbon centers are attached to phenyl groups (a derivative of benzene). Polystyrene's chemical formula is (C
8H
8)
n; it contains the chemical elementscarbon and hydrogen.[citation needed]

The material's properties are determined by short-range van der Waals attractions between polymers chains. Since the molecules consist of thousands of atoms, the cumulative attractive force between the molecules is large. When heated (or deformed at a rapid rate, due to a combination of viscoelastic and thermal insulation properties), the chains can take on a higher degree of confirmation and slide past each other. This intermolecular weakness (versus the high intramolecular strength due to the hydrocarbon backbone) confers flexibility and elasticity. The ability of the system to be readily deformed above its glass transition temperature allows polystyrene (and thermoplastic polymers in general) to be readily softened and molded upon heating. Extruded polystyrene is about as strong as an unalloyed aluminium but much more flexible and much less dense ( g/cm3 for polystyrene vs. g/cm3 for aluminium).[citation needed]

Production[edit]

Polystyrene is an addition polymer that results when styrene monomers interconnect (polymerization). In the polymerization, the carbon-carbon π bond of the vinyl group is broken and a new carbon-carbon σ bond is formed, attaching to the carbon of another styrene monomer to the chain. Since only one kind of monomer is used in its preparation, it is a homopolymer. The newly formed σ bond is stronger than the π bond that was broken, thus it is difficult to depolymerize polystyrene. About a few thousand monomers typically comprise a chain of polystyrene, giving a molecular weight of ,–, g/mol.[citation needed]

Polystyrene shoppingdowntown.us

Each carbon of the backbone has tetrahedral geometry, and those carbons that have a phenyl group (benzene ring) attached are stereogenic. If the backbone were to be laid as a flat elongated zig-zag chain, each phenyl group would be tilted forward or backward compared to the plane of the chain.[citation needed]

The relative stereochemical relationship of consecutive phenyl groups determines the tacticity, which affects various physical properties of the material.[citation needed]

Tacticity[edit]

In polystyrene, tacticity describes the extent to which the phenyl group is uniformly aligned (arranged at one side) in the polymer chain. Tacticity has a strong effect on the properties of the plastic. Standard polystyrene is atactic. The diastereomer where all of the phenyl groups are on the same side is called isotactic polystyrene, which is not produced commercially.[citation needed]

Polystyrene tacticity shoppingdowntown.us

Atactic polystyrene[edit]

The only commercially important form of polystyrene is atactic, in which the phenyl groups are randomly distributed on both sides of the polymer chain. This random positioning prevents the chains from aligning with sufficient regularity to achieve any crystallinity. The plastic has a glass transition temperature Tg of ~90&#;°C. Polymerization is initiated with free radicals.[7]

Syndiotactic polystyrene[edit]

Ziegler–Natta polymerization can produce an ordered syndiotactic polystyrene with the phenyl groups positioned on alternating sides of the hydrocarbon backbone. This form is highly crystalline with a Tm (melting point) of &#;°C (&#;°F). Syndiotactic polystyrene resin is currently produced under the trade name XAREC by Idemitsu corporation, who use a metallocene catalyst for the polymerisation reaction.[19]

Degradation[edit]

Polystyrene is relatively chemically inert. While it is waterproof and resistant to breakdown by many acids and bases, it is easily attacked by many organic solvents (e.g. it dissolves quickly when exposed to acetone), chlorinated solvents, and aromatic hydrocarbon solvents. Because of its resilience and inertness, it is used for fabricating many objects of commerce. Like other organic compounds, polystyrene burns to give carbon dioxide and water vapor, in addition to other thermal degradation by-products. Polystyrene, being an aromatic hydrocarbon, typically combusts incompletely as indicated by the sooty flame.[citation needed]

The process of depolymerizing polystyrene into its monomer, styrene, is called pyrolysis. This involves using high heat and pressure to break down the chemical bonds between each styrene compound. Pyrolysis usually goes up to &#;°C.[20] The high energy cost of doing this has made commercial recycling of polystyrene back into styrene monomer difficult.[citation needed]

Organisms[edit]

Polystyrene is generally considered to be non-biodegradable. However, certain organisms are able to degrade it, albeit very slowly.[21]

Inresearchers discovered that mealworms, the larvae form of the darkling beetle Tenebrio molitor, could digest and subsist healthily on a diet of EPS.[22][23] About mealworms could consume between 34 and 39 milligrams of this white foam in a day. The droppings of mealworm were found to be safe for use as soil for crops.[22]

Init was also reported that superworms (Zophobas morio) may eat expanded polystyrene (EPS).[24] A group of high school students in Ateneo de Manila University found that compared to Tenebrio molitor larvae, Zophobas morio larvae may consume greater amounts of EPS over longer periods of time.[25]

The bacterium Pseudomonas putida is capable of converting styrene oil into the biodegradable plasticPHA.[26][27][28] This may someday be of use in the effective disposing of polystyrene foam. It is worthy to note the polystyrene must undergo pyrolysis to turn into styrene oil.[citation needed]

Forms produced[edit]

Polystyrene is commonly injection molded, vacuum formed, or extruded, while expanded polystyrene is either extruded or molded in a special process. Polystyrene copolymers are also produced; these contain one or more other monomers in addition to styrene. In recent years the expanded polystyrene composites with cellulose[32][33] and starch[34] have also been produced. Polystyrene is used in some polymer-bonded explosives (PBX).[citation needed]

Sheet or molded polystyrene[edit]

CD case made from general purpose polystyrene (GPPS) and high impact polystyrene (HIPS)
Disposable polystyrene razor

Polystyrene (PS) is used for producing disposable plastic cutlery and dinnerware, CD "jewel" cases, smoke detector housings, license plate frames, plastic model assembly kits, and many other objects where a rigid, economical plastic is desired. Production methods include thermoforming (vacuum forming) and injection molding.

Polystyrene Petri dishes and other laboratory containers such as test tubes and microplates play an important role in biomedical research and science. For these uses, articles are almost always made by injection molding, and often sterilized post-molding, either by irradiation or by treatment with ethylene oxide. Post-mold surface modification, usually with oxygen-rich plasmas, is often done to introduce polar groups, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. Much of modern biomedical Duplicate Image Finder Quick Update v1.0.03 crack serial keygen relies on the use of such products; they, therefore, play a critical role in pharmaceutical research.[35]

Thin sheets of polystyrene are used in polystyrene film capacitors as it forms a very stable dielectric, but has largely fallen out of use in favor of polyester.

Foams[edit]

Closeup of expanded polystyrene packaging

Polystyrene foams are % air.[36][37] Polystyrene foams are good thermal insulators and are therefore often used as building insulation materials, such as in insulating concrete forms and structural insulated panel building systems. Grey polystyrene foam, incorporating graphite, has superior insulation properties.[38]

Carl Munters and John Gudbrand Tandberg of Sweden received a US patent for polystyrene foam as an insulation product in (USA patent number 2,).[39]

PS foams also exhibit good damping properties, therefore it is used widely in packaging. The trademarkStyrofoam by Dow Chemical Company is informally used (mainly US & Canada) for all foamed polystyrene products, although strictly it should only be used for "extruded closed-cell" polystyrene foams made by Dow Chemicals.

Foams are also used for non-weight-bearing architectural structures (such as ornamental pillars).

Expanded polystyrene (EPS)[edit]

Thermocol slabs made of expanded polystyrene (EPS) beads. The one on the left is from a packing box. The one on the right is used for crafts. It has a corky, papery texture and is used for stage decoration, exhibition models, and sometimes as a cheap alternative to shola (Aeschynomene aspera) stems for artwork.
Section of a block of thermocol under a light microscope(bright-field, objective = 10×, eyepiece = 15×). The larger spheres are expanded polystyrene beads which were compressed and fused. The bright, star-shaped hole at the center of the image is an air-gap between the beads where the bead margins have not completely fused. Each bead is made of thin-walled, air-filled bubbles of polystyrene.

Expanded polystyrene (EPS) is a rigid and tough, closed-cell foam with a normal density range of 11 to 32&#;kg/m3.[40] It is usually white and made of pre-expanded polystyrene beads. The manufacturing process for EPS conventionally begins with the creation of small polystyrene beads. Styrene monomers (and potentially other additives) are suspended in water, where they undergo free-radical addition polymerization. The polystyrene beads formed by this mechanism may have an average diameter of around &#;μm. The beads are then permeated with a "blowing agent", a material that enables the beads to be expanded. Pentane is commonly used as the blowing agent. The beads are added to a continuously agitated reactor with the blowing agent, among other additives, and the blowing agent seeps into pores within each bead. The beads are then expanded using steam.[41]

EPS is used for food containers, molded sheets for building insulation, and packing material either as solid blocks formed to accommodate the item being protected or as loose-fill "peanuts"cushioning fragile items inside boxes. EPS also has been widely used in automotive and road safety applications such as motorcycle helmets and road barriers on automobile race tracks.[42][43][44]

A significant portion of all EPS products are manufactured through injection molding. Mold tools tend to be manufactured from steels (which can be hardened and plated), and aluminum alloys. The molds are controlled through a split via a channel system of gates and runners.[45] EPS is colloquially called "styrofoam" in the United States and Canada, an incorrectly applied genericization of Dow Chemical's brand of extruded polystyrene.[46]

EPS in building construction[edit]

Sheets of EPS are commonly packaged as rigid panels (Common in Europe is a size of &#;cm x 50&#;cm, usually depending on an intended type of connection and glue techniques, it is, in fact, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, &#;cm x &#;cm or 98&#;cm x 48&#;cm; less common is x 60&#;cm; size 4 by 8&#;ft ( by &#;m) or 2 by 8&#;ft ( by &#;m) in the United States). Common thicknesses are from 10&#;mm to &#;mm. Many customizations, additives, and thin additional external layers on one or both sides are often added to help with various properties.

Thermal conductivity is measured according to EN Typical values range from to &#;W/(m⋅K) depending on the density of the EPS board. The value of &#;W/(m⋅K) was obtained at 15&#;kg/m3 while the value of &#;W/(m⋅K) was obtained at 40&#;kg/m3 according to the datasheet of K from StyroChem Finland. Adding fillers (graphites, aluminum, or carbons) has recently allowed the thermal conductivity of EPS to reach around –&#;W/(m⋅K) (as low as &#;W/(m⋅K)) and as such has a grey/black Duplicate Image Finder Quick Update v1.0.03 crack serial keygen which distinguishes it from standard EPS. Several EPS producers have produced a variety of these increased thermal resistance EPS usage for this product in the UK and EU.

Water vapor diffusion resistance (μ) of EPS is around 30–

ICC-ES (International Code Council Evaluation Service) requires EPS boards used in building construction meet ASTM C requirements. One of these requirements is that the limiting oxygen index of EPS as measured by ASTM D be greater than 24 volume&#;%. Typical EPS has an oxygen index of around 18 volume&#;%; thus, a flame retardant is added to styrene or polystyrene during the formation of EPS.

The boards containing a flame retardant when tested in a tunnel using test method UL or ASTM E84 will have a flame spread index of less than 25 and a smoke-developed index of less than ICC-ES requires the use of a minute thermal barrier when EPS boards are used inside of a building.

According to the EPS-IA ICF organization, the typical density of EPS used for insulated concrete forms ESET Smart Security 14.2.24.0 License Key Plus Username & Password 2021 polystyrene concrete) is to pounds per cubic foot ( to &#;kg/m3). This is either Type II or Type IX EPS according to ASTM C EPS blocks or boards used in building construction are commonly cut using hot wires.[47]

Extruded polystyrene (XPS)[edit]

Extruded polystyrene foam (XPS) consists of closed cells. It offers improved surface roughness, higher stiffness and reduced thermal conductivity. The density range is about 28–45&#;kg/m3.[citation needed]

Extruded polystyrene material is also used in crafts and model building, in particular architectural models. Because of the extrusion manufacturing process, XPS does not require facers to maintain its thermal or physical property performance, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. Thus, it makes a more uniform substitute for corrugated cardboard. Thermal conductivity varies between and W/(m·K) depending on bearing strength/density and the average value is ~ W/(m·K).

Water vapor diffusion resistance (μ) of XPS is around 80–

Commonly extruded polystyrene foam materials include:

Water absorption of polystyrene foams[edit]

Although it is a closed-cell foam, both expanded and extruded polystyrene are not entirely waterproof or vapor proof.[49] In expanded polystyrene there are interstitial gaps between the expanded closed-cell pellets that form an open network of channels between the bonded pellets, and this network of gaps can become filled with liquid water. If the water freezes into ice, it expands and can cause polystyrene pellets to break off from the foam. Extruded polystyrene is also permeable by water molecules and can not be considered a vapor barrier.[50]

Water-logging commonly occurs over a long period in polystyrene foams that are constantly exposed to high humidity or are continuously immersed in water, such as in hot tub covers, in floating docks, as supplemental flotation under boat seats, and for below-grade exterior building insulation constantly exposed to groundwater.[51] Typically an exterior vapor barrier such as impermeable plastic sheeting or a sprayed-on coating is necessary to prevent saturation.

Oriented polystyrene[edit]

Oriented polystyrene (OPS) Duplicate Image Finder Quick Update v1.0.03 crack serial keygen produced by stretching extruded PS film, improving visibility through the material by reducing haziness and increasing stiffness. This is often used in packaging where the manufacturer would like the consumer to see the enclosed product. Some benefits to OPS are that it is less expensive to produce than other clear plastics such as polypropylene (PP), (PET), and high-impact polystyrene Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, and it is less hazy than HIPS or PP. The main disadvantage of OPS is that it is brittle, and will crack or tear easily.

Co-polymers[edit]

Ordinary (homopolymeric) polystyrene has an excellent property profile about transparency, surface quality and stiffness. Its range of applications is further extended by copolymerization and other modifications (blends e.g. with PC and syndiotactic polystyrene).[52]:&#;–&#; Several copolymers are used based on styrene: The crispiness of homopolymeric polystyrene is overcome by elastomer-modified styrene-butadiene copolymers. Copolymers of styrene and acrylonitrile (SAN) are more resistant to thermal stress, heat and chemicals than homopolymers and are also transparent. Copolymers called ABS have similar properties and can be used at low temperatures, but they are opaque.

Styrene-butane co-polymers[edit]

Styrene-butane co-polymers can be produced with a low butene content. Styrene-butane co-polymers include PS-I and SBC (see below), both co-polymers are impact resistant. PS-I is prepared by graft co-polymerization, SBC by anionic block co-polymerization, which makes it transparent in case of appropriate block size.[53]

If styrene-butane co-polymer has a high butylene content, styrene-butadiene rubber (SBR) is formed.

The impact strength of styrene-butadiene co-polymers is based on phase separation, polystyrene and poly-butane are not soluble in each other (see Flory-Huggins theory). Co-polymerization creates a Duplicate Image Finder Quick Update v1.0.03 crack serial keygen layer without complete mixing. The butadiene fractions (the "rubber phase") assemble to form particles embedded in a polystyrene matrix. A decisive factor for the improved impact strength of styrene-butadiene copolymers is their higher absorption capacity for deformation work. Without applied force, the rubber phase initially behaves like a filler. Under tensile stress, crazes (microcracks) are formed, which spread to the rubber particles. The energy of the propagating crack is then transferred to the rubber particles along its path. A large number of cracks give DiskDigger full version Archives originally rigid material a laminated structure. The formation of each lamella contributes to the consumption of energy and thus to an increase in elongation at break. Polystyrene homo-polymers deform when a force is applied until they break. Styrene-butane co-polymers do not break at this point, but begin to flow, solidify to tensile strength and only break at much higher elongation.[54]:&#;&#;

With a high proportion of polybutadiene, the effect of the two phases is reversed. Styrene-butadiene rubber behaves like an elastomer but can be processed like a thermoplastic.

Impact-resistant polystyrene (PS-I)[edit]

PS-I (impact resistant polystyrene) consists of a continuous polystyrene matrix and a rubber phase dispersed therein. It is produced by polymerization of styrene in the presence of polybutadiene dissolved (in styrene). Polymerization takes place simultaneously in two ways:[55]

  • Graft copolymerization: The growing polystyrene chain reacts with a double bond of the polybutadiene. As a result, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, several polystyrene chains are attached to one polybutadien S represents in the figure the styrene repeat unit, B the butadiene repeat unit. However, the middle block often does not consist of such depicted butane homo-polymer but of a styrene-butadiene co-polymer:

SSSSSS&#;SSSSSSS&#;SSSSSSBBSBBSB&#;SBBBBSB&#;SSBBBSBSSSSSSS&#;SSSSSSS&#;SSSSSSSSSSSSSSSS

By using a statistical copolymer at this position, the polymer becomes less susceptible to cross-linking and flows better in the melt. For the production of SBS, the first styrene is homopolymerized via anionic copolymerization. Typically, an organometallic compound such as butyllithium is used as a catalyst. Butadiene is then added and after styrene again its polymerization. The catalyst remains active during the whole process (for which the used chemicals must be of high purity). The molecular weight distribution of the polymers is very low (polydispersity in the range ofthe individual chains have thus very similar lengths). The length of the individual blocks can be adjusted by the ratio of catalyst to monomer. The size of the rubber sections, in turn, depends on the block length, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. The production of small structures (smaller than the wavelength of the light) ensure transparency. In contrast to PS-I, however, the block copolymer does not form any particles but has a lamellar structure.

Styrene-butadiene rubber[edit]

Main article: Styrene-butadiene

Styrene-butadiene rubber (SBR) is produced like PS-I by graft copolymerization, but with a lower styrene content. Styrene-butadiene rubber thus consists of a rubber matrix with a polystyrene phase dispersed therein.[56] Unlike PS-I and SBC, it is not a thermoplastic, but an elastomer. Within the rubber phase, the polystyrene phase is assembled into domains. This causes physical cross-linking on a microscopic level. When Duplicate Image Finder Quick Update v1.0.03 crack serial keygen material is heated above the glass transition point, the domains disintegrate, the cross-linking is temporarily suspended and the material can be processed like a thermoplastic.[57]

Acrylonitrile butadiene styrene[edit]

Main article: Acrylonitrile butadiene styrene

Acrylonitrile butadiene styrene (ABS) is a material that is stronger than pure polystyrene.

Others[edit]

SMA is a copolymer with maleic anhydride. Styrene can be copolymerized with other monomers; for example, divinylbenzene can be used for cross-linking the polystyrene chains to give the polymer used in solid phase peptide synthesis. Styrene-acrylonitrile resin (SAN) has a greater thermal resistance than pure styrene.

Environmental issues[edit]

Production[edit]

Polystyrene foams are produced using blowing agents that form bubbles and expand the foam. In expanded polystyrene, these are usually hydrocarbons such as pentane, which may pose a flammability hazard in manufacturing or storage of newly manufactured material, but have relatively mild environmental impact.[citation needed] Extruded polystyrene is usually made with hydrofluorocarbons (HFCa),[58] which have global warming potentials of approximately – times that of carbon dioxide.[59]

Non-biodegradable[edit]

Waste polystyrene takes hundreds of years to biodegrade and is resistant to photo-oxidation.[60]

Litter[edit]

  • Coastal debris including polystyrene

Animals do not recognize polystyrene foam as an artificial material and may even mistake it for food.[61] Polystyrene foam blows in the wind and floats on water, due to its low specific gravity. It can have serious effects on the health of birds or marine animals that swallow significant quantities.[61] Juvenile rainbow trout exposed to polystyrene fragments have produced toxic effects by causing substantial histomorphometrical changes.[62]

Reducing[edit]

Main article: Phase-out of polystyrene foam

Restricting the use of foamed polystyrene takeout food packaging is a priority of many solid waste environmental organisations.[63] Efforts have been made to find alternatives to polystyrene, especially foam in restaurant settings. The original impetus was to eliminate chlorofluorocarbons (CFC), which was a former component of foam.

United States[edit]

InBerkeley, California, banned CFC food containers.[64] The following year, Suffolk County, New York, became the first U.S. jurisdiction to ban polystyrene in general.[65] However, legal challenges FarPoint Spread for Windows Forms v4.0.2022.for DotNET Framework v2.0 the Society of the Plastics Industry[66] kept the ban from going into effect until at last it was delayed when the Republican and Conservative parties gained the majority of the county legislature.[67] In the meantime, Berkeley became the first city to ban all foam food containers.[68] As ofabout one hundred localities in the United States, including Portland, Oregon, and San Francisco had some sort of ban on polystyrene foam in restaurants. For instance, in Oakland, California, required restaurants to switch to disposable food containers that would biodegrade if added to food compost.[69] InSan Jose became reportedly the largest city in the country to ban polystyrene foam food containers.[70] Some communities have implemented wide polystyrene bans, such as Freeport, Maine, which did so in [71] Inthe first U.S. ban of general polystyrene foam was enacted in Berkeley, California.[68]

On 1 JulyNew York City became the largest city in the United States to attempt to prohibit the sale, possession, and distribution of single-use polystyrene foam (the initial decision was overturned on appeal).[72] In San Francisco, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, supervisors approved the toughest ban on "Styrofoam" (EPS) in the US which went into effect 1 January The city's Department of the Environment can make exceptions for certain uses like shipping medicines at prescribed temperatures.[73]

The U.S. Green Restaurant Association does not allow polystyrene foam to be used as part of its certification standard.[74] Several green leaders, from the Dutch Ministry of the Environment to Starbucks's Green Team, advise people to reduce their environmental harm by using reusable coffee cups.[75]

In MarchMaryland banned polystyrene foam food containers and became the first state in the country to pass a food container foam ban through the state legislature. Maine was the first state to officially get a foam food container ban onto the books, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. In MayMaryland Governor Hogan allowed the foam ban (House Bill ) to become law without a signature making Maryland the second state to have a food container foam ban on the books, but is the first one to take effect on 1 July [76][77][78][79]

In Septemberthe New Jersey state legislature voted to ban disposable foam food containers and cups made of polystyrene foam.[80]

[edit]

China banned expanded polystyrene takeout/takeaway containers and tableware around However, compliance has been a problem and, inthe Chinese plastics industry was lobbying for the ban's repeal.[81]

India and Taiwan also banned polystyrene-foam food-service ware before [82]

The government of Zimbabwe, through its Environmental Management Agency (EMA), banned polystyrene containers (popularly called 'kaylite' in the country), under Statutory Instrument 84 of (Plastic Packaging and Plastic Bottles) (Amendment) Regulations, (No 1.) [83][84]

The city of Vancouver, Canada, has announced its Zero Waste plan in The city will Duplicate Image Finder Quick Update v1.0.03 crack serial keygen bylaw amendments to prohibit business license holders from serving prepared food in polystyrene foam cups and take-out containers, beginning 1 June [85]

Fiji passed the Environmental Management Bill in December Imports of polystyrene products was banned in January [86]

Recycling[edit]

In general, polystyrene is not accepted in curbside collection recycling programs and is not separated and recycled where it is accepted. In Germany, polystyrene is collected, as a consequence of the packaging law (Verpackungsverordnung) that requires manufacturers to take responsibility for recycling or disposing of any packaging material they sell.

Most polystyrene products are currently not recycled due to the lack of incentive to invest in the compactors and logistical systems required. Due to the low density of polystyrene foam, it is not economical to collect. However, if the waste material goes through an initial compaction process, the material changes density from typically 30&#;kg/m3 to &#;kg/m3 and becomes a recyclable commodity of high value for producers of recycled plastic pellets. Expanded polystyrene scrap can be easily added to products such as EPS insulation sheets and other EPS materials for construction applications; many manufacturers cannot obtain sufficient scrap because of collection issues. When it is not used to make more EPS, foam scrap can be turned into products such as clothes hangers, park benches, flower pots, toys, rulers, stapler bodies, seedling containers, picture frames, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, and architectural molding from recycled PS.[87] As ofaround tonnes of EPS are recycled every month in the UK.[88]

Recycled EPS is also used in many metal casting operations. Rastra is made from EPS that is combined with cement to be used as an insulating amendment in the making of concrete Duplicate Image Finder Quick Update v1.0.03 crack serial keygen and walls. American manufacturers have produced insulating concrete forms made with approximately 80% recycled EPS since

Incineration[edit]

If polystyrene is properly incinerated at high temperatures (up to &#;°C[89]) and with plenty of air[89] (14 m3/kg[citation needed]), the chemicals generated are water, carbon dioxide, and possibly small amounts of residual halogen-compounds from flame-retardants.[89] If only incomplete incineration is done, there will also be leftover carbon soot and a complex mixture of volatile compounds.[90][better&#;source&#;needed] According to the American Chemistry Council, when polystyrene is incinerated in modern facilities, the final volume is 1% of the starting volume; most of the polystyrene is converted into carbon dioxide, water vapor, and heat. Because of the amount of heat released, it is sometimes used as a power source for steam or electricity generation.[89][91]

When polystyrene was burned at temperatures of –&#;°C (the typical range of a modern incinerator), the products of combustion consisted of "a complex mixture of polycyclic aromatic hydrocarbons (PAHs) from alkyl benzenes to benzoperylene. Duplicate Image Finder Quick Update v1.0.03 crack serial keygen 90 different compounds were identified in combustion effluents from polystyrene."[92][better&#;source&#;needed] The American National Bureau of Standards Center for Fire Research found 57 chemical by-products released during the combustion of expanded polystyrene (EPS) foam.[93]

Safety[edit]

Health[edit]

The American Chemistry Council, formerly known as the Chemical Manufacturers' Association, writes:

Based on scientific tests over five decades, government safety agencies have determined that polystyrene is safe for use in foodservice products. For example, polystyrene meets the stringent standards of the U.S. Food and Drug Administration and the European Commission/European Food Safety Authority for use in packaging to store and serve food. The Hong Kong Food and Environmental Hygiene Department recently reviewed the safety of serving various foods in polystyrene foodservice products and reached the same conclusion as the U.S. FDA.[94]

From toa comprehensive review of the potential health risks associated with exposure to styrene was conducted by a member international expert panel selected by the Harvard Center for Risk Assessment. The scientists had expertise in toxicology, epidemiology, medicine, risk analysis, pharmacokinetics, and exposure assessment. The Harvard study reported that styrene is naturally present in trace quantities in foods such as strawberries, beef, and spices, and is naturally produced in the processing of foods such as wine and cheese. The study also reviewed all the published data on the quantity of styrene contributing to the diet due to migration of food packaging and disposable food contact articles, and concluded that risk to the general public from exposure to styrene from foods or food-contact applications (such as polystyrene packaging and foodservice containers) was at levels too low to produce adverse effects.[95]

Polystyrene is commonly used in containers for food and drinks. The styrene monomer (from which polystyrene is made) is a cancer suspect agent.[96] Styrene is "generally found in such low levels in consumer products that risks aren't substantial".[97] Polystyrene which is used for food contact may not contain more than 1% (% for fatty foods) of styrene by weight.[98] Styrene oligomers in polystyrene containers used for food packaging have been found to migrate into the food.[99] Another Japanese study conducted on wild-type and AhR-null mice found that the styrene trimer, which the authors detected in cooked polystyrene container-packed instant foods, may increase thyroid hormone levels.[]

Whether polystyrene can be microwaved with food is controversial. Some containers may be safely used in a microwave, but only if labeled as such.[] Some sources suggest that foods containing carotene (vitamin A) or cooking oils must be avoided.[]

Because of the pervasive use Duplicate Image Finder Quick Update v1.0.03 crack serial keygen polystyrene, these serious health related issues remain topical.[]

Fire hazards[edit]

Like other organic compounds, polystyrene is flammable. Polystyrene is classified according to DIN as a "B3" product, meaning highly inflammable or "Easily Ignited." As a consequence, although it is an efficient insulator at low temperatures, its use is prohibited in any exposed installations in building construction if the material Edraw Max 9.4.1 patch Archives not flame-retardant.[citation needed] It must be concealed behind drywall, sheet metal, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, or concrete.[] Foamed polystyrene plastic materials have been accidentally ignited and caused huge fires and losses of life, for example at the Düsseldorf International Airport and in the Channel Tunnel (where polystyrene was inside a railway carriage that caught fire).[]

See also[edit]

References[edit]

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  32. ^Doroudiani, Saeed; Chaffey, Charles E.; Kortschot, Mark T. (). "Sorption and diffusion of carbon dioxide in wood-fiber/polystyrene composites". Journal of Polymer Science Part B: Polymer Physics. 40 (8): – BibcodeJPoSBD. doi/polb
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Источник: [shoppingdowntown.us]

Instagram

American photo and video sharing social networking service

"Insta" redirects here. For the food delivery service, see Instacart. For the song by Dimitri Vegas & Like Mike, see Instagram (song).

Instagram[a] is an American photo and video sharingsocial networking service founded by Kevin Systrom and Mike Krieger. In AprilFacebook Inc. acquired the service for approximately US$1&#;billion in cash and stock. The app allows users to upload media that can be edited with filters and organized by hashtags and geographical tagging. Posts can be shared publicly or with pre-approved followers. Users can browse other users' content by tags and locations and view trending content. Users can like photos and follow other users to add their content to a personal feed.[10]

Instagram was originally distinguished by only allowing content to be framed in a square () aspect ratio with pixels to match the display width of the iPhone at the time. Inthese restrictions were eased with an increase to pixels. The service also added messaging features, the ability to include multiple images or videos in a single post, and a 'stories' feature—similar to its main opposition Snapchat—which allows users to post photos and videos to a sequential feed, with each post accessible by others for 24 hours each. As of Januarythe Stories feature is used by &#;million users daily.[10]

Originally launched for iOS in OctoberInstagram rapidly gained popularity, with one million registered users in two months, 10&#;million in a year, and 1&#;billion MixPad Multitrack Recording Software crack serial keygen of June [11] The Android version was released in Aprilfollowed by a feature-limited desktop interface in Novembera Fire OS app in Juneand an app for Windows 10 in October As of October&#;[update], over 40&#;billion photos had been uploaded. Although praised for its influence, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, Instagram has been the subject of criticism, most notably for the negative impact on teens' Renoise 2.8 Crack FREE Download health, policy and interface changes, allegations of censorship, and illegal or improper content uploaded by users.

As of Junethe most followed person is Portuguese professional footballer Cristiano Ronaldo with over &#;million followers.[12]

As of January 14,the most-liked photo on Instagram is a picture of an egg, posted by the account @world_record_egg, created with the sole purpose of surpassing the previous record of 18&#;million likes on a Kylie Jenner post. The picture currently has over 55&#;million likes.[13] The second most-liked photo is a wedding photo of Ariana Grande and her husband Dalton Gomez.[14] Instagram was the fourth most downloaded mobile app of the s.[12]

History

Instagram Icon since

See also: Timeline of Instagram

Instagram began development in San Francisco as Burbn, a mobile check-in app created by Kevin Systrom and Mike Krieger.[15] Realizing that Burbn was too similar to Foursquare, Systrom and Krieger refocused their app on photo-sharing, which had become a popular feature among Burbn users.[16][17] They renamed the app Instagram, a portmanteau of "instant camera" and "telegram".[18]

– Beginnings and major funding

On March 5,Systrom closed a $, seed funding round with Baseline Ventures and Andreessen Horowitz while working on Burbn.[19] Josh Riedel joined the company in October as Community Manager,[20] Shayne Sweeney joined in November as an engineer,[20] and Jessica Zollman joined as a Community Evangelist in August [20][21]

The first Instagram post was a photo of South Beach Harbor at Pier 38, posted by Mike Krieger at PM on July 16, [22][17] Systrom shared his first post, a picture of a dog and his girlfriend's foot, a few hours later at PM. It has been wrongly attributed as the first Instagram photo due to the earlier letter of the alphabet in its URL.[23][24][better&#;source&#;needed] On October 6,the Instagram iOS app was officially released through the App Store.[25]

In Februaryit was reported that Instagram had raised $7&#;million in Series A funding from a variety of investors, including Benchmark Capital, Jack Dorsey, Chris Sacca (through Capital fund), and Adam D'Angelo.[26] The deal valued Instagram at around $20&#;million.[27] In AprilInstagram raised $50&#;million from venture capitalists with a $&#;million valuation.[28]Joshua Kushner was the second largest investor in Instagram's Series B fundraising round, leading his investment firm, Thrive Capital, to double its money after the sale to Facebook.[29]

– Additional platforms and acquisition by Facebook

On April 3,Instagram released a version of its app for Android phones,[30][31] and it was downloaded more than one million times in less than one day.[32] The Android app has since received two significant updates: first, in Marchwhich cut the file size of the app by half and added performance improvements;[33][34] then in Aprilto add an offline mode that allows users to view and interact with content without an Internet connection. At the time of the announcement, it was reported that 80% of Instagram's &#;million users were located outside the U.S., and while the aforementioned functionality was live at its announcement, Instagram also announced its intention to make more features available offline, and that they were "exploring an iOS version".[35][36][37]

On April 9,Facebook, Inc. bought Instagram for $1&#;billion in cash and stock,[38][39][40] with a plan to keep the company independently managed.[41][42][43] Britain's Office of Fair Trading approved the deal on August 14, ,[44] and on August 22,the Federal Trade Commission in the U.S. closed its investigation, allowing the deal to proceed.[45] On September 6,the deal between Instagram and Facebook officially closed with a purchase price of $&#;million in cash and 23&#;million shares of stock.[46]

The deal closed just before Facebook's scheduled initial public offering according to CNN.[43] The deal price was compared to the $35&#;million Yahoo! paid for Flickr in [43]Mark Zuckerberg said Facebook was "committed to building and growing Instagram independently."[43] According to Wired, the deal netted Systrom $&#;million.[47]

In NovemberInstagram launched website profiles, allowing anyone to see user feeds from a web browser with limited functionality,[48] as well as a selection of badges, web widget buttons to link to profiles.[49]

Since the app's launch it had used the Foursquare API technology to provide named location tagging. In MarchInstagram started to test and switch the technology to use Facebook Places.[50][51]

– Redesign and Windows app

In Junethe desktop website user interface was redesigned to become more flat and minimalistic, but with more screen space for each photo and to resemble the layout of Instagram's mobile website.[52][53][54] Furthermore, one row of pictures only has three instead of five photos to match the mobile layout. The slideshow banner[55][56] on the top of profile pages, which simultaneously slide-showed seven picture tiles of pictures posted by the user, alternating at different times in a random order, has been removed. In addition, the formerly angular profile pictures became circular.

On May 11,Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, Instagram revamped its design, adding a black-and-white flat design theme for the app's user interface, and a less skeuomorphistic, more abstract, "modern" and colorful icon.[57][58][59] Rumors of a redesign first started circulating in April, when The Verge received a screenshot from a tipster, but at the time, an Instagram spokesperson simply told the publication that it was only a concept.[60]

On December 6,Instagram introduced comment liking. However, unlike post likes, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, the user who posted a comment does not receive notifications about comment likes in their notification inbox. Uploaders can optionally decide to deactivate comments on a post.[61][62][63]

In AprilInstagram released a Windows 10 Mobile app, after years of demand from Microsoft and the public to release an app for the platform.[64][65] The platform previously had a beta version of Instagram, first released on November 21,for Windows Phone 8.[66][67][68] The new app added support for videos (viewing and creating posts or stories, and viewing live streams), album posts and direct messages.[69] Similarly, an app for Windows 10 personal computers and tablets was released in October [70][71] In May, Instagram updated its mobile website to allow users to upload photos, and to add a "lightweight" version of the Explore tab.[72][73]

The mobile web front end allows uploading pictures since May 4, Image filters and the ability to upload videos were not introduced then.[74][75]

On April 30,the Windows 10 Mobile app was discontinued, though the mobile website remains available as a progressive web application (PWA) with limited functionality. The app remains available on Windows 10 computers and tablets, also updated to a PWA in

– IGTV, removal of the like counter, management changes

To comply with the GDPR regulations regarding data portability, Instagram introduced the ability for users to download an archive of their user data in April [76][77][78]

IGTV launched on June 20,as a standalone video application.

On September 24,Krieger and Systrom announced in a statement they would be stepping down from Instagram.[79][80] On October 1,it was announced that Adam Mosseri would be the new head of Instagram.[81][82]

During Facebook F8, it was announced that Instagram would, beginning in Canada, pilot the Duplicate Image Finder Quick Update v1.0.03 crack serial keygen of publicly-displayed "like" counts for content posted by other users.[83] Like counts would only be visible to the user who originally posted the content. Mosseri stated that this was intended to have users "worry a little bit less about how many likes they're getting on Instagram and spend a bit more time connecting with the people that they care about."[84][85] It has been argued that low numbers of likes in relativity to others could contribute to a lower self-esteem in users.[85][83] The pilot began in Mayand was extended to 6 other markets in July.[85][86] The pilot was expanded worldwide in November [87] Also in JulyInstagram announced that it would implement new features designed to reduce harassment and negative comments on the service.[88]

In AugustInstagram also began to pilot the removal of the "Following" tab from the app, which had allowed users to view a feed of the likes and comments made by users they follow. The change was made official in October, with head of product Vishal Shah stating that the feature was underused and that some users were "surprised" when they realized their activity was being surfaced in this manner.[89][90]

In OctoberInstagram introduced a limit on the number of posts visible in page scrolling mode unless logged in. Until this point, public profiles had been available to all users, even when not logged in. Following the change, after viewing a number of posts a pop-up requires the user to log in to continue viewing content.[91][92][93]

–present: New features

In MarchInstagram launched a new feature called "Co-Watching". The new feature allows users to share posts with each other over video calls. According to Instagram, they pushed forward the launch of Co-Watching in order to meet the demand for virtually connecting with friends and family due to social distancing as a result of the COVID pandemic.[94]

In AugustInstagram launched a new feature called "Reels". The feature is similar to TikTok.[95] Instagram also added suggested posts in August After scrolling through posts from the past 48 hours, Instagram displays posts related to their interests from accounts they Adobe Audition CC 2020 MAC TORRENT Archives not follow.[96]

In FebruaryInstagram began testing a new feature called Vertical Stories, said by some sources to be inspired by TikTok.[97] The same month, they also began testing the removal of ability to share feed posts to stories.[98]

In MarchInstagram launched a new feature in which four people can go live at once.[99] Instagram also announced that adults would not be allowed to message teens who don't follow them as part of a series of new child safety policies.[][][][]

In MayInstagram began allowing users in some regions to add pronouns to their profile page.[][]

On October 4,Facebook had its worst outage since The outage also affected other platforms owned by Facebook, such as Instagram and WhatsApp.[][] Security experts identified the problem as possibly being DNS-related.[]

Negative effect on teenage girls’ mental health

Facebook has known for years that its Instagram app is harmful to a number of teenagers, according to research seen by the Wall Street Journal, but the company concealed the knowledge from lawmakers.[]

Internal Facebook presentations seen by the WSJ in show that Instagram is toxic to a sizable percentage of its users, particularly teenage girls. More than 40% of Instagram’s users are under 23 years old.

“We make body image issues worse for one in three teen girls,” said a slide from a presentation. “Teens blame Instagram for increases in the rate of anxiety and depression,” said another. “This reaction was unprompted and consistent across all groups.”

The presentations were seen by the company’s executives and the findings mentioned to Mark Zuckerberg in But when asked in March about Instagram’s effect on young people, Zuckerberg defended the company’s plan to launch an Instagram product for children under

When asked by senators for its internal findings on the impact of Instagram on youth mental health, Facebook sent a six-page letter but did not include the company’s research. The company told Forbes its research is “kept confidential to promote frank and open dialogue and brainstorming internally.”[]

In a blog post, Instagram said the WSJ story "focuses on a limited set of findings and casts them in a negative light."[]

On September 27,weeks after the WSJ report was released, Facebook announced it "paused" development of Instagram Kids, the Instagram product aimed at children. The company stated it was looking into concerns raised by the regulators and parents. Adam Mosseri stated that the company would return to the project as "[t]he reality is that kids are already online, and we believe that developing age-appropriate experiences designed specifically for them is far better for parents than where we are today."[][]

Features and tools

An original photograph (left) is automatically cropped to a square by Instagram, and has a filter added at the selection of the user (right).
A photo collage of an unprocessed image (top left) modified with the 16 different Instagram filtersavailable in

Users can upload photographs and short videos, follow other users' feeds,[] and geotag images with the name of a location.[] Users can set their account as "private", Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, thereby requiring that they approve any new follower Microsoft Windows Vista Home Premium | by InvisibleQuantum keygen Users can connect their Instagram account to other social networking sites, enabling them to share uploaded photos to those sites.[] In Septembera new version of the app included new and live filters, instant tilt–shift, high-resolution photographs, optional borders, one-click rotation, and an updated icon.[][] Photos were initially restricted to a square, aspect ratio; since Augustthe app supports portrait and widescreen aspect ratios as well.[][][] Users could formerly view a map of a user's geotagged photos. The feature was removed in Septemberciting low usage.[][]

Since Decemberposts can be "saved" into a private area of the app.[][] The feature was updated in April to let users organize saved posts into named collections.[][] Users can also "archive" their posts in a private storage area, out of visibility for the public and other users. The move was seen as a way to prevent users from deleting photos that don't garner a desired number of "likes" or are deemed boring, but also as a way to limit the "emergent behavior" of deleting photos, which deprives the service of content.[][] In August, Instagram announced that it would start organizing comments into threads, letting users more easily interact with replies.[][]

Since Februaryup to ten pictures or videos can be included in a single post, with the content appearing as a swipeable carousel.[][] The feature originally limited photos to the square format, but received an update in August to enable portrait and landscape photos instead.[][]

In AprilInstagram launched its version of a portrait mode called "focus mode," which gently blurs the background of a photo or video while keeping the subject in focus when selected.[] In November, Instagram began to support Alt text to add descriptions of photos for the visually impaired. They are either generated automatically using object Duplicate Image Finder Quick Update v1.0.03 crack serial keygen (using existing Facebook technology) or manually specified by the uploader.[]

On March 1,Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, Instagram launched a new feature named Instagram Live "Rooms" Let Four People Go Live Together.[]

In MayInstagram announced a new accessibility feature for videos on Instagram Reels and Stories to allow creators to place closed captions on their content.[]

Hashtags

In JanuaryInstagram introduced hashtags to help users discover both photos and each other.[][] Instagram encourages users to make tags both specific and relevant, rather than tagging generic words like "photo", to make photographs stand out and to attract like-minded Instagram users.[]

Users on Instagram have created "trends" through hashtags. The trends deemed the most popular on the platform often highlight a specific day of the week to post the material on. Examples of popular trends include #SelfieSunday, in which users post a photo of their faces on Sundays; #MotivationMonday, in which users post motivational photos on Mondays; #TransformationTuesday, in which users post photos highlighting differences from the past to the present; #WomanCrushWednesday, in which users post photos of women they have a romantic interest in or view favorably, as well as its #ManCrushMonday counterpart centered on men; and #ThrowbackThursday, in which users post a photo from their past, highlighting a particular moment.[][]

In DecemberInstagram began to allow users to follow hashtags, which display relevant highlights of the topic in their feeds.[][]

Explore

In JuneInstagram introduced "Explore", a tab inside the app that displays popular photos, photos taken at nearby locations, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, and search.[] The tab was updated in June to feature trending tags and places, curated content, and the ability to search for locations.[] In AprilInstagram added a "Videos You Might Like" channel to the tab,[][] followed by an "Events" channel in August, featuring videos from concerts, sports games, and other live events,[][] followed by the addition of Instagram Stories in October.[][] The tab was later expanded again in November after Instagram Live launched to display an algorithmically-curated page of the "best" Instagram Live videos currently airing.[] In MayInstagram once again updated the Explore tab to promote public Stories content from nearby places.[]

Photographic filters

Instagram offers a number of photographic filters that users can apply to their images. In FebruaryInstagram added a "Lux" filter, an effect that "lightens shadows, darkens highlights and increases contrast".[][] In DecemberSlumber, Crema, Ludwig, Aden, and Perpetua were five new filters to be added to the Instagram filter family.[]

Video

Initially a purely photo-sharing service, Instagram incorporated second video sharing in June [][] The addition was seen by some in the technology media as Facebook's attempt at competing with the then-popular video-sharing application Vine.[][] In AugustInstagram added support for widescreen videos.[][] In MarchInstagram increased the second video limit to 60 seconds.[][] Albums were introduced in Februarywhich allow up to 10 minutes of video to be shared in one post.[][][]

IGTV

Main article: IGTV

IGTV is a vertical video&#;application launched by Instagram[] in June Basic functionality is also available within the Instagram app and website. IGTV allows uploads of up to 10 minutes in length with a file size of up to MB, with verified and popular users allowed to upload videos of up to 60 minutes in length with a file size of up to GB.[] The app automatically begins playing videos as soon as it is launched, which CEO Kevin Systrom contrasted to video hosts where one must first locate a video.[][][]

Reels

In Novemberit was reported that Instagram had begun to pilot a new video feature known as "Reels" in Brazil, expanding to France and Germany afterwards.[] It is similar in functionality to the Chinese video-sharing service TikTok, with a focus on allowing users to record short videos set to pre-existing sound clips from other posts.[] Users could make up to 15 (later 30) second videos using this feature.[] Reels also integrates with existing Instagram filters and editing tools.[]

In JulyInstagram rolled out Reels to India after TikTok was banned in the country.[] The following month, Reels officially launched in 50 countries including the United States, Canada and United Kingdom.[] Instagram has recently introduced a reel button on home page.[]

On June 17,Instagram launched full-screen advertisements in Reels. The ads are similar to regular reels and can run up to 30 seconds. They are distinguished from regular content by the "sponsored" tag under the account name.[]

Instagram Direct

In DecemberInstagram announced Instagram Direct, a feature that lets users interact through private messaging. Users who follow each other can send private messages with photos and videos, in contrast to the public-only requirement that was previously in place. When users receive a private message from someone they don't follow, the message is marked as pending and the user must accept to see it. Users can send a photo to a maximum of 15 people.[][][] The feature received a major update in Septemberadding conversation threading and making it possible for users to share locations, hashtag pages, and profiles through private messages directly from the news feed. Additionally, users can now reply to private messages with text, emoji or by clicking on a heart icon. A camera inside Direct lets users take a photo and send it to the recipient without leaving the conversation.[][][] A new update in November let users make their private messages "disappear" after being viewed by the recipient, with the sender receiving a notification if the recipient takes a screenshot.[][]

In AprilInstagram redesigned Direct to combine all private messages, both permanent and ephemeral, into the same message Duplicate Image Finder Quick Update v1.0.03 crack serial keygen In May, Instagram made it possible to send website links in messages, and also added support for sending photos in their original portrait or landscape orientation without cropping.[][]

In AprilDirect became accessible from the Instagram website, allowing users to send direct messages from a web version using WebSocket technology.[]

In AugustFacebook started merging Instagram Direct into Facebook Messenger. After the update (which is rolled out to a segment of the user base) the Instagram Direct icon transforms into Facebook Messenger icon.[]

In Marcha feature was added that prevents adults from messaging users under 18 who do not follow them as part of a series of new child safety policies.[][][]

Instagram Stories

In AugustInstagram launched Instagram Stories, a feature that allows users to take photos, add effects and layers, and add them to their Instagram story. Images uploaded to a user's story expire after 24 hours. The media noted the feature's similarities to Snapchat.[][] In response to criticism that it copied functionality from Snapchat, CEO Kevin Systrom told Recode that "Day One: Instagram was a combination of Hipstamatic, Twitter [and] some stuff from Facebook like the 'Like' button. You can trace the roots of every feature anyone has in their app, somewhere in the history of technology". Although Systrom acknowledged the criticism as "fair", Recode wrote that "he likened the two social apps' common features to the auto industry: Multiple car companies can coexist, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, with enough differences among them that they serve different consumer audiences". Systrom further stated that "When we adopted [Stories], we decided that one of the really annoying things about the format is that it just kept going and you couldn't pause it to look at something, you couldn't rewind. We did all that, we implemented that." He also told the publication that Snapchat "didn't have filters, originally. They adopted filters because Instagram had filters and a lot of others were trying to adopt filters as well."[][]

In November, Instagram added live video functionality to Instagram Stories, allowing users to broadcast themselves live, with the video disappearing immediately after ending.[][]

In JanuaryInstagram launched skippable ads, where five-second photo and second video ads appear in-between different stories.[][][]

In AprilInstagram Stories incorporated augmented reality stickers, a "clone" of Snapchat's functionality.[][][]

In MayInstagram expanded the augmented reality sticker feature to support face filters, letting users add specific visual features onto their faces.[][]

Later in May, TechCrunch reported about tests of a Location Stories feature in Instagram Stories, where public Stories content at a certain location are compiled and displayed on a business, landmark or place's Instagram page.[] A few days later, Instagram announced "Story Search", in which users can search for geographic locations or hashtags and the app displays relevant public Stories content featuring the search term.[][]

In JuneInstagram revised its live-video functionality to allow users to add their live broadcast to their story for availability in the next 24 hours, or discard the broadcast immediately.[] In July, Instagram started allowing users to respond to Stories content by sending photos and videos, complete with Instagram effects such as filters, stickers, and hashtags.[][]

Stories were made available for viewing on Instagram's mobile and desktop websites in late August [][]

On December 5,Instagram introduced "Story Highlights",[] also known as "Permanent Stories", which are similar to Instagram Stories, but don't expire. They appear as circles below the profile picture Duplicate Image Finder Quick Update v1.0.03 crack serial keygen biography and are accessible from the desktop website as well.

In Junethe daily active story users of Instagram had reached &#;million users, and monthly active users had reached 1&#;billion active users.[]

Advertising

Emily White joined Instagram as Director of Business Operations in April [][] She stated in an interview with The Wall Street Journal in September that the company Duplicate Image Finder Quick Update v1.0.03 crack serial keygen be ready to begin selling advertising by September as a way to generate business from a popular entity that had not yet created profit for its parent company.[] White left Instagram in December to join Snapchat.[][] In AugustJames Quarles became Instagram's Global Head of Business and Brand Development, tasked with overseeing advertisement, sales efforts, and developing new "monetization products", according to a spokesperson.[]

In OctoberInstagram announced that video and image ads would soon appear in feeds for users in the United States,[][] with the first image advertisements displaying on November 1, [][] Video ads followed nearly a year later on October 30, [][] In JuneInstagram announced the rollout of ads in the United Kingdom, Canada and Australia,[] with ads starting to roll out that autumn.[]

In MarchInstagram announced it would implement "carousel ads," allowing advertisers to display multiple images with options for linking to additional content.[][] The company launched carousel image ads in October ,[][] and video carousel ads in March []

In MayInstagram launched new tools for business accounts, including business profiles, analytics and the ability to promote posts as ads. To access the tools, businesses had to link a corresponding Facebook page.[] The new analytics page, known as Instagram Insights, allowed business accounts to view top posts, reach, impressions, engagement and demographic data.[] Insights rolled out first in the United States, Australia, and New Zealand, and expanded to the rest of the world later in [][][]

In FebruaryInstagram announced that it had ,&#;advertisers on the platform.[] This number increased toby September ,[] and 1&#;million in March [][]

In NovemberInstagram added the ability for business accounts to add product links directing users to a purchase page or to save them to a "shopping list."[] In AprilInstagram added the option to "Checkout on Instagram," which allows merchants to sell products directly through the Instagram app.[]

In Marchvia a blog post, Instagram announced that they are making major moderation changes in order to decrease the flow of disinformation, hoaxes and fake news regarding COVID on its platform, "We'll remove COVID accounts from account recommendations, and we are working to remove some COVID related content from Explore unless posted by a credible health organization. We will also start to downrank content in feed and Stories that has been rated false by third-party fact-checkers."[]

In JuneInstagram launched a native affiliate marketing tool creators can use to earn commissions based on sales. Commission-enabled posts are labeled "Eligible for Commission" on the user side to identify them as affiliate posts. Launch partners included Sephora, MAC, and Kopari.[]

Stand-alone apps

Instagram has developed and released three stand-alone apps with specialized functionality. In Julyit released Bolt, a messaging app where users click on a friend's profile photo to quickly send an image, with the content disappearing after being seen.[][] It was followed by the release of Hyperlapse in August, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen iOS-exclusive app that uses "clever algorithm processing" to create tracking shots and fast time-lapse videos.[][] Microsoft launched a Hyperlapse app for Android and Windows in Maybut there has been no official Hyperlapse app from Instagram for either of these platforms to date.[] In Octoberit released Boomerang, a video app that combines photos into short, one-second videos that play back-and-forth in a loop.[][]

Third-party services

The popularity of Instagram has led to a variety of third-party services designed to integrate with it, including services for creating content to post on the service and generating content from Instagram photos (including physical print-outs), analytics, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, and alternative clients for platforms with insufficient or no official support from Instagram (such as in the past, iPads).[][]

In NovemberInstagram Duplicate Image Finder Quick Update v1.0.03 crack serial keygen that effective June 1,it would end "feed" API access to its platform in order to "maintain control for the community and provide a clear roadmap for developers" and "set up a more sustainable environment built around authentic experiences on the platform", including those oriented towards content creation, publishers, and advertisers. Additionally, third-party clients have been prohibited from using the text strings "insta" or "gram" in their name.[] It was reported that these changes were primarily intended to discourage third-party clients replicating the entire Instagram experience (due to increasing monetization of the service), and security reasons (such as preventing abuse by automated click farms, and the hijacking of accounts). In the wake of the Cambridge Analytica scandal, Instagram began to impose further restrictions on its API in [][][]

For unlimited browsing of public Instagram profiles without having to create an account, as well as for anonymous browsing of someone else's Stories, has to use the Instagram profiles viewer.[] Stories are more authentic than typical photos posted as posts because users know that in 24 hours their Stories will disappear if they don't add them as highlighted[] (however users can check who saw their Story for 48 hours after it was published[]). For this reason, they are very valuable for market Duplicate Image Finder Quick Update v1.0.03 crack serial keygen checking

On December 16,Facebook announced it would expand its fact checking programs towards Instagram,[] by using third-party fact-checkers organizations false information is able to be identified, reviewed and labeled as false information. Content when rated as false or partly false is removed from the explore page and hashtag pages, additionally content rated as false or partly false are labeled as such. With the addition of Facebook fact-checking program came the use of image matching technology to find further instances of misinformation. If a piece of content is labeled false or partly false on Facebook or Instagram then duplicates of such content will also be labeled as false.[]

Algorithm and design changes

In AprilInstagram began rolling out a change to the order of photos visible in a user's timeline, shifting from a strictly chronological order to one determined by an algorithm.[] Instagram said the algorithm was designed so that users would see more of the photos by users that they liked,[] but there was significant negative feedback, with many users asking their followers to turn on post notifications in order to make sure they see updates.[][][] The company wrote a tweet to users upset at the prospect of the change, but did not back down,[] nor provide a way to change it back, which they re-affirmed in [][]

SinceInstagram has employed the ability to reduce the prominence of accounts ("shadowbanning") it believes may be generating non-genuine engagement and spam (including excessive use of unneeded hashtags), preventing posts from appearing in search results and in the app's Explore section. In a now-deleted Facebook post, Instagram wrote that "When developing content, we recommend focusing on your business objective or goal rather than hashtags".[][] Instagram has since been accused of extending the practice to censor posts under vague and inconsistent circumstances, particularly in regards to sexually suggestive material.[]

Instagram caused the userbase to fall into outrage with the December update.[][][][][] They found an attempt to alter the flow of the feed from the traditional vertical scroll to emulate and piggy-back the popularity of their Instagram Stories with a horizontal scroll, by swiping left.[] Various backtracking statements were released explaining it as a bug, or as a test release that had been accidentally deployed to too large an audience.[][]

In NovemberInstagram replaced the activity feed tab with a new "Shop" tab, moving the activity feed to the top. The "new post" button was also relocated to the top and replaced with a Reels tab[] The company states that "the Shop tab gives you a better way to connect with brands and creators and discover products you love" and the Reels tab "makes it easier for you to discover short, fun videos from creators all over xlstat license key 2020 Archives world and people just like you."[] However, users have not responded well to the change, taking their complaints to Twitter and Reddit, and The New York Times has shunned Reels in particular, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, saying "Not only does Reels fail in every way as a TikTok clone, but it’s confusing, frustrating and impossible to navigate".[]

Also inInstagram rolled out a feature titled "suggested posts", which adds posts from accounts Instagram thinks a user would like to such user's feed.[] The feature was met with controversy from both Reddit users[] from The Verge, which reported that suggested posts would keep users glued to their feed, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, give Instagram more advertising space, and ultimately harm the mental health of users, while Instagram executive Julian Gutman rebutted, stating the feature was not intended to keep users glued to their screens.[] Suggested posts received more controversy after Fast Company stated that the feature would be impossible to turn off.[]

On 23 JuneInstagram announced a test change to the "suggested posts" feature. The company will put suggested posts ahead of posts from people that the user is following in the Instagram feed, citing positive reception as the reason for this change.[]

Impact on people

Mental health

Depression

Khodarahimi & Fathi found evidence for Instagram users displaying higher levels of depressive symptoms.[] Frison & Eggermont pointed out that only Instagram browsing, and not Instagram liking nor posting, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, predicts more depressive symptoms.[] It also provides evidence for a relation between Instagram use and depressive symptomatology in the opposite direction, where level of depressed mood has shown to positively predict Instagram posting. Lamp et al showed a positive relationship between depression and the number of selfies taken before posting it on Instagram.[]

Anxiety

Khodarahimi & Fathi observed higher levels of anxiety in Instagram users compared to non-users,[] while Mackson et al suggested beneficial effects of Instagram use on anxiety symptoms.[] Multiple studies pointed out small to moderate positive relationships between time spent on Instagram and trait anxiety, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, physical appearance anxiety, social anxiety and attention to high insecurity-eliciting body regions.[][][][]

Stress

A paper showed that users who feel that they spend too much time on Instagram report higher levels of Instagram addiction, which in turn was related to higher self-reported levels of Instagram induced stress.[][]

Addiction

In a study focusing on the relationship between various psychological needs and Instagram addiction by students, Foroughi et al found that the desire for recognition and entertainment were predictors of students' addition to Instagram. In addition, the study proved that Instagram addiction negatively affect academic performance.[] Gezgin & Mihci quantified Turkish student's Instagram use's contribution to overall smartphone addiction, and concluded that frequent instagraming correlates with addiction to smartphone.[]

Satisfaction with appearance

Sherlock & Wagstaff showed that both the number of followers and followees show a small positive relationship with trait anxiety.[] Instagram users report higher body surveillance,[] appearance related pressure,[] eating pathology[] and lower body satisfaction[] than non-users.[] Multiple studies have shown that users who take more selfies (before posting) and strategically present themselves on Instagram, for example by editing or manipulating selfies, report higher levels of body surveillance, body dissatisfaction, and lower body esteem.[][][][] Tiggemann et al also confirmed this through experimental study, finding that taking and editing selfies led to higher facial dissatisfaction.[][]

False self-presentation

In a study Mun & Kim pointed out that Instagram users with a strong need for approval were more likely to create Duplicate Image Finder Quick Update v1.0.03 crack serial keygen presentation of themselves on their Instagram accounts, which in turn increased the likelihood of depression, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. Notably, depression was mitigated by the perception of popularity.[]

Body image

Multiple studies confirmed that Instagram usage is associated with body surveillance and body self-image. In particular, following appearance-focused Instagrammers corresponded with the desire to look thin. Comments related to appearance on Instagram are leading to higher dissatisfactions with one’s body.[][][][] Based on Facebook's leaked internal research, Instagram has negative effects on the body image of one in three teenagers.[] Leaked internal documents also indicate that two thirds of teen girls and 40 percent of teen boys experience negative social comparison, and that Instagram makes 20 percent of the teens feel worse about themselves. According to the leaked research, Instagram has higher impact on appearance comparison than TikTok or Snapchat.[]

Loneliness

Mackson et al found that Instagram users were less lonely than non-users [] and that Instagram membership predicts lower self-reported loneliness.[]

Social exclusion

In a study by Büttnera et Rudertb[] pointed out that not being tagged in an Instagram photo triggers the feeling of social exclusion and ostracism, especially for those with higher needs to belong, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen.

Wellbeing

The relationship between Instagram usage intensity and wellbeing varies by wellbeing indicator. Brailovskaia & Margraf found a significant positive relationship between Instagram membership and extraversion, life satisfaction, and social support. The association between Instagram membership and conscientiousness was marginally significantly negative. The same study showed a positive relationship between extraversion, life satisfaction, social support and Instagram membership.[]

Life satisfaction

Fioravanti et al showed that women who had to take a break from Instagram for seven days reported higher life satisfaction compared to women who continued their habitual pattern of Instagram use. The effects seemed to be specific for women, where no significant differences were observed for men.[]

Alcohol and drug use

Instagram usage intensity shows a small positive correlation with alcohol consumption, with binge drinkers reporting greater intensity of Instagram use than non-binge drinkers.[] An earlier study examined the relationship between alcohol consumption during college. It found a small to moderate positive relationship between alcohol consumption and Instagram usage, enhanced drinking motives, and drinking behavior.[]

Fear of Missing Out

The relationship between Instagram use and the fear of missing out (FoMo) has been confirmed in multiple studies.[][] Use intensity shows a strong, while the number of followers and followees shows a weak correlation with FoMo. Research shows that Instagram browsing predicts social comparison, which generates FoMo, and FoMo can ultimately lead to depression.[]

Eating disorders

A comparison of Instagram users with non-users showed that boys with an Instagram account differ from boys without an account in terms of over-evaluation of their shape and weight, skipping meals, and levels of reported disordered eating cognitions. Girls with an Instagram account also differed from girls without an account in terms of skipping meals. However, none of the other associations Duplicate Image Finder Quick Update v1.0.03 crack serial keygen were reported for boys were observed for girls. Instead, girls with an Instagram account differed from girls without an account in that they used a stricter exercise schedule. This suggests a possible differential effect of Instagram membership on body (dis)satisfaction and disordered eating for boys and girls.[][] Regarding the relationship between time spent on Instagram and body image and/or disordered eating, several body-related constructs were consistently linked to indicators of Instagram use. More specifically, several studies identified a small positive relationship between time spent on Instagram and both internalization of beauty ideals or muscular ideals, and self-objectification across studies.[][][][] A positive link has been pointed out between the intensity of Instagram use and both body surveillance and dietary behaviors or disordered eating.[][]

Suicide and self-harm

Picardo et al examined the relationship between self-harm posts and actual self-harm behaviours offline and found such content had negative emotional effects on some users and reported preliminary evidence of potential harmful effects in relation to self-harm related behaviours offline, although causal effects cannot be claimed. At the same time, some benefits for those who engage with self-harm content online have been suggested.[] Instagram has published content to help users in need to get support.[]

Based on Facebook's leaked internal research, 13 percent of British teenager users with suicidal thoughts could trace these thoughts to Instagram use. Amongst teenagers in the US with suicidal thoughts, this number is much smaller - 6 percent.[]

Impact on businesses

Instagram can help promote commercial products and services. It can be distinguished from other social media platforms by its focus on visual communication. Instagram marketing is an effective way to advertise a product, given that a picture is said to speak a thousand words.[] The platform can also help commercial entities save branding costs, as it can be used for free even for commercial purposes.

User characteristics and behavior

The Instagram app, running on the Androidoperating system

Users

See also: List of most-followed Instagram accounts

Following the release in October, Instagram had one million registered users in December [][] In Juneit announced that it had 5&#;million users,[] which increased to 10&#;million in September.[][] This growth continued to 30&#;million users in April ,[][30] 80&#;million in July ,[][] &#;million in February ,[][] &#;million in June ,[] &#;million in September ,[][] &#;million in December ,[][] &#;million in September ,[][] &#;million in June ,[][] &#;million in December ,[][] &#;million in April ,[][] and &#;million in September [][]

In OctoberInstagram Stories reached &#;million active users, two months after launch.[][] This increased to &#;million in January ,[][] &#;million in April, surpassing Snapchat's user growth,[][][] and &#;million active users in June [][]

In AprilInstagram Direct had &#;million monthly users.[][][]

In JuneInstagram passed &#;million photos uploaded to the service.[][] This grew to &#;million in August ,[][] and by Junethere were over 16&#;billion photos on the service.[] In Octoberthere existed over 40&#;billion photos.[]

Demographics

As of [update], Instagram's users are divided equally with 50% iPhone owners and 50% Android owners. While Instagram has a neutral gender-bias format, 68% of Instagram users are female while 32% are male. Instagram's geographical use is shown to favor urban areas as 17% of US adults who live in urban areas use Instagram while only 11% of adults in suburban and rural areas do so. While Instagram may appear to be one of the ReiBoot Pro windows Archives widely used sites for photo sharing, only 7% of daily photo uploads, among the top four photo-sharing platforms, come from Instagram. Instagram has been proven to attract the younger generation with 90% of the &#;million users under the age of From June to JuneInstagram approximately doubled their number of users. With regards to income, 15% of US Internet users who make less than $30, per year use Instagram, while 14% of those making $30, to $50, and 12% of users who make more than $50, per year do so.[] With respect to the education demographic, respondents with some college education proved to be the most active on Instagram with 23%. Following behind, college graduates consist of 18% and users with a high school diploma or less make up 15%. Among these Instagram users, 24% say they use the app several times a day.[]

User behavior

Ongoing research continues to explore how media content on the platform affects user engagement. Past research has found that media which show peoples' faces receive more 'likes' and comments and that using filters that increase warmth, exposure, and contrast also boosts engagement.[] Users are more likely to engage with images that depict fewer individuals compared to groups and also are more likely to engage with content that has not been watermarked, as they view this content as less original and reliable compared to user-generated content.[] Recently Instagram has come up with an option for users to apply for a verified account badge; however, this does not guarantee every user who applies will get the verified blue tick.[]

The motives for using Instagram among young people are mainly to look at posts, particularly for the sake of social interactions and recreation. In contrast, the level of agreement expressed in creating Instagram posts was lower, which demonstrates that Instagram's emphasis on visual communication is widely accepted by young people in social communication.[]

Reception

InWashington Post reported that it has made an international black market for migrant workers, women in Africa and Asia, sold into servitude as maids in Persian Gulf countries.[]

Awards

Instagram was the runner-up for "Best Mobile App" at the TechCrunch Crunchies in January [] In MayFast Company listed CEO Kevin Systrom at number 66 in "The Most Creative People in Business in ".[] In JuneInc. included co-founders Systrom and Krieger in its "30 Under 30" list.[15]

Instagram won "Best Locally Made App" in the SF Weekly Web Awards in September []7x7Magazine's September issue featured Systrom and Krieger on the cover of their "The Hot 20 " issue.[] In DecemberApple Inc. named Instagram the "App of the Year" for [] InInstagram was named No. 1 by Mashable on its list of "The best iPhone apps of all time," noting Instagram as "one of the most influential social networks in the world."[] Instagram was listed among Time's "50 Best Android Applications for " list.[]

Mental health

See also: Social media and suicide

In Maya survey conducted by the United Kingdom's Royal Society for Public Health, featuring 1, people aged 14–24, asking them to rate social media platforms depending on anxiety, depression, loneliness, bullying and body image, concluded that Instagram was the "worst for young mental health". Some have suggested it may contribute to digital dependence, whist this same survey noticed its positive effects, including self-expression, self-identity, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, and community building. In response to the survey, Instagram stated that "Keeping Instagram a safe and supportive place for young people was a top priority".[][] The company filters out the reviews and accounts. If some of the accounts violate Instagram's community guidelines, it will take action, which could include banning them.[]

Inresearchers from Harvard University and University of Vermont demonstrated a machine learning tool that successfully outperformed general practitioners' diagnostic success rate for depression. The tool used color analysis, metadata components, and face detection of users' feeds.[]

ThroughoutInstagram began to test the hiding of like counts for posts made by its users.

Correlations have been made between Instagram content and poor body dissatisfaction, as a result of body comparisons, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. In a recent survey half of the applicants admitted to photo editing behavior which has been linked with concerns over body image.[]

In OctoberCNN published an article and interviews on how two young women, Ashlee Thomas and Anastasia Vlasova, say Instagram endangered their lives by Instagram having toxic effects on their diets.[]

In response to abusive and negative comments on users' photos, Instagram has made efforts to give users more control over their posts and accompanying comments field. In Julyit announced that users would be able to turn off comments for their posts, as well as control the language used in comments by inputting words they consider offensive, which will ban applicable comments from showing up.[][] After the July announcement, 5DFly Photo Design crack serial keygen ability to ban specific words began rolling out early August to celebrities,[] followed by regular users in September.[] In December, the company began rolling out the abilities for users to turn off the comments and, for private accounts, remove followers.[][]

In Septemberthe company announced that public users would be able to limit who can comment on their content, such as only their followers or people they follow. At the same time, it updated its automated comment filter to support additional languages.[][]

In JuneInstagram announced that it would automatically attempt to filter offensive, harassing, and "spammy" comments by default. The system is built using a Facebook-developed deep learning algorithm known as DeepText (first implemented on the social network to detect spam comments), which utilizes natural-language processing techniques, and can also filter by user-specified keywords.[][][]

In Julythe service announced that it would introduce a system to proactively detect problematic comments and encourage the user to reconsider their comment, as well as allowing users the ability to "restrict" others' abilities to communicate with them, citing that younger users felt the existing block system was too much of an escalation.[88]

Culture

On August 9,English musician Ellie Goulding released a new music video for her song "Anything Could Happen." The video only contained fan-submitted Instagram photographs that used various filters to represent words or lyrics from the song, and over 1, different photographs were submitted.[]

Security

In Augustreports surfaced that a bug in Instagram's developer tools had allowed "one or more individuals" Duplicate Image Finder Quick Update v1.0.03 crack serial keygen gain access to the contact information, specifically email addresses and phone numbers, of several high-profile verified accounts, including its most followed user, Selena Gomez. The company said in a Duplicate Image Finder Quick Update v1.0.03 crack serial keygen that it had "fixed the bug swiftly" and was running an investigation.[][] However, the following month, more details emerged, with a group of hackers selling contact information online, with the affected number of accounts in the "millions" rather than the previously-assumed limitation on verified accounts. Hours after the hack, a searchable database was posted online, charging $10 per search.[]The Daily Beast was provided with a sample of the affected accounts, and could confirm that, while many of the email addresses could be found with a Google search in public sources, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, some did not return relevant Google search results and thus were from private sources.[]The Verge wrote that cybersecurity firm RepKnight had found contact information for multiple actors, musicians, and athletes,[] and singer Selena Gomez's account was used by the Borderlands For PC Complete Edition Highly Compressed Free Download to post naked photos of her ex-boyfriend Justin Bieber. The company admitted that "we cannot determine which specific accounts may have been impacted", but believed that "it was a low percentage of Instagram accounts", though TechCrunch stated in its report that six million accounts were affected by the hack, and that "Instagram services more than million accounts; six million is not a small number".[]

InApple pulled an app that let users stalk people on Instagram by scraping accounts and collecting data.[]

Iran has DPI blocking for Instagram.[]

Content ownership

On December 17,Instagram announced a change to its Terms of Service policy, adding the following sentence:[]

To help us deliver interesting paid or sponsored content or promotions, you agree that a business or other entity may pay us to display your username, likeness, photos (along with any associated metadata), and/or actions you take, in connection with paid or sponsored content or promotions, without any compensation to you.

There was no option for users to opt out of the changed Terms of Service without deleting their accounts before the new policy went into effect on January 16, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, [] The move garnered severe criticism from users,[][] prompting Instagram CEO Kevin Systrom to write a blog post one day later, announcing that they would "remove" the offending language from the policy, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. Citing misinterpretations about its intention to "communicate that we'd like to experiment with innovative advertising that feels appropriate on Instagram", Systrom also stated that it was "our mistake that this language is confusing" and that "it is not our intention to sell your photos". Furthermore, he wrote that they would work on "updated language in the terms to make sure this is clear".[][]

The policy change and its backlash caused competing photo services to use the opportunity to "try to lure users away" by promoting their privacy-friendly services,[] and some services experienced substantial gains in momentum and user growth following the news.[] On December 20, Instagram announced that the advertising section of the policy would be reverted to its original October version.[]The Verge wrote about that policy as well, however, noting that the original policy gives the company right to "place such advertising and promotions on the Instagram Services or on, about, or in conjunction with your Content", meaning that "Instagram has always had the right to use your photos in ads, almost any way it wants. We could have had the exact same freakout last week, or a year ago, or the day Instagram launched".[]

The policy update also introduced an arbitration clause, which remained even after the language pertaining to advertising and user content had been modified.[]

Facebook acquisition as a violation of US antitrust law

Columbia Law School professor Tim Wu has given public talks explaining that Facebook's purchase of Instagram was a felony.[] A New York Post article published on February 26,reported that "the FTC had uncovered [a document] by a high-ranking Facebook executive who said the reason the Duplicate Image Finder Quick Update v1.0.03 crack serial keygen was buying Instagram was to eliminate a potential competitor".[] As Wu explains, this is a violation of US antitrust law (see monopoly). Wu stated that this document was an email directly from Mark Zuckerberg, whereas the Post article had stated that their source had declined to say whether the high-ranking executive was the CEO. The article reported that the FTC "has formed a task force to review "anticompetitive conduct" in the tech world amid concerns that tech companies are growing Duplicate Image Finder Quick Update v1.0.03 crack serial keygen powerful. The task force will look at "the full panoply of remedies" if it finds "competitive harm," FTC competition bureau director Bruce Hoffman told reporters."

Algorithmic advertisement with a rape threat

InOlivia Solon, a reporter for The Guardian, posted a screenshot to her Instagram profile of an email she had received containing threats of rape and murder towards her. The photo post had received three likes and countless comments, and in Septemberthe company's algorithms turned the Duplicate Image Finder Quick Update v1.0.03 crack serial keygen into an advertisement visible to Solon's sister. An Instagram spokesperson apologized and told The Guardian that "We are Duplicate Image Finder Quick Update v1.0.03 crack serial keygen this happened – it's not the experience we want someone to have. This notification post was surfaced as part of an effort to encourage engagement on Instagram. Posts are generally received by a small percentage of a person's Facebook friends." As noted by the technology media, the incident occurred at the same time parent company Facebook was under scrutiny for its algorithms and advertising campaigns being used for offensive and negative purposes.[][]

Censorship and restricted content

According to a Facebook spokesperson, on January 11,Instagram and its parent company Facebook, Inc. are removing posts "that voice support for slain Iranian commander Qassem Soleimani to comply with US sanctions".[]

Illicit drugs

Instagram has been the subject of criticism due to users publishing images of drugs they are selling on the platform. Inthe BBC discovered that users, mostly located in the United States, were posting images of drugs they were selling, attaching specific hashtags, and then completing transactions via instant messaging applications such as WhatsApp. Corresponding hashtags have been blocked as part of the company's response and a spokesperson engaged with the BBC explained:[][]

Instagram has a clear set of rules about what is and isn't allowed on the site. We encourage people who come across illegal or inappropriate content to report it to us using the built-in reporting tools next to every photo, video or comment, so we can take action. People can't buy things on Instagram, we are simply a place where people share photos and videos.

However, new incidents of illegal drug trade have occurred in the aftermath of the revelation, with Facebook, Inc., Instagram's parent company, asking users who come across such content to report GridinSoft Anti-Malware Crack v4.1.94 Method: material, at which time a "dedicated team" reviews the information.[]

InFacebook announced that influencers are no longer able to post any vape, tobacco products, and weapons promotions on Facebook and Instagram.[]

Women's bodies

In OctoberInstagram deleted the account of Canadian photographer Petra Collins after she posted a photo of herself in which a very small area of pubic hair was visible above the top of her bikini bottom. Collins claimed that the account deletion was unfounded because it broke none of Instagram's terms and conditions.[] Audra Schroeder of The Daily Dot further wrote that "Instagram's terms of Duplicate Image Finder Quick Update v1.0.03 crack serial keygen state users can't post "pornographic or sexually suggestive photos," but who actually gets to decide that? You can indeed find more sexually suggestive photos on the site than Collins', where women show the side of "femininity" the world is "used to" seeing and accepting."[] Nick Drewe of The Daily Beast wrote a report the same month focusing on hashtags that users are unable to search for, including #sex, #bubblebutt, and #ballsack, despite allowing #faketits, #gunsforsale and #sexytimes, calling the discrepancy "nonsensical and inconsistent".[]

Similar incidents occurred in Januarywhen Instagram deleted Australian fashion agency Sticks and Stones Agency's account because of a photograph including pubic hair sticking out of bikini bottoms,[] and MarchDuplicate Image Finder Quick Update v1.0.03 crack serial keygen, when artist and poet Rupi Kaur's photos of menstrual blood on clothing were removed, prompting a rallying post on her Facebook and Tumblr accounts with the text "We will not be censored", gaining over 11, shares.[]

The incidents have led to a #FreetheNipple campaign, aimed at challenging Instagram's removal of photos displaying women's nipples. Although Instagram has not made many comments on the campaign,[] an October explanation from CEO Kevin Systrom highlighted Apple's content guidelines for apps published through its App Store, including Instagram, in which apps must designate the appropriate age ranking for users, with the app's current rating being 12+ years of age. However, this statement has also been called into question due to other apps with more explicit content allowed on the store, the lack of consequences for men exposing their bodies on Instagram, and for inconsistent treatment of what constitutes inappropriate exposure of the female body.[][]

Censorship by countries

Instagram is the most popular social networking site in Iran(in red), also the only country where this is the case.

Censorship of Instagram has occurred in several different countries.

United States

On October 30,Instagram temporarily removed the "recent" tab on hashtag pages to prevent the spread of misinformation regarding the United States presidential election.[] On January 7,United States PresidentDonald Trump was banned from Instagram "indefinitely". Zuckerberg stated "We believe the risks of allowing the President to continue to use our service during this period are simply too great."[]

China

See also: Internet censorship in China

Instagram has been blocked by China following the Hong Kong protests as many confrontations with police and incidents occurring during the protests were recorded and photographed. Hong Kong and Macau were not affected as they are part of special administrative regions of China.[]

Turkey

Turkey is also known for its strict Internet censorship and periodically blocks social media including Instagram.[]

North Korea

See also: Internet in North Korea

A few days after a fire incident that happened in the Koryo Hotel in North Korea on June 11,authorities began to block Instagram to prevent photos of the incident from being spread out.[]

Iran

Iran has sentenced several citizens to prison for posts made on their Instagram accounts.[] The Iranian government also blocked Instagram periodically during anti-government protests.[] In JulyInstagram temporarily censored videos with the phrase "death to Khamenei".[]

Cuba

The Cuban government blocked access to several social media platforms, including Instagram, to curb the spread of information during the Cuban protests.[]

In popular culture

System

Instagram is written in Python.[]

Instagram AI describes content for visually impaired people that use screen readers.[]

See also

Notes

  1. ^The name is often colloquially abbreviated as IG, Insta, or the Gram.[9]

References

  1. ^"Instagram APKs". APKMirror.
  2. ^"‎Instagram". App Store.
  3. ^"Instagram". Amazon Appstore for Android.
  4. ^ ab"Instagram APKs". APKMirror.
  5. ^"Instagram". App Store. Retrieved May 10,
  6. ^"Instagram APKs". APKMirror. Retrieved May 9,
  7. ^"shoppingdowntown.us: Instagram: Appstore for Android". shoppingdowntown.us.
  8. ^"Instagram". App Store. Retrieved October 7,
  9. ^For example:Edwards, Erica B.; Esposito, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, Jennifer (). "Reading social media intersectionally". Intersectional Analysis as a Method to Analyze Popular Culture: Clarity in the Matrix. Futures of Data Analysis in Qualitative Research. Abingdon: Routledge. ISBN&#. Retrieved May 7,
  10. ^ ab"Instagram Stories is Now Being Used by Million People Daily". Social Media Today. Retrieved April 16,
  11. ^"Instagram hits 1 billion monthly users, up from M in September". TechCrunch. Retrieved October 23,
  12. ^ abMiller, Chance (December 17, ). "These were the most-downloaded apps and games of the decade". 9to5Mac. Retrieved December 17,
  13. ^"An Egg, Just a Regular Egg, Is Instagram's Duplicate Image Finder Quick Update v1.0.03 crack serial keygen Post Ever". The New York Times. Retrieved January 14,
  14. ^"The 20 Most Liked Pictures on Instagram". Brandwatch. Retrieved June 10,
  15. ^ abLagorio, Christine (June 27, ). "Kevin Systrom and Mike Krieger, Founders of Instagram". Inc. Retrieved October 4,
  16. ^Sengupta, Somini; Perlroth, Nicole; Wortham, Jenna (April 13, ). "Behind Instagram's Success, Networking the Old Way". The New York Times. Retrieved April 12,
  17. ^ ab"Take a Look Back at Instagram's First Posts, Six Years Ago". Time. Retrieved February 10,
  18. ^"5 Of The Most Popular Instagram Accounts". Yahoo! Finance. Retrieved February 10,
  19. ^Siegler, MG (March 5, ). "Burbn's Funding Goes Down Smooth. Baseline, Andreessen Back Stealthy Location Startup". TechCrunch. AOL. Retrieved April 12,
  20. ^ abcShontell, Alyson (April 9, ). "Meet Duplicate Image Finder Quick Update v1.0.03 crack serial keygen 13 Lucky Employees And 9 Investors Behind $1 Billion Instagram". Business Insider. Retrieved April 12,
  21. ^Beltrone, Gabriel (July Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, ). "Instagram Surprises With Fifth Employee". Adweek. Beringer Capital. Retrieved April 12,
  22. ^"Instagram post by Mike Krieger • Jul 16, at pm UTC". Instagram. Retrieved February 10, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen,
  23. ^"Instagram post by Kevin Systrom • Jul 16, at pm UTC". Instagram.
  24. ^"Here's The First Instagram Photo Ever". Time.
  25. ^Siegler, MG (October 6, ). "Instagram Launches with the Hope of Igniting Communication Through Images". TechCrunch. AOL. Retrieved April 8,
  26. ^Siegler, MG (February 2, ). "Instagram Filters Through Suitors To Capture $7 Million in Funding Led By Benchmark". TechCrunch. AOL. Retrieved April 22,
  27. ^Markowitz, Eric (April 10, ). "How Instagram Grew From Foursquare Knock-Off to $1 Billion Photo Empire". Inc. Mansueto Ventures, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. Retrieved April 22,
  28. ^Tsotsis, Alexia (April 9, ). "Right Before Acquisition, Instagram Closed $50M at A$M Valuation From Sequoia, Thrive, Greylock And Benchmark". TechCrunch. AOL. Retrieved April 22,
  29. ^"The Year-Old VC Who Cashed In On Instagram". Forbes. Retrieved January 2,
  30. ^ abTsotsis, Alexia (April 3, ). "With Over 30 Million Users on iOS, Instagram Finally Comes To Android", Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. TechCrunch. AOL. Retrieved April 8,
  31. ^Houston, Thomas (April 3, ). "Instagram for Android now available", Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. The Verge. Retrieved April 8,
  32. ^Blagdon, Jeff (April 4, ). "Instagram for Android breaks 1 million downloads in less than a day". The Verge. Retrieved April 22,
  33. ^Bell, Karissa (March 11, ). "Instagram Releases Faster, More Responsive Android App". Mashable. Retrieved April 24,
  34. ^Cohen, David (March 11, ). "Twice As Quick, Half As Large: Instagram Updates Android App". Adweek. Beringer Capital. Retrieved April 24,
  35. ^Constine, Josh (April 18, ). "Instagram on Android gets offline mode". TechCrunch. AOL. Retrieved April 24,
  36. ^O'Kane, Sean (April 19, ). "Instagram for Android now works offline". The Verge. Retrieved April 24,
  37. ^Ghoshal, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, Abhimanyu (April 19, ). "Instagram now works offline on Android". The Next Web. Retrieved April 24,
  38. ^Upbin, Bruce (April 9, ). "Facebook Buys Instagram For $1 Billion. Smart Arbitrage". Forbes. Retrieved April 22,
  39. ^Rusli, Evelyn M. (April 9, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, ). "Facebook Buys Instagram for $1 Billion". The New York Times. Retrieved April 22,
  40. ^Oreskovic, Alexei; Shih, Gerry (April 10, ). "Facebook to buy Instagram for $1&#;billion". Reuters. Retrieved April 22,
  41. ^Constine, Josh; Cutler, Kim-Mai (April 9, ). "Facebook Buys Instagram For $1 Billion, Turns Budding Rival into Its Standalone Photo App". TechCrunch. AOL. Retrieved April 22,
  42. ^Houston, Thomas (April 9, ). "Facebook to buy Instagram for $1&#;billion". The Verge. Retrieved April 22,
  43. ^ ab
Источник: [shoppingdowntown.us]

Natural Resources Conservation Service

SSM - Ch. 3. Examination and Description of Soil Profiles

Revised by Soil Science Division Staff.
 

Quick Links

Introduction
General Terms Used to Describe Soils
Studying Pedons
Designations for Horizons and Layers
Near Surface Subzones
Root-Restricting Depth
Particle-Size Distribution
Soil Texture
Rock Fragments and Pararock Fragments
Artifacts
Compound Texture Modifiers
Fragments on the Surface
Soil Color
Soil Structure
Internal Ped and Void Surface Features
Concentrations
Pedogenic Carbonates
Redoximorphic Features
Consistence
Roots
Pores
Animals
Selected Chemical Properties
Soil Water
Soil Temperature
References
 

Introduction

A description of the soils is essential in any soil survey. This chapter provides standards and guidelines for describing the soil. It contains standard technical terms and their definitions for most soil properties and features and provides information for describing the necessary related facts. For some soils, standard terms are not adequate and must be supplemented by a narrative. Some soil properties change through time. Many properties must be observed over time and summarized if one is to fully understand the soil being described and its response to short-term environmental changes. Examples are the length of time that cracks remain open, the patterns of soil temperature and moisture, and the variations in size, shape, and hardness of clods in the surface layer of tilled soils.

This chapter does not discuss every possible soil property, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. For some soils, other properties need to be described. Good judgment is needed to decide what properties merit detailed attention for any given pedon (sampling unit). Observations must not be limited by preconceived ideas about what is important.

Although the format of the description and the order in which individual properties are described are less important than the content of the description, a standard format has distinct advantages. The reader can find information more rapidly, and the writer is less likely to omit important features. Furthermore, a standard format makes data entry into a computer database more efficient. Any standardized forms need to allow enough space for all possible information.

Each investigation of the internal properties of a soil is made on a soil body with certain dimensions. The body may be larger than a pedon (e.g., a backhoe pit) or represent only a portion of a pedon (e.g., a sample from a hand auger). During field operations, many soils are investigated by examining the soil material removed by a sampling tube or auger. For rapid investigations of thin soils, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, a small pit can be dug and a section of soil removed with a spade. All of these are samples of pedons. Knowledge of the internal properties of a soil is derived mainly from studies of such samples. Samples can be studied more rapidly than entire pedons; consequently, a much larger number can be studied and for several more places. For many soils, the information obtained from a small sample amply describes the pedon from which it is taken. For other soils, however, important properties of a pedon are not observable in a smaller sample and detailed studies of the entire pedon are needed. Complete study of an entire pedon requires the exposure of a vertical section and the removal of horizontal sections layer by layer. Horizons are studied in both horizontal and vertical dimensions. The kind of exposure (e.g., bucket auger, push tube, small hand-dug pit, backhoe pit, road cut, etc.) should be identified in the soil description.

The information in this chapter, which focuses on the standards and guidelines for describing a soil profile in the field, is complemented by that provided in chapters 2, 6, 10, and Chapter 2 provides information related to describing the site Adobe Edge Animate CC 2014 Crack Full Version Download the soil profile. Chapter 6 discusses the use of proximal sensors to measure some soil properties quickly and efficiently at field and larger scales by using field-based electronic technology. Chapter 10 provides information specific to describing subaqueous soils. Chapter 11 discusses soils heavily impacted by human activity.
 

General Terms Used to Describe Soils

This section describes several of the general terms for internal elements of the soil. Other more specific terms are described or defined in the following sections.

Pedon

A pedon is a three-dimensional body of soil that has sufficient area (roughly 1 to 10 m2) and depth (up to cm) to be used in describing the internal arrangement of horizons and in collecting representative samples for laboratory analysis (see chapter 4). The pedon is the individual classified with Soil Taxonomy. Multiple pedons that have the same classification and occur together in landscapes are used in defining soil series. Conceptually, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, these contiguous pedons are called polypedons (see chapter 4).

Soil Profile

A soil profile is smaller than a pedon. It is exposed by a two-dimensional vertical cut through the soil. It is commonly conceived as a plane at right angles to the soil surface. In practice, a description of a soil profile includes soil properties that can be determined only by inspecting volumes of soil, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. However, the volume of soil described from a profile is almost always less than the volume of soil defined by a full pedon because observations of the soil profile are generally made to only a few decimeters behind the face of the exposed profile. A pedon description is commonly based on examination of a profile, and the properties of the pedon are inferred from the properties of the profile. The width of a profile ranges from a few decimeters to several meters or more. The size of the profile should be sufficient to include the largest structural units.

Soil Horizon

A soil horizon is a layer, approximately parallel to the surface of the soil, that is distinguishable from adjacent layers by a distinctive set of properties produced by the soil-forming processes (i.e., pedogenesis). The term “layer” is used instead of “horizon” if the properties are inherited from the parent material, such as sedimentary strata. Horizons, in contrast, display the effects of pedogenesis, such as the obliteration of sedimentary strata and accumulation of illuvial clay.

Solum

The solum (plural, sola) of a soil consists of a set of horizons that are related through the same period of pedogenesis. It includes all horizons now forming. It may also include a bisequum (discussed below). It does not include a buried soil or layer unless it has acquired some of its properties by currently active soil-forming processes. The solum of a soil is not necessarily confined to the zone of major biological activity. Its genetic horizons may be expressed faintly to prominently. A solum does not have a maximum or minimum thickness.

Solum and soils are not synonymous. Some soils include layers that are not affected by soil formation. These layers are not part of the solum. The number of genetic horizons ranges from one to many. An A horizon that is 10 cm thick overlying bedrock is by itself the solum. A soil that consists only of recently deposited new soil material or recently exposed soft sediment generally does not have a solum.

In terms of soil horizons as described in this chapter, a solum consists of O, V, A, E, and B horizons and their transitional horizons. Included are horizons with an accumulation of carbonates or more soluble salts if these horizons are either within, or contiguous to, other genetic horizons and are judged to be at least partly produced during the same period of soil formation.

The lower limit of the solum, in a general sense, in many soils should be related to the depth of rooting for perennial plants, assuming that water state and chemistry are not limiting. In some soils, the lower limit can be set only arbitrarily and is defined in relation to the particular soil. For example, horizons of carbonate accumulation are easily visualized as part of the solum in many soils in arid and semiarid environments. However, to conceive of cemented horizons of carbonates that may extend for 5 meters or more below the surface as part of the modern solum is more difficult. Such massive carbonate horizons represent pedogenesis over hundreds of thousands of years and are referred to as relict paleosols. Gleyed soil material begins in some soils a few centimeters below the surface and continues practically unchanged to a depth of many meters. Gleying immediately below the A horizon is likely to be related to the processes of soil formation in the modern soil. At great depth, gleying is likely to be relict or related to processes that are more geological than pedological. The same kind of problem exists for some deeply weathered soils—the deepest material penetrated by roots is very similar to the weathered material at much greater depth.

For some soils, digging deep enough to reveal all of the relationships between soils and plants is not practical. Plant roots, for example, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen derive much of their moisture from fractured bedrock. Descriptions should indicate the nature of the soil-rock contact and determinations about the upper part of the underlying rock.

Not everyone will agree about the exact extent of the solum in some soils. For example, a certain level of subjectivity is involved in differentiating transitional BC or CB horizons from C horizons or in determining which properties ApowerMirror 1.6.0.3 Full Crack + Activation Code 2021 [Latest] in the soil are the product of active pedogenic processes. The concept of the solum remains useful for discussions about the nature of soils and soil profiles but is generally not used as a part of any technical definitions.

Sequum

A sequum (plural, sequa) consists of a B horizon and any overlying eluvial horizons. A single sequum is considered to be the product of a specific combination of soil-forming processes.

Most soils have only one filmora scrn crack 2019 Archives, but some have two or more. For example, a new sequence of horizons that meet the criteria for a Spodosol can form in the upper part of a previously existing Alfisol, producing an eluviated zone and a spodic horizon underlain by another eluviated zone overlying an argillic horizon. Such a soil has two sequa. Soils in which two sequa have formed, one above the other in the same deposit, are said to be bisequal.

If two sequa formed in different deposits at different times, the soil is not bisequal, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. For example, a soil having an A-E-B horizon sequence may form in material that was deposited over another soil that already had an A-E-B horizon sequence. Each set of A-E-B horizons is a sequum, but the combination is not a bisequum; the lower set is a buried soil. If the horizons of the upper sequum extend into the underlying sequum, the affected layer is considered part of the upper sequum. For example, the A horizon of the lower soil may retain some of its original characteristics and also have some Wise Care 365 Pro 5.7.1 Build 571 +Crack With Key Free Full latest 2021 of the overlying soil. In this case, the soils are also not considered bisequal; the upper part of the lower soil is the parent material of the lower part of the currently forming soil. In many soils the distinction cannot be made with certainty. If some of the C material of the upper sequum remains, the distinction is clear.
 

Studying Pedons

Site Selection

Pedons representative of an extensive mappable area are generally more useful than pedons that represent a transitional area to another soil. For detailed study of a soil, a pedon is tentatively selected and then examined preliminarily to determine whether or not it represents the desired segment of the soil’s range. This is a critical step. Typically, only a few pedons can be studied in detail due to the time and expense involved in exposing, describing, photographing, and sampling soil profiles and performing necessary laboratory analysis. It is very important that the site selected for study is a representative sample of the overall soil body in the landscape because data from the site will be used to classify the soil pedon and correlate it with other similar pedons.

Information Recorded

For a soil description to be of greatest value, detailed information about its setting should be recorded (see chapter 2). Important items include location (identified by latitude and longitude, including datum, or another acceptable geographic location system), the part of the landscape that the pedon represents (i.e., landform, position on landform, any applicable microfeature), elevation, aspect, parent material, vegetation, land use, and erosion or other disturbance affecting the soil profile. The level of detail will depend on the objectives. A complete setting description should include information about the pedon and other soils conterminous with the pedon. It also may include information on any features that differ from the central concept of the soil series for which the described pedon is named (if a series has been defined).

The description of a body of soil in the field, whether an entire pedon or a soil profile within it, should record the kinds of horizons or layers, their depth and thickness, and the properties of each. Generally, external features, such as slope, surface stoniness, erosion, and vegetation, are observed for the area around the pedon, which is considered to be part of the same soil body. Internal features, such as color, texture, and structure, are observed from the study of the pedon.

Observing Pedons

In order to observe a pedon fully, including soil structure (size and kind), horizon boundary topography, and short-range variability in horizon thickness, a pit exposing a vertical face approximately 1 meter across to an appropriate depth (fig. ) is adequate for most soils. Excavations associated with roads, railways, gravel pits, and other soil disturbances provide easy access for studying soils. Old exposures, however, must be used cautiously. In these areas, the soils can dry out or freeze and thaw from both the surface and the sides. In addition, the soil structure may be more pronounced than is typical, salts may have accumulated near the edges of exposures or been removed by seepage, plinthite may have irreversibly hardened to ironstone, or other changes may have taken place.

Figure A shallow soil pit with a face that has been cleaned and prepared for describing the soil profile. This soil (a Fibristel in Alaska) has been dug to the depth of permafrost (about 40 cm).For hand- or backhoe-dug pits, care must be taken to ensure that the pit conforms to safety regulations. Loose sandy soils and wet soils are particularly susceptible to cave-ins.

After the sides of the pit are cleaned of all loose material disturbed by digging, the exposed vertical faces are examined, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, typically starting at the top and working downward, to identify significant changes in properties. Boundaries between layers are marked on the face of the pit, and the layers are identified and described.

Photographs should be taken after the layers have been identified but before the vertical section is disturbed in the description-writing process. An estimation of the volume of stones or other features also is done before the layers are disturbed.

If bulk samples are to be collected for laboratory analysis, it generally is best to begin with the bottom layer and work upward. This prevents material from the upper layers falling onto the face of lower layers before they have been sampled.

A horizontal view of each horizon is useful. This exposes structural units that otherwise may not be readily observable from the vertical pit face. Patterns of color within structural units, variations of particle size from the outside to the inside of structural units, and the pattern in which roots penetrate structural units are commonly seen more clearly in a horizontal section (fig. ).

Figure A horizontal view (looking down) of a fragipan from a soil (a Fragiudalf) in Tennessee.

Measuring Depth to and Thickness of Horizons and Layers

Soil Surface

When describing soil profiles, depth is measured from the soil surface. Generally, the soil surface is the top of the mineral soil. For soils with an O horizon (Oi, Oe, or Oa), it is the top of the O horizon. Fresh leaf or needle fall that has not undergone observable decomposition is excluded from the concept of an O horizon and may be described separately as a surface feature. Profile measurements begin below any fresh leaf or needle fall.

For soils that have a cover of Duplicate Image Finder Quick Update v1.0.03 crack serial keygen percent or more rock or pararock fragments (as in some areas of rubbly colluvial materials), the top of the soil is considered the mean height of the tops of the rock or pararock fragments. Depth measurements are taken from this height.

It is important to note that, when measuring depth and thickness for taxonomic purposes, the “mineral soil surface” is commonly specified as the datum to use in measurements. This essentially excludes any overlying O horizon and is therefore not synonymous with the soil surface as defined here for making soil descriptions. See Keys to Soil Taxonomy (Soil Survey Staff, b or later version) for further information.

Depth Measurements

The depth to a horizon or layer boundary commonly differs within short distances, even within a pedon. The part of the pedon that is typical or most common is described. In the soil description, the horizon or layer designation is listed, followed by the values that represent the depths from the soil surface to the upper and lower boundaries (e.g., Bt1 - 8 to 20 cm). The depth to the lower boundary of a horizon or layer is the depth to the upper boundary of the horizon or layer beneath it. Variation in the depths of the boundaries is recorded in the description of the horizon or layer. The depth limits of the deepest horizon or layer described include only that part actually seen.

In some soils, the variations in depths to boundaries are so complex that the usual terms used to describe the boundary topography are inadequate. These variations are described separately, e.g., “depth to the lower boundary is mainly 30 to 40 cm, but tongues extend to depths of 60 to 80 cm.” The lower boundary of a horizon or layer and the upper boundary of the horizon or layer below share a common irregularity.

Thickness Measurements

The thickness of each horizon or layer is the vertical distance between the upper and lower boundaries. Overall thickness may vary within a pedon, and this variation should be noted in the description. A range in thickness may be given, e.g., “thickness ranges from 20 to 30 cm.” This range is not calculated from the range of upper and lower boundary depths. Instead, the range is calculated from evaluations across the exposure at different lateral points. For example, the upper boundary of a horizon may range in depth from 25 to 45 cm and the lower boundary from 50 to 75 cm. Taking the extremes of these two ranges, it is incorrect to conclude that the horizon thickness ranges from as little as 5 cm to as much as 50 cm when in fact it may be 20 to 30 cm in the field.
 

Designations for Horizons and Layers

Soils vary widely in the degree to which horizons are expressed. Relatively fresh parent materials, such as recent deposits of alluvium, eolian sands, or mantles of volcanic ash, may have no recognizable genetic horizons but may have distinct layers that reflect different modes of deposition. As soil formation proceeds, horizons in their early stages may be detected only by very careful examination. As horizons increase in age, they generally are more easily identified in the field. However, only one or two different horizons may be readily apparent in some very old, deeply weathered soils in tropical areas where annual precipitation is high. This section provides the standard nomenclature and definitions for a system used to assign symbols to soil horizons and layers.

Background and Concepts for Use of Designations

Different kinds of layers are identified by different symbols. Designations are provided for layers that have been changed by soil formation and for those that have not. Each horizon designation indicates either that the original material has been changed in certain ways or that there has been little or no change. The designation is assigned after comparison of the observed properties of the layer with properties inferred for the material before it was affected by soil formation. The processes that have caused the change need not be known; properties of soils relative to those of an estimated parent material are the criteria for judgment. The parent material inferred for the horizon in question, not the material below the solum, is used as the basis of comparison. The inferred parent material commonly is very similar to, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, or the same as, the soil material below the solum.

Designations show the describer’s interpretations of genetic relationships among the layers within a soil. Layers do not need to be identified by symbols in order to make a good description, but the usefulness of soil descriptions is greatly enhanced by the proper use of designations. The designations provide a sort of shorthand nomenclature conveying the important properties observed by the person describing the soil as well as the genetic inferences made by that person regarding the formation of the soil. The definitions of the symbols provided below are generally more qualitative than quantitative. There is a small degree of subjectivity that allows some freedom for the describer to convey their theory of how the soil formed. There may be a certain level of inconsistency in the way different describers label the horizons of the same profile. For example, one describer may label a horizon “C” while another may label it “CB” or one may record a subtle lithologic discontinuity that another person does not observe.

Designations are not substitutes for descriptions. If both designations and adequate descriptions of a soil are provided, the reader has the interpretation made by the person who described the soil and also the evidence on which the interpretation was based.

Genetic horizons are not equivalent to the diagnostic horizons of Soil Taxonomy. Designations of genetic horizons express a qualitative judgment about the kind of changes that are believed to have taken place. Diagnostic horizons are quantitatively defined features used to differentiate taxa. Changes implied by genetic horizon designations may not be large enough to justify recognition of diagnostic criteria. For example, the designation “Bt” does not always indicate an argillic horizon. Furthermore, the diagnostic horizons may not be coextensive with genetic horizons.

Basic System of Horizon and Layer Designations

Four kinds of symbols are used in various combinations to designate horizons and layers:

Capital letters.—Used to designate the master horizons and layers.
Lowercase letters.—Used as suffixes to indicate specific characteristics of master horizons and layers.
Numbers.—Used both as suffixes to indicate vertical subdivisions within a horizon or layer and as prefixes to indicate discontinuities.
Special symbols.—Used to indicate layers formed in human-transported material or sequences of horizons having otherwise identical designations.

Master Horizons and Layers

The capital letters O, L, V, A, E, B, C, R, M, and W represent the master horizons and layers of soils. These letters are the base symbols to which other characters are added to complete the designations. Most horizons and layers have a designation using one capital letter symbol; some have two.

O Horizons or Layers

O horizons or layers are dominated by organic soil materials. Some are saturated with water for long periods; some were once saturated but are now artificially drained; and others have never been saturated.

Some O horizons or layers consist of slightly decomposed to highly decomposed litter (such as leaves, needles, twigs, moss, and lichens) that was deposited on the surface of either mineral or organic soils. Others consist of organic materials that were deposited under saturated conditions and have decomposed to varying stages. The mineral fraction of Proshow Gold 9.0.3797 torrent Archives material constitutes only a small percentage of the volume of the material and generally much less than half of its weight. Some soils consist entirely of materials designated as O horizons or layers.

An O horizon or layer may be at the surface of a mineral soil or, if buried, at any depth below the surface. A horizon formed by illuviation of organic material into a mineral subsoil is not an O horizon, although some horizons that formed in this manner contain a large amount of organic matter. Horizons or layers composed of limnic materials are not designated as O horizons.

L Horizons or Layers

L horizons or layers include both organic and mineral limnic materials that were either:

  1. Deposited in water by precipitation or through the actions of aquatic organisms, such as algae and diatoms; or
  2. Derived from underwater and floating aquatic plants and subsequently modified by aquatic animals.

L horizons or layers include coprogenous earth (sedimentary peat), diatomaceous earth, and marl. They are described only for Histosols (decomposed plant material) and not for mineral soils. They have only the following suffixes: co, di, or ma (described below), Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. They do not have the subordinate distinctions of the other master horizons and layers.

V Horizons

V horizons are mineral horizons that formed at the soil surface or below a layer of rock fragments (e.g., desert pavement), a physical or biological crust, or recently deposited eolian material. They are characterized by the predominance of vesicular pores and have platy, prismatic, or columnar structure.

Porosity in a V horizon may include vughs and collapsed vesicles in addition to the spherical vesicular pores. V horizons formed in eolian material but may be underlain by soil horizons that formed in residuum, alluvium, or other transported materials. Because of their eolian origin, they are typically enriched in particle-size fractions ranging from silt through fine sand. Rarely, the V horizon is massive rather than structured, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. The structural arrangement of particles and vesicular porosity differentiates this horizon from the loose, unaltered eolian deposits that may occur above it. Underlying B horizons commonly have redder hues than the V horizon and lack vesicular pores (Turk et al., ).

Transitional and combination horizons with V horizon material occur in certain circumstances. Although uncommon, an AV or VA horizon may occur. It is both enriched in organic matter and contains vesicular pores. BV or VB horizons may indicate vesicular horizons that contain clay or carbonate coatings, or other properties of the underlying B horizon. EV or VE transitional horizons may also occur, especially in sodic soils.

Combination horizons of the V horizon with A, B, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, or E horizons may occur in bioturbated zones, such as shrub islands or areas where surface cover associated with the vesicular horizon (e.g., desert pavement) is patchy. Vesicular pores have been observed to reform quickly after physical disruption (Yonovitz and Drohan, ).

A Horizons

A horizons are mineral horizons that formed at the soil surface or below an O horizon. They exhibit obliteration of all or much of any original rock structure and show one or both of the following:

  1. An accumulation of humified organic matter closely mixed with the mineral fraction and not dominated by properties characteristic of V, E, or B horizons; and/or
  2. Properties resulting from cultivation, pasturing, or similar kinds of disturbance.

If a surface horizon has properties of both A and E horizons but the feature emphasized is an accumulation of humified organic matter, it is designated as an A horizon. Recent alluvial or eolian deposits that retain most of the original rock structure are not considered to be A horizons unless they are cultivated.

E Horizons

E horizons are mineral horizons in which the main feature is the eluvial loss of silicate clay, iron, aluminum, or some combination of these that leaves a concentration of sand and silt particles. They exhibit obliteration of all or much of the original rock structure.

An E horizon is commonly differentiated from an underlying B horizon in the same sequum by a color of higher value or lower chroma (or both), by coarser texture, or by a combination of these properties, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. In some soils the color of the E horizon is that of the sand and silt particles, but in many soils coatings of iron oxides or other compounds mask the color of the primary particles. An E horizon is most commonly differentiated from an overlying A horizon by its lighter color. It generally contains less organic matter than the A horizon. It is commonly near the soil surface, below an O, V, or A horizon, and above a B horizon. However, the symbol E can be used for eluvial horizons that are at the soil surface, are within or between parts of the B horizon, or extend to depths greater than those of normal observation, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, if the horizons have resulted from pedogenic processes.

B Horizons

B horizons are mineral horizons that typically formed Duplicate Image Finder Quick Update v1.0.03 crack serial keygen an A, V, E, or O horizon. They exhibit obliteration of all or much of the original rock structure and show one or more of the following as evidence of pedogenesis:

  1. Illuvial concentration of silicate clay, iron, aluminum, humus, sesquioxides, carbonates, gypsum, salts more soluble than gypsum, or silica, alone or in combination;
  2. Evidence of the removal, addition, or transformation of carbonates, anhydrite, and/or gypsum;
  3. Residual concentration of oxides, sesquioxides, and silicate clay, alone or in combination;
  4. Coatings of sesquioxides that make the horizon color conspicuously lower in value, higher in chroma, or redder in hue than overlying and underlying horizons, without apparent illuviation of iron;
  5. Alteration that forms silicate clay or liberates oxides, or both, and that forms pedogenic structure if volume changes accompany changes in moisture content;
  6. Brittleness; or
  7. Strong gleying when accompanied by other evidence of pedogenic change.

All of the different kinds of B horizons are, or originally were, subsurface horizons. B horizons include horizons (cemented or not cemented) with illuvial concentrations of carbonates, gypsum, or silica that are the result of pedogenic processes. They are contiguous to other genetic horizons and brittle layers that show other evidence of alteration, such as prismatic structure or illuvial accumulation of clay.

B horizons do not include layers in which clay films coat rock fragments or cover finely stratified unconsolidated sediments, regardless of whether the films formed in place or by illuviation; layers into which carbonates have been illuviated but that are not contiguous to an overlying genetic horizon; and layers with strong gleying but no other pedogenic changes.

C Horizons or Layers

C horizons or layers are mineral horizons or layers, excluding strongly cemented and harder bedrock, that are little affected by pedogenic processes and lack properties of O, A, V, E, B, and L horizons. Their material may be either like or unlike that from which the solum presumably formed. The C horizon may have been modified, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, even if there is no evidence of pedogenesis.

Included as C layers (and typically designated Cr) are sediment, saprolite, bedrock, and other geologic materials that are moderately cemented or less cemented (see table ). The excavation difficulty of these materials commonly is low or moderate (see table ). In descriptions of soils that formed in material that is already highly weathered, if this material does not meet the requirements of an A, V, E, or B horizon, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, it is designated by the letter C. Changes are not considered pedogenic if they are not related to the overlying horizons. Some layers that have accumulations of silica, carbonates, gypsum, or more soluble salts are included in C horizons, even if cemented. However, if a cemented layer formed through pedogenic processes, rather than geologic processes (e.g., lithification), Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, it is considered a B horizon.

R Layers

R layers consist of strongly cemented to indurated bedrock. Granite, basalt, quartzite, limestone, and sandstone are examples of bedrock that commonly is cemented enough to be designated by the letter R. The excavation difficulty of these layers commonly exceeds high. The R layer is sufficiently coherent when moist to make hand-digging with a spade impractical, although it may be chipped or scraped. Some R layers can be ripped with heavy power equipment. The Duplicate Image Finder Quick Update v1.0.03 crack serial keygen may have fractures, but these are generally too few or too widely spaced to allow root penetration. The fractures may be coated or filled with clay or other material.

M Layers

M layers are root-limiting layers beneath the soil surface consisting of nearly continuous, horizontally oriented, human-manufactured materials. Examples of materials designated by the letter M include geotextile liners, asphalt, concrete, rubber, and plastic, if they occur as continuous, horizontal layers.

W Layers

W layers are used to identify water layers within or beneath the soil (fig. ). They are not merely layers of saturated soil material but rather zones of water between soil layers. The water layer is designated “Wf ” if it is permanently frozen (as in a glacic horizon) and “W” if it is not permanently frozen (as in a floating bog). The designations W and Wf are not used for shallow water, ice, or snow above the Duplicate Image Finder Quick Update v1.0.03 crack serial keygen surface.

Figure A soil (a Glacistel in Alaska) with a <a href=Jogos de Rogue-lite de Graça para Baixar frozen ice layer (designated “Wf”) between depths of 60 and cm. (Photo courtesy of John Kelley)" src="shoppingdowntown.us">

Transitional and Combination Horizons

In some cases a single master horizon designation does not adequately convey information about the layer, such as where the horizon transitions to another layer or where it contains distinct parts from two kinds of master horizons.

Transitional Horizons

Transitional horizons are dominated Duplicate Image Finder Quick Update v1.0.03 crack serial keygen properties of one master horizon but have subordinate properties of another. They are designated by two capital-letter symbols, e.g., AB, EB, BE, or BC. The first letter indicates the horizon whose properties dominate the transitional horizon. An AB horizon, for example, has characteristics of both an overlying A horizon and an underlying B horizon, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, but it is more like the A horizon than the B.

In some cases, a horizon can be designated as transitional even if one of the master horizons to which it transitions is not present. For example, a BE horizon recognized in a truncated soil has properties similar to those of a BE horizon in a soil from which the overlying E horizon has not been removed by erosion. A BC horizon may be recognized even if no underlying C horizon is present: it transitions to assumed parent materials.

Combination Horizons

Combination horizons have two distinct parts that have recognizable properties of the two kinds of master horizons. They are designated by two capital-letter symbols (master horizons) separated by a virgule (/), e.g., E/B, B/E, or B/C. Most of the individual parts of one horizon component are surrounded by the other. The designation may be used even when horizons similar to one or both of the components are not present, provided that the separate components can be recognized in the combination horizon. The first letter indicates the horizon with the greater volume.

Because single sets of designators do not cover all situations, some improvising may be necessary. For example, Lamellic Udipsamments have lamellae that are separated from each other by eluvial layers. It is generally not practical to describe each lamella and eluvial layer as a separate horizon, so the horizons can be combined and the components described separately. The horizon with several lamellae and eluvial layers can be designated as an “E and Bt” horizon. The complete horizon sequence for these soils could be: Ap-Bw-E and Bt1-E and Bt2-C.

Suffix Symbols

Lowercase letters are used as suffixes to designate specific subordinate distinctions within master horizons and layers. The term “accumulation,” which is used in many of the suffix definitions, indicates that the horizon has more of the material in question than is presumed to have been present in the parent material. The use of a suffix symbol is not restricted only to those horizons that meet certain criteria for diagnostic horizons and other criteria as defined in Soil Taxonomy. If there is any evidence of accumulation, a suffix (or suffixes) can be used. The suffix symbols and their meanings follow:

aHighly decomposed organic material

This symbol is used with O horizons to indicate the most highly decomposed organic materials, which have a fiber content of less than 17 percent (by volume) after rubbing.

bBuried genetic horizon

This symbol indicates identifiable buried horizons with major genetic features that developed before burial. Genetic horizons may or may not have formed in the overlying material, which may be either like or unlike the assumed parent material of the buried horizon. This symbol is not used to separate horizons composed of organic soil material (that are forming at the soil surface) from underlying horizons composed of mineral soil material. It may be used in organic soils, but only if they are buried by mineral soil materials.

cConcretions or nodules

This symbol indicates a significant accumulation of concretions or nodules. Cementation is required. The cementing agent commonly is iron, aluminum, manganese, or titanium. It cannot be silica, dolomite, calcite, gypsum, anhydrite, or soluble salts.

coCoprogenous earth

This symbol, used only with L horizons, indicates a limnic layer of coprogenous earth (sedimentary peat).

dPhysical root restriction

This symbol indicates non-cemented, root-restricting layers in naturally occurring or human-made sediments or materials. Examples of natural layers are dense till and some non-cemented shales and siltstones. Examples of human-made dense layers are plowpans and mechanically compacted zones in human-transported material.

diDiatomaceous earth

This symbol, used only with L horizons, indicates a limnic layer of diatomaceous earth.

eOrganic material of intermediate decomposition

This symbol is used with O horizons to indicate organic materials of intermediate decomposition. The fiber content of these materials is 17 to less than 40 percent (by volume) after rubbing.

fFrozen soil or water

This symbol indicates that a horizon or layer contains permanent ice. It is not used for seasonally frozen layers or for dry permafrost.

ffDry permafrost

This symbol indicates a horizon or layer that is continually colder than 0 °C and does not contain enough ice to be cemented by ice. It is not used for horizons or layers that have a temperature warmer than 0 °C at some time during the year.

gStrong gleying

This symbol indicates either that iron has been reduced and removed during soil formation or that saturation with stagnant water has preserved iron in a reduced state. Most FL Studio 12 Crack Registration Key Download [Latest] Version 2021 the affected layers have chroma of 2 or less, and many have redox concentrations, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. The low chroma can represent either the color of reduced iron or the color of the uncoated sand and silt particles from which iron has been removed. The symbol is not used for soil materials of low chroma that have no history of wetness, such as some shales or E horizons. If it is used with B horizons, pedogenic change (e.g., soil structure) in addition to gleying is implied. If no other pedogenic change besides gleying has taken place, the horizon is designated “Cg.”

hIlluvial accumulation of organic matter

This symbol is used with B horizons to indicate the accumulation of illuvial, amorphous, dispersible complexes of organic matter and sesquioxides. The sesquioxide component is dominated by aluminum and is present only in very small Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. The organo-sesquioxide material coats sand and silt particles. In some horizons these coatings have coalesced, filled pores, and cemented the horizon. The symbol h is also used in combination with the symbol s (e.g., Bhs) if the amount of the sesquioxide component is significant but the value and chroma, moist, of the horizon are 3 or less.

iSlightly decomposed organic material

This symbol is used with O horizons to indicate the least decomposed of the organic materials. The fiber content of these materials is 40 percent or more (by volume) after rubbing.

jAccumulation of jarosite

This symbol indicates an accumulation of jarosite, which is a potassium (ferric) iron hydroxy sulfate mineral, KFe3(SO4)2(OH)6. Jarosite is commonly the product of pyrite that has been exposed to an oxidizing environment. It has hue of Y or yellower and normally has chroma of 6 or more, although chroma as low as 3 or 4 has been reported. It forms in preference to iron (hydr)oxides in active acid sulfate soils at pH of or less and can be stable for long periods of time in post-active acid sulfate soils with higher pH.

jjEvidence of cryoturbation

This symbol indicates evidence of cryoturbation, which includes irregular and broken horizon boundaries, sorted rock fragments, and organic soil materials occurring as bodies and broken layers within and/or between mineral soil layers. The organic bodies and layers are most commonly at the contact between an active layer and the permafrost.

kAccumulation of secondary carbonates

This symbol indicates an accumulation of visible pedogenic calcium carbonate (less than 50 percent, by volume). Carbonate accumulations occur as carbonate filaments, coatings, masses, nodules, disseminated carbonate, or other forms.

kkEngulfment of horizon by secondary carbonates

This symbol indicates major accumulations of pedogenic calcium carbonate. It is used when the soil fabric is plugged with fine grained pedogenic carbonate (50 percent or more, by volume) that occurs as an essentially continuous medium. It corresponds to the Stage III (or higher) plugged horizon of the carbonate morphogenetic stages (Gile et al., ).

mPedogenic cementation

This symbol indicates continuous or nearly continuous pedogenic cementation. It is used only for horizons that are more than 90 percent cemented but may be fractured. The cemented layer is physically root-restrictive. The predominant cementing agent (or the two dominant ones) can be indicated by letter suffixes, singly or in pairs. The horizon suffix kkm (and the less commonly used km) indicates cementation by carbonates; qm, cementation by silica; sm, cementation by iron; yym, cementation by gypsum; kqm, cementation by carbonates and silica; and zm, cementation by salts more soluble than gypsum. The symbol m is not used for permanently frozen layers impregnated by ice.

maMarl

This symbol, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, used only with L horizons, indicates a limnic layer of marl.

nAccumulation of sodium

This symbol indicates an accumulation of exchangeable sodium.

oResidual accumulation of sesquioxides

This symbol indicates a residual accumulation of sesquioxides.

pTillage or other disturbance

This symbol indicates disturbance of a horizon by mechanical means, pasturing, or similar uses. A disturbed organic horizon is designated “Op.” A disturbed mineral horizon is designated “Ap” even if it is clearly a former E, B, or C horizon.

qAccumulation of silica

This symbol indicates an accumulation of secondary silica.

rWeathered or soft bedrock

This symbol is used with C horizons to indicate layers of bedrock that are moderately cemented or less cemented. Examples are weathered igneous rock and partly consolidated sandstone, siltstone, or shale. The excavation difficulty is low to high.

sIlluvial accumulation of sesquioxides and organic matter

This symbol is used with B horizons to indicate an accumulation of illuvial, amorphous, dispersible complexes of organic matter and sesquioxides, if both the organic matter and sesquioxide components are significant and if either the value or chroma, moist, of the horizon is 4 or more. The symbol is also used in combination with h (e.g., Bhs) if both the organic matter and sesquioxide components are significant and if the value and chroma, moist, are 3 or less.

sePresence of sulfides

This symbol indicates the presence of sulfides in mineral or organic horizons. Horizons with sulfides typically have dark colors (e.g., value Traktor Pro 3 Crack Method: 4 or less, chroma of 2 or less). These horizons typically form in soils associated with coastal environments that are permanently saturated or submerged (i.e., tidal marshes or estuaries). Soil materials which have sulfidization actively occurring emanate hydrogen sulfide gas, which is detectable by its odor (Fanning and Fanning, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, ; Fanning et al., ). Sulfides may also occur in upland environments that have a source of sulfur. Soils in such environments are commonly of geologic origin and may not have a hydrogen sulfide odor. Examples include soils that formed in parent materials derived from coal deposits, such as lignite, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, or soils that formed in coastal plain deposits, such as glauconite, that have not been oxidized because of thick layers of overburden.

ssPresence of slickensides

This symbol indicates the presence of pedogenic slickensides. Slickensides result directly from the swelling of clay minerals and shear failure, commonly at angles of 20 to 60 degrees above horizontal. They are indicators that other vertic characteristics, such as wedge-shaped peds and surface cracks, may be present.

tAccumulation of silicate clay

This symbol indicates an accumulation of silicate clay that either has formed within a horizon and subsequently has been translocated within the horizon or that has been moved into the horizon by illuviation, or both. At least some part of the horizon shows evidence of clay accumulation, either as coatings on surfaces of peds or in pores, as lamellae, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, or as bridges between mineral grains.

uPresence of human-manufactured materials (artifacts)

This symbol indicates the presence of objects or materials that have been created or modified by humans, typically for a practical purpose in habitation, manufacturing, excavation, or construction activities. Examples of artifacts are bitumen (asphalt), boiler slag, bottom ash, brick, cardboard, carpet, cloth, coal combustion by-products, concrete (detached pieces), debitage (i.e., stone tool flakes), fly ash, glass, metal, paper, plasterboard, plastic, potsherd, rubber, treated wood, and untreated wood products.

vPlinthite

This symbol is used to indicate the presence of iron-rich, humus-poor, reddish material Duplicate Image Finder Quick Update v1.0.03 crack serial keygen is firm or very firm when moist and is less than strongly cemented. Plinthite hardens irreversibly when exposed to the atmosphere and to repeated wetting and drying.

wDevelopment of color or structure

This symbol is used only with B horizons to indicate the development of color or structure, or both, with little or no apparent illuvial accumulation of material. Note: It is not used to indicate a transitional horizon.

xFragipan character

This symbol indicates a genetically developed layer that has a combination of firmness and brittleness and commonly a higher bulk density than adjacent layers. Some part of the layer is physically root-restrictive.

yAccumulation of gypsum

This symbol indicates an accumulation of gypsum. It is used when the horizon fabric is dominated by soil particles or minerals other than gypsum. Gypsum is present in amounts that do not significantly obscure or disrupt other features of the horizon. This symbol is also used to indicate the presence of anhydrite.

yyDominance of horizon by gypsum

This Duplicate Image Finder Quick Update v1.0.03 crack serial keygen indicates a horizon that is dominated by the presence of gypsum. The gypsum content may be due to an accumulation of secondary gypsum, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, the transformation of primary gypsum inherited from parent material, or other processes. This symbol is used when the horizon fabric has such an abundance of gypsum (generally 50 percent or more, by volume) that pedogenic and/or lithologic features are obscured or disrupted by growth of gypsum crystals. Horizons that have this suffix typically are highly whitened (e.g., value of 7 through and chroma of 4 or less). This symbol is also used to connote the presence of anhydrite.

zAccumulation of salts more soluble than gypsum

This symbol indicates an accumulation of salts that are more soluble than gypsum.

Conventions for Using Horizon Designation Symbols

The following guidelines can be used in assigning horizon designation symbols to soil horizons and layers.

Letter Suffixes

Many master horizons and layers that are symbolized by a single capital letter can have one or more lowercase-letter suffixes. The following rules apply:

  1. Letter suffixes directly follow the capital letter of the master horizon or layer, or the prime symbol, if used.
  2. More than three suffixes are rarely used.
  3. If more than one suffix is needed, the following letters (if used) are written first: a, d, e, h, i, r, s, t, and w. None of these letters are used in combination for a single horizon, except to designate a Bhs horizon or Crt layer.
  4. If more than one suffix is needed and the horizon is not buried, the following symbols, if used, are written last: c, f, g, m, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, v, and x. Examples are Bjc and Bkkm. If any of these suffixes are used together in the same horizon, symbols c and g are written last (e.g., Btvg), with one exception. If the symbol f (frozen soil or water) is used together with any of the other symbols in this rule, it is written last, e.g., Cdgf.
  5. If a genetic horizon is buried, the suffix b is written last, e.g., Oab.
  6. Suffix symbols h, s, and w are not used with g, k, kk, n, o, q, y, yy, or z.
  7. If the above rules do not apply to certain suffixes, such as k, kk, q, y, or yy, the suffixes may be listed together in order of assumed dominance or alphabetically if dominance is not a concern.

A B horizon that has a significant accumulation of clay and also shows development of color or structure, or both, is designated “Bt” (suffix symbol t has precedence over symbols w, s, and h). A B horizon that is gleyed or that has accumulations of carbonates, sodium, silica, gypsum, salts more soluble than gypsum, or residual accumulations of sesquioxides carries the appropriate symbol: g, k, kk, n, q, y, yy, z, or o. If illuvial clay is also present, the symbol t precedes the other symbol, e.g., Bto.

Vertical Subdivisions

Commonly, a horizon or layer designated by a single letter or a combination of letters has to be subdivided. For this purpose, numbers are added to the letters of the horizon designation. These numbers follow all the letters. Within a sequence of C horizons, for example, successive layers may be designated C1, C2, C3, etc. If the lower horizons are strongly gleyed and the upper horizons are not strongly gleyed, they may be designated C1-C2-Cg1-Cg2 or C-Cg1-Cg2-R.

These conventions apply regardless of the purpose of the subdivision. In many soils a horizon that could be identified by a single set of letters is subdivided to recognize differences in morphological features, such as structure, color, or texture. These divisions are numbered consecutively, but the numbering starts again at 1 when any letter of the horizon symbol changes, e.g., Bt1-Bt2-Btk1-Btk2 (not Bt1-Bt2-Btk3-Btk4). The numbering of vertical subdivisions within consecutive horizons is not interrupted at a discontinuity (indicated by a numerical prefix) if the same letter combination is used in both materials, e.g., Bs1-BsBsBs4 (not Bs1-BsBsBs2).

During sampling for laboratory analyses, thick soil horizons are sometimes subdivided even though differences in morphology are not evident in the field. These subdivisions are identified by numbers that follow the respective horizon designations. For example, four subdivisions of a Bt horizon sampled by cm increments are designated Bt1, Development Archives, Bt3, and Bt4. If the horizon has already been subdivided because of differences in morphological features, the set of numbers that identifies the additional sampling subdivisions follows the first number. For example, three subdivisions of a Bt2 horizon sampled by cm increments are designated Bt21, Bt22, and Bt The descriptions for each of these sampling subdivisions can be the same, and a statement indicating that the horizon has been subdivided only for sampling purposes can be added.

Discontinuities

Numbers are used as prefixes to horizon designations (specifically, A, V, E, B, C, and R) to indicate discontinuities in mineral soils. These prefixes are distinct from the numbers that are used as suffixes denoting vertical subdivisions.

A discontinuity that can be identified by a number prefix is a significant change in particle-size distribution or mineralogy that indicates a difference in the parent material from which the horizons have formed and/or a significant difference in age, unless the difference in age is indicated by the suffix b. Symbols that identify discontinuities are used only when they can contribute substantially to an understanding of the relationships among horizons. The stratification common to soils that formed in alluvium is not designated as a discontinuity, unless particle-size distribution differs markedly from layer to layer (i.e., particle-size classes are strongly contrasting) even though genetic horizons may have formed in the contrasting layers.

If a soil formed entirely in one kind of material, the whole profile is understood to be material 1 and the number prefix is omitted from the symbol. Similarly, the uppermost material in a profile consisting of two or more contrasting materials is understood to be material 1 and the number is omitted. Numbering starts with the second layer of contrasting material, which is designated 2. Underlying contrasting layers are numbered consecutively. Even when the material of a layer below material 2 is similar to material 1, it is designated 3 in the sequence; the numbers indicate a change in materials, not types of material. Where two or more consecutive horizons have formed in the same kind of material, the same prefix number indicating the discontinuity is applied to all the designations of horizons in that material, for example, Ap-E-BtBtBtBC. The suffix numbers designating vertical subdivisions of the Bt horizon continue in consecutive order across the discontinuity. However, vertical subdivisions do not continue across lithologic discontinuities if the horizons are not consecutive or contiguous to each other. If other horizons intervene, another vertical numbering sequence begins for the lower horizons, for example, A-C1-CBwBwCC2.

If an R layer is below a soil that formed in residuum and if it is similar to the material from which the soil developed, the number prefix is not used. The Duplicate Image Finder Quick Update v1.0.03 crack serial keygen is used, however, if it is thought that the R layer would weather to material unlike that in the solum, e.g., A-Bt-C-2R or A-Bt-2R. If part of the solum has formed in residuum, the symbol R is given the appropriate prefix, for example, Ap-BtBtBtCCR.

A buried genetic horizon (designated by the suffix b) requires special consideration. It is obviously not in the same deposit as the overlying horizons. Some buried horizons, however, formed in material that is lithologically like the overlying deposit. In this case, a prefix is not used to distinguish material of the buried horizon. If the material in which a horizon of a buried soil formed is lithologically unlike the overlying material, the discontinuity is indicated by a number prefix and the symbol for the buried horizon also is used, for example, Ap-Bt1-Bt2-BC-C-2ABb-2BtbBtbC.

Discontinuities between different kinds of layers in organic soils are not identified. In most cases, such differences are identified by letter suffixes if the different layers are organic materials (e.g., Oe vs. Oa) or by the master horizon symbol if the different layers are mineral or limnic materials (e.g., Oa vs. Ldi).

The Prime Symbol

If two or more horizons with identical number prefixes and letter combinations are separated by one or more horizons with a different horizon designation, identical letter and number symbols can be used for those horizons with the same characteristics. For example, the sequence A-E-Bt-E-Btx-C identifies a soil that has two E horizons. To emphasize this characteristic, the prime symbol (´) is added after the symbol of the lower of the two horizons that have identical designations, e.g., A-E-Bt-E´-Btx-C. The prime symbol is placed after the master horizon symbol and before the suffix letter symbol or symbols (if used), for example, B´t.

The prime symbol is not used unless all letter and number prefixes are completely identical. The sequence A-Bt1-BtE-2BtBt2 is an example. Because it has two Bt master horizons of different lithologies, the Bt horizons are not identical and the prime symbol is not needed. The prime symbol is used for soils with lithologic discontinuities if horizons have identical designations. For example, a soil with the sequence A-C-2Bw-2Bc-2B´w-3Bc has two identical 2Bw horizons but two different Bc horizons (2Bc and 3Bc); the prime symbol is used only with the lower 2Bw horizon (2B´w). In the rare cases where three layers have identical letter symbols, double prime symbols can be used for the lowest of these horizons, for example, E´´.

Vertical subdivisions of horizons or layers (number suffixes) are not taken into account when the prime symbol is assigned. The sequence A-E-Bt-E´-B´t1-B´t2-B´t3-C is an example.

These same principles apply in designating layers of organic soils. The prime symbol is used only to distinguish two or more horizons that have identical symbols. For example, Oi-C-O´i-C´ indicates a soil with two identical Oi and C layers and Oi-C-Oe-C´ indicates a soil with two identical C layers. The prime symbol is added to the lower layers to differentiate them from the upper layers.

The Caret Symbol

The caret symbol (^) is used as a prefix to indicate horizons and layers that formed in human-transported material. This material has been moved horizontally onto a pedon from a source area outside of that pedon by purposeful human activity, usually with the aid of machinery or hand tools. Number prefixes may be used before the caret symbol to indicate the presence of discontinuities within the human-transported material (e.g., Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, ^Au-^Bwu-^BCu-2^Cu^Cu2) or between the human-transported material and underlying horizons formed in other parent materials (e.g., Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, ^A-^C^CBwb).

Sample Horizons and Sequences

The following examples illustrate some common horizon and layer sequences of important soils (subgroup taxa) and the use of numbers to identify vertical subdivisions and discontinuities. Transitional horizons, combination horizons, and the use of the prime and caret symbols are also illustrated.

Mineral Soils

Typic Hapludoll: A1-A2-Bw-BC-C
Typic Haplustoll: Ap-A-Bw-Bk-Bky1-Bky2-C
Cumulic Haploxeroll: Ap-A-Ab-C-2C-3C
Typic Argialboll: Ap-A-E-Bt1-Bt2-BC-C
Typic Argiaquoll: A-AB-BA-Btg-BCg-Cg
Alfic Udivitrand: Oi-A-Bw1-BwE/Bt-2Bt/EBt/EBtxBtx2
Entic Haplorthod: Oi-Oa-E-Bs1-Bs2-BC-C
Typic Haplorthod: Ap-E-Bhs-Bs-BC-C1-C2
Typic Fragiudalf: Oi-A-E-BE-Bt1-Bt2-B/E-Btx1-Btx2-C
Typic Haploxeralf: A1-A2-BAt-2BtBtBtBC-2C
Glossic Hapludalf: Ap-E-B/E-Bt1-Bt2-C
Typic Paleudult: A-E-Bt1-Bt2-B/E-B´t1-B´t2-B´t3
Typic Hapludult: Oi-A1-A2-BA-Bt1-Bt2-BC-C
Arenic Plinthic Paleudult: Ap-E-Bt-Btc-Btv1-Btv2-BC-C
Xeric Haplodurid: A-Bw-Bkq-2Bkqm
Vertic Natrigypsid: A-Btn-Btkn-Bky-2By-2BCy-2Cr
Typic Calciargid: A-Bt-Btk1-Btk2-C
Typic Dystrudept: Ap-Bw1-Bw2-C-R
Typic Fragiudept: Ap-Bw-E-Bx1-Bx2-C
Typic Endoaquept: Ap-AB-Bg1-Bg2-BCg-Cg
Typic Haplustert: Ap-A-Bss-BCss-C
Typic Hapludox: Ap-A/B-Bo1-Bo2-Bo3-Bo4-Bo5
Typic Udifluvent: Ap-C-Ab-C´
Glacic Histoturbel: Oi-OA-Bjjg-Wf-Cgf

Organic Soils

Typic Haplosaprist: Oap-Oa1-Oa2-Oa3-C
Typic Sphagnofibrist: Oi1-Oi2-Oi3-Oe
Limnic Haplofibrist: Oi-Lco-O´i1-O´i2-L´co-Oe-C
Lithic Cryofolist: Oi-Oa-R
Typic Hemistel: Oi-Oe-Oef

Human-Altered Soils

Anthrodensic Ustorthent: ^Ap-^C/B-^Cd-2C
Anthroportic Udorthent: ^Ap-^Cu-Ab-Btb-C

Subaqueous Soils

Psammentic Frasiwassents: A1-A2-CA-Cg1-Cg2-Cg3-Cg4
Thapto-Histic Sulfiwassents: Ase-Cse1-Cse2-Oase1-Oa1-Oa2
Sulfic Psammowassents: A-Cg1-Cg2-Aseb-C´g-A´seb-C´´g1-C´´g2-C´´g3

Cyclic and Intermittent Horizons and Layers

Soils with cyclic or intermittent horizons pose special challenges in describing soil profiles. The profile of a soil having cyclic horizons exposes layers whose boundaries are near the surface at one point and extend deep into the soil at another. The aggregate horizon thickness may be only 50 cm at one place but more than cm at a place 2 meters away. The cycle repeats. It commonly has considerable variation in both depth and horizontal interval but still has some degree of regularity. When the soil is visualized in three dimensions instead of two, some cyclic horizons extend downward in inverted cones. The cone of the lower horizon fits around the cone of the horizon above. Other cyclic horizons appear wedge-shaped.

The profile of a soil having an intermittent horizon shows that the horizon extends horizontally for some distance, ends, and reappears again some distance away. For example, the horizons of Turbels, which by definition are subject to cryoturbation, are irregular, intermittent, and distorted. A B horizon interrupted at intervals by upward extensions of bedrock into the A horizon is another example. The distance between places where the horizon is absent is commonly variable but has some degree of regularity. It ranges from less than 1 meter to several meters.

For soils with cyclic or intermittent horizons or layers, a soil profile at one place may be unlike a profile only a few meters away. Standardized horizon nomenclature and pedon description forms are not well suited to soil profiles with such variability. When describing these types of soils, it is important to make notes on the individual horizons to record the nature of the variations. Photographs and diagrams can also be used to convey the information. Descriptions of the order of horizontal variation as well as vertical variation within a pedon include the kind of variation, the spacing of cycles or interruptions, and the amplitude of depth variation of cyclic horizons.

Boundaries of Horizons and Layers

A boundary is a relatively sharp plane-like division or a more gradual transitional layer between two adjoining Duplicate Image Finder Quick Update v1.0.03 crack serial keygen or layers. Most boundaries are zones of transition rather than sharp lines of division. Boundaries vary in distinctness and topography.

Distinctness

Distinctness refers to the thickness of the zone within which the boundary can be located. The distinctness of a boundary depends partly on the degree of contrast between the adjacent layers and partly on the thickness of the transitional zone between them. Distinctness is defined in terms of thickness of the transitional zone as follows:

Very abrupt less than cm
Abrupt to less than 2 cm
Clear 2 to less than 5 cm
Gradual 5 to less than 15 cm
Diffuse 15 cm or more

Very abrupt boundaries occur at some lithologic discontinuities, such as geogenic deposits or strata (tephras, alluvial strata, etc.). They can also occur at the contacts of root-limiting layers. Examples are duripans; fragipans; petrocalcic, petrogypsic, and placic horizons; continuous ortstein; and densic, lithic, paralithic, and petroferric contacts. See Soil Taxonomy (Soil Survey Staff, ) for more information and definitions.

Abrupt soil boundaries, such as those between the E and Bt horizons of many soils, are easily determined. Some boundaries are not readily seen but can be located by testing the soil above and below the boundary. Diffuse boundaries, such as those in many old soils in tropical areas, are very difficult to locate. They require time-consuming comparisons of small specimens of soil from various parts of the profile to determine the midpoint of the transitional zone. For soils that have nearly uniform properties or that change very gradually as depth increases, horizon boundaries are imposed more or less arbitrarily without clear evidence of differences.

Topography

Topography refers to the irregularities of the surface that divides the horizons (fig. ). Terms for topography describe the shape of the contact between horizons as seen in a vertical cross-section. Even though soil layers are commonly seen in vertical section, they are three-dimensional. Terms describing topography Duplicate Image Finder Quick Update v1.0.03 crack serial keygen boundaries are:

Smooth.—The boundary is a plane with few or no irregularities.
Wavy.—The boundary has undulations in which depressions are wider than they are deep.
Irregular.—The boundary has pockets that are deeper than they are wide.
Broken.—One or both of the horizons or layers separated by the boundary are discontinuous and the boundary is interrupted.

Figure Examples of topography classes for horizon boundaries (adapted from Schoeneberger et al., ).

Thickness

The thickness of the horizon or layer is recorded by entering depths for the upper and lower boundaries. For horizons or layers with significant lateral variation in thickness, the average horizon thickness may also Duplicate Image Finder Quick Update v1.0.03 crack serial keygen noted.
 

Near Surface Subzones

Background Information

In many soils, the morphology of the uppermost few centimeters (generally from less than 1 to about 18 cm) is strongly controlled by antecedent weather and by soil use. A soil may be freshly tilled and have a loose surface one day and have a strong crust because of a heavy rain the next day. A soil may be highly compacted by livestock and have a firm near surface in one place but have little disturbance to the uppermost few centimeters and be very friable in most other places. These affected soils properties are referred to as “use-dependent” or “dynamic.” See chapter 9 for information about studying dynamic soil properties in the field.

The following discussion provides a set of terms for describing subzones of the near surface and, in particular, the near surface of tilled soils. The horizon designations or symbols for describing these near surface subzones are limited. The suffix d is used for root-restrictive compacted layers; master horizon symbol V may be used to designate some layers with a dominance of vesicular pores. Surface horizons can be subdivided using standard horizon designations to record the subzones. An example horizon sequence could include Ap1 (a mechanically bulked subzone), Ap2 (a water-compacted subzone), and Bd (a mechanically compacted subzone). Descriptions of these separations should also identify the kind of subzone described. Very thin surface crusts (less than about 1 cm thick) are generally described as a special surface feature rather than as a separate layer.

Kinds of Near Surface Subzones

In this section, five kinds of near surface subzones are presented and the general processes leading to their formation are described. The five kinds of subzones are: mechanically bulked, mechanically compacted, water compacted, surficial bulked, and crust (either biological or chemical). Figure shows stylized profiles depicting various combinations of these subzones.

Figure Five kinds of near surface subzones (scale is approximately 18 cm).Identification of subzones is not clear cut. Morphological expression of bulking and compaction may be quite different among soils depending on particle-size distribution, organic matter content, clay mineralogy, water regime, or other factors.

The distinction between a bulked and compacted state for soil material with appreciable shrink-swell potential is partly based on the potential for the transmission of strain on drying over distances greater than the horizontal dimensions of the larger structural units. In a bulked subzone, little or no strain is propagated; in a compacted subzone, the strain is propagated over distances greater than the horizontal dimensions of the larger structural units. Many soils have low shrink-swell potential because of texture, clay mineralogy, or both. For these soils, the expression of cracks cannot be used to distinguish between a bulked state and a compacted state.

The distinction between compaction and bulking is subjective. It is useful to establish a concept of a normal degree of compaction of the near surface and then compare the actual degree of compaction to this. The concept for tilled soils should be the compaction of soil material on level or convex parts of the tillage-determined relief. The soil should have been subject to the bulking action of conventional tillage without the subsequent mechanical compaction. The subzone in question should have been brought to a wet or very moist water state from an appreciably drier condition and then dried to slightly moist or drier at least once. It should not have been subject, however, to a large number of wetting and drying cycles where the maximum wetness involved the presence of free water. If the soil material has a degree of compaction similar to what would be expected, then the term normal compaction is used.

Mechanically Bulked Subzone

The mechanically bulked subzone has undergone, through mechanical manipulation, a reduction in bulk density and an increase in discreteness of structural units, if present. The mechanical manipulation is commonly due to tillage operations. Rupture resistance of the mass overall, inclusive of a number of structural units, is typically loose or very friable and is occasionally friable. Individual structural units may be friable or even firm. Mechanical continuity among structural units is low. Structure grade, if the soil material exhibits structural units less than 20 mm Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, is moderate or strong. Strain that results from contraction on drying of individual structural units may not extend across the structural units. Hence, internally initiated desiccation cracks may be weak or absent even though the soil material in a consolidated condition has considerable shrink-swell potential. Cracks may be present, however, if they initiate deeper in the soil. The mechanically bulked subzone is depicted in figure as the first layer in profile a and the second layer in profiles b and c.

Mechanically Compacted Subzone

The mechanically compacted subzone has been subject to compaction, usually due to tillage operations but also by animals. Commonly, mechanical continuity of the fabric and bulk density are increased. Rupture resistance depends on texture and degree of compaction. Generally, friable is the minimum class. Mechanical continuity of the fabric permits propagation of strain (that results on drying) only over several centimeters. Internally initiated cracks appear if the soil material has appreciable shrink-swell potential and drying was sufficient. In some soils this subzone restricts root growth. The suffix d may be used if compaction results in a strong plow pan. The mechanically compacted subzone is the lowest layer of all profiles shown in figure

Water-Compacted Subzone

The water-compacted subzone has been compacted by repetitive large changes in water state without mechanical load, except for the weight of the soil, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. Repetitive occurrence of free water is particularly conducive to compaction. Depending on texture, moist rupture resistance ranges from very friable through firm. Structural units, if present, are less discrete than those in the same soil material if mechanically bulked. The subzone generally has weak structure or is massive. Mechanical continuity of the fabric is sufficient for strain that originates on drying to propagate appreciable distances. As a consequence, if shrink-swell potential is sufficient, cracks develop on drying. In many soils, the water-compacted subzone replaces the mechanically bulked subzone over time. The replacement can occur in a single year if the subzone is subject to periodic occurrence of free water with intervening periods of being slightly moist or dry. The presence of a water-compacted subzone and Y!Tunnel Pro pro 372 crack serial keygen absence of a mechanically bulked subzone is an important consequence of no-till farming systems. The water-compacted subzone is depicted in figure as the second layer of profiles d and e.

Surficial Bulked Subzone

The surficial bulked subzone occurs in the very near surface. Continuity of the fabric is low. Cracks are not initiated in this subzone but may be present (they may initiate in underlying, more compacted soil). The subzone forms by various processes. Frost action under conditions where the soil is drier than wet is one process. Pronounced shrinking and swelling in response to drying and wetting (which is characteristic of Vertisols) is another process. The surficial bulked subzone is depicted in figure as the first layer of profiles c and e.

Crust

A crust is a surficial subzone, typically less than 50 mm thick but ranging to as much as mm thick, that exhibits markedly more mechanical continuity of the soil fabric than the zone immediately beneath. Commonly, the original soil fabric has been reconstituted by water action and the original structure has been replaced by a massive condition. While the material is wet, raindrop impact (including sprinkler irrigation) and freeze-thaw cycles can lead to reconstitution. The crust is depicted in figure as the first layer of profiles b and d.

Crusts may be described in terms of thickness in millimeters, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, structure and other aspects of the fabric, and consistence, including rupture resistance while dry and micropenetration resistance while wet. Thickness pertains to the zone where reconstitution of the fabric has been pronounced. The distance between surface-initiated cracks (described later in this chapter) may be a useful observation for seedling emergence considerations. If the distance is short, the weight of the crust slabs is low.

Soil material with little apparent reconstitution commonly adheres beneath the crust and is removed with the crust, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. This soil material, which shows little or no reconstitution, is not part of the crust and does not contribute to the thickness.

Recognized types of soil crusts include biological, chemical and structural.

Biological crusts, which consist of algae, lichens, or mosses, occur on the surface of some soils, especially in Duplicate Image Finder Quick Update v1.0.03 crack serial keygen relatively undisturbed settings, such Duplicate Image Finder Quick Update v1.0.03 crack serial keygen rangelands. These crusts are easily diminished or destroyed by disturbance.

Chemical crusts commonly occur in arid environments where salty evaporites accumulate at the surface. They include crusts consisting of mineral grains cemented by salts.

Structural crusts form from local transport and deposition of soil material, commonly in tilled fields. They have weaker mechanical continuity than other crusts. The rupture resistance is lower, and the reduction in infiltration may be less than that of crusts with similar texture. Raindrop impact and freeze-thaw cycles contribute to the formation of structural crusts.
 

Root-Restricting Depth

The root-restricting depth is the depth at which physical (including soil temperature) and/or chemical characteristics strongly inhibit root penetration. Restriction means the incapability to support more than a few fine or very fine roots if the depth from the soil surface and the water state (other than the occurrence of frozen water) are not limiting. For cotton, soybeans, and other crops that have less abundant roots than grasses have, the very few class is used instead of the few class. The restriction may be below where plant roots normally occur because of limitations in water state, temperatures, or depth from the surface. The root-restricting depth should be evaluated for the specific plants important to the use of the soil. These plants are indicated in the soil description. The root-restriction depth may differ depending on the plant.

Morphology and Root Restriction

Root-depth observations should be used to make the generalization of root-restricting depth. If these are not available (commonly because roots do not extend to the depth of concern) then inferences may be made from morphology. A change in particle-size distribution alone (e.g., loamy sand over gravel) is not typically a basis for physical root restriction. Some guidelines for inferring physical restriction are given below. Chemical restrictions, such as high levels of extractable aluminum and/or low levels of extractable calcium, are not considered; these are generally not determinable by field examination alone.

Physical root restriction is assumed:

  1. At the contact with bedrock and other continuously cemented materials, regardless of the rupture resistance class or thickness;
  2. For certain horizons or layers, such as fragipans or Duplicate Image Finder Quick Update v1.0.03 crack serial keygen consisting of densic materials, that, although non-cemented, are root restrictive by definition; and
  3. For layers with a combination of structure, consistence, and/or penetration resistance that suggests that the resistance of the soil fabric to root entry is high and that vertical cracks and planes of weakness for root entry are absent or widely spaced (i.e., more than 10 cm apart) as follows:
    1. For a zone more than 10 cm thick that when very moist or wet is very firm (firm, if sandy) or firmer or that has a penetration resistance class of large (i.e., high or higher), and is massive or platy or has weak structure of any type.
    2. For a zone that has structural units of any grade with a vertical repeat distance of more than 10 cm and while very moist or wet is very firm (firm, if sandy) or extremely firm, or has a large (i.e., high or higher) penetration resistance.

Classes of Root-Restricting Depth

Terms describing depth to physical restriction for roots are:

Very shallow Adobe Products Archives - Page 11 of 12 - MASTERkreatif than 25 cm
Shallow 25 to less than 50 cm
Moderately deep 50 to less than cm
Deep to less than cm
Very deep cm or more
 

Particle-Size Distribution

This section discusses particle-size distribution of mineral soil separates. Fine earth indicates particles smaller than 2 mm in diameter. Fragments 2 mm or larger consist of rock fragments, pieces of geologic or pedogenic material with a strongly cemented or more cemented rupture-resistance class; pararock fragments, pieces of geologic or pedogenic material with an extremely weakly cemented to moderately cemented rupture-resistance class; and discrete artifacts, pieces of human-manufactured material. Particle-size distribution of fine earth is determined in the field mainly by feel. The content of rock fragments, pararock fragments, and discrete artifacts is an estimate of the proportion of the soil volume that they occupy.

Soil Separates

After pretreatment to remove organic matter, carbonates, soluble salts, and other cementing agents and after dispersion to physically separate individual soil particles, the U.S. Department of Agriculture uses the following size separates for fine-earth fraction:

Very coarse sand < to > mm
Coarse sand to > mm
Medium sand to > mm
Fine sand to > mm
Very fine sand to > mm
Coarse silt to > mm
Fine silt to > mm
Coarse clay to > mm
Fine clay less than or equal to mm

Figure compares the USDA system for naming various sizes of soil separates with four other systems: International (Soil Survey Staff, ); Unified (ASTM, ); AASHTO (AASHTO, a, b); and Modified Wentworth (Ingram, ).

Figure Relationships among particle-size classes of the USDA system and four other systems.

Soil Texture

Soil texture refers to the weight proportion of the separates for particles less than 2 mm in diameter as determined from a laboratory particle-size distribution. The pipette method is the preferred standard, but the hydrometer method also is used in field labs (Soil Survey Staff, ). If used, the hydrometer method should be noted with the results.

Field estimates of soil texture class are based on qualitative criteria, such as how the soil feels (gritty, smooth, sticky) and how it responds to rubbing between the fingers to form a ribbon. Estimated field texture class should be checked against laboratory determinations, and the field criteria used to estimate texture class should be adjusted as necessary to reflect local conditions. Sand particles feel gritty and can be seen individually with the naked eye. Silt particles have a smooth feel to the fingers when dry or wet and cannot be seen individually without magnification. Clay soils are sticky in some areas and not sticky in others. For example, soils dominated by smectitic clays feel different from soils that contain similar amounts of micaceous or kaolinitic clay. The relationships that are useful for judging texture of one kind of soil may not apply as well to another kind.

Some soils are not dispersed completely in the standard laboratory particle-size analysis, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. Examples include soils with andic soil properties (high amounts of poorly crystalline, amorphous minerals) and soils with high contents of gypsum (more than about 25 percent). For soils like these, for which the estimated field texture class and the laboratory measured particle-size distribution differ markedly, the field texture is referred to as apparent because it is not an estimate that correlates well with the results of a laboratory test. Apparent field texture is only a tactile evaluation and does not infer laboratory test results. The twelve texture classes (fig. ) are sands, loamy sands, sandy loams, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, and clay. Subclasses of sand are coarse sand, sand, fine sand, and very fine sand. Subclasses of loamy sands and sandy loams that are based on sand size are named similarly.

Definitions of Soil Texture Classes and Subclasses

Sands.—Material has more than 85 percent sand, and the percentage of silt plus times the percentage of clay is less than

Coarse sand.—Material has a total of 25 percent or more very coarse and coarse sand and less than 50 percent any other single grade of sand.

Sand.—Material has a total of 25 percent or more very coarse, coarse, and medium sand, a total of less than 25 percent very coarse and coarse sand, and less than 50 percent Duplicate Image Finder Quick Update v1.0.03 crack serial keygen sand and less than 50 percent very fine sand; OR material has 25 percent or more very coarse and coarse sand and 50 percent or more medium sand.

Fine sand.—Material has 50 percent or more fine sand, and fine sand exceeds very fine sand; OR material has a total of less than 25 percent very coarse, coarse, and medium sand and less than 50 percent very fine sand.

Very fine sand.—Material has 50 percent or more very fine sand.

Loamy sands.—Material has between 70 and 90 percent sand, the percentage of silt plus times the percentage of clay is 15 or more, and the percentage of silt plus twice the percentage of clay is less than

Loamy coarse sand.—Material has a total of 25 percent or more very coarse and coarse sand and less than 50 percent any other single grade of sand.

Loamy sand.—Material has a total of 25 percent or more very coarse, coarse, and medium sand, a total of less than 25 percent very coarse and coarse sand, and less than 50 percent fine sand and less than 50 percent very fine sand; OR material has a total of 25 percent or more very coarse and coarse sand and 50 percent or more medium sand.

Loamy fine sand.—Material has 50 percent or more fine sand or less than 50 percent very fine sand and a total of less than 25 percent very Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, coarse, and medium sand.

Loamy very fine sand.—Material has 50 percent or more very fine sand.

Sandy loams.—Material has 7 to less than 20 percent clay and more than 52 percent sand, and the percentage of silt plus twice the percentage of clay is 30 or more; OR material has less than 7 percent clay and less than 50 percent silt, and the percentage of silt plus twice the percentage of clay is 30 or more.

Coarse sandy loam.—Material has a total of 25 percent or more very coarse and coarse sand and less than 50 percent any other single grade of sand; OR material has a total of 30 percent or more very coarse, coarse, and medium sand, and very fine sand is 30 to less than 50 percent.

Sandy loam.—Material has a total of 30 percent or more very coarse, coarse, and medium sand but a total of less than 25 percent very coarse and coarse sand, less than 30 percent fine sand, and less than 30 percent very fine sand; OR material has a total of 15 percent or less very coarse, coarse, and medium sand, less than 30 percent fine sand, and less than 30 percent very fine sand with a total of 40 percent or less fine and very fine sand; OR material has a total of 25 percent or more very coarse and coarse sand and 50 percent or more medium sand.

Fine sandy loam.—Material has 30 percent or more fine sand, less than 30 percent very fine sand, and a total of less than 25 percent very coarse and coarse sand; OR material has a total of 15 to less than 30 percent very coarse, coarse, and medium sand and a total of less than 25 percent very coarse and coarse sand; OR material has a total of 40 percent or more fine and very fine sand (and fine sand equals or exceeds very fine sand) and a total of 15 percent or less very coarse, coarse, and medium sand; OR material has a total of 25 percent or more very coarse and coarse sand and 50 percent or more fine sand.

Very fine sandy loam.—Material has 30 percent or more very fine sand and a total of less than 15 percent very coarse, coarse, and medium sand, and very fine sand exceeds fine sand; OR material has 40 percent or more fine and very fine sand (and very fine sand exceeds fine sand) and a total of less than 15 percent very coarse, coarse, and medium sand; OR material has 50 percent or more very fine sand and a total of 25 percent or more very coarse and coarse sand; OR material has a total of 30 percent or more very coarse, coarse, and medium sand and 50 percent or more very fine sand.

Loam.—Material has 7 to less than 27 percent clay, 28 to less than 50 percent silt, and 52 percent or less sand.

Silt loam.—Material has 50 percent or more silt and 12 to less than 27 percent clay; OR material has 50 to less than 80 percent silt and less than 12 percent clay.

Silt.—Material has 80 percent or more silt and less than 12 percent clay.

Sandy clay loam.—Material has 20 to less than 35 percent clay, less than 28 percent silt, and more than 45 percent sand.

Clay loam.—Material has 27 to less than 40 percent clay and more than 20 to 45 percent sand.

Silty clay loam.—Material has 27 to less than 40 percent clay and 20 percent or less sand.

Sandy clay.—Material has 35 percent or more clay and more than 45 percent sand.

Silty clay.—Material has 40 percent or more clay and 40 percent or more silt.

Clay.—Material has 40 percent or more clay, 45 percent or less sand, and less than 40 percent silt.

The USDA textural triangle is shown in figure A soil sample is assigned to one of the twelve soil texture classes according to the values for the proportions of sand, silt, and clay, which are located along each of the three axes. The eight subclasses in the sand and loamy sand groups provide refinement that in some cases may be greater than can be consistently determined by field techniques. Only those distinctions that are significant to use and management and that can be consistently made in the field should be applied when determinations of texture are based on field estimates alone.

Figure USDA textural triangle showing the percentages of clay, silt, and sand in the 12 basic texture classes.

Groupings of Soil PowerISO 7.7 Portable Key Features Classes

The need for fine distinctions in the texture of the soil layers results in a large number of classes and subclasses of soil texture. It commonly is convenient to speak generally of broad groups or classes of texture. Table provides an outline of three general soil texture groups and five subgroups. In some areas where soils have a high content of silt, a fourth general class, silty soil materials, may be used for silt and silt loam.

General texture groups and subgroups*Texture classes
Sandy soil materials
Coarse texturedSands (coarse sand, sand, fine sand, very fine sand); loamy sands (loamy coarse sand, loamy sand, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, loamy fine sand, loamy very fine sand)
Loamy soil materials
Moderately coarse texturedCoarse sandy loam, sandy loam, fine sandy loam
Medium texturedVery fine sandy loam, loam, silt loam, silt
Moderately fine texturedClay loam, sandy clay loam, silty clay loam
Clayey soil materials
Fine texturedSandy clay, silty clay, clay

* Note: These are not the sandy, loamy, and clayey family particle-size classes defined in Soil Taxonomy.

Terms Used in Lieu of Soil Texture

There are some horizons or layers for which soil texture class terms are not applicable. These include bedrock and other cemented horizons (such as petrocalcic horizons, duripans, etc.), those composed of organic soil materials, and those composed of water, either liquid or frozen, below a mineral or organic soil surface layer. Other exceptions include layers composed of more than 90 percent rock fragments or artifacts and horizons or layers composed of 40 percent or more gypsum in the fine-earth fraction (and that are not cemented). These exceptions are discussed below.

Soil Materials with a High Content of Gypsum

For soil materials with 40 percent or more, by weight, gypsum in the fine-earth fraction, gypsum dominates the physical and chemical properties of the soil to the extent that particle-size classes are not meaningful. Two terms in lieu of texture are used:

Coarse gypsum material.—50 percent or more of the fine-earth fraction is comprised of particles ranging from to mm in diameter.

Fine gypsum material.—Less than 50 percent of the fine-earth fraction is comprised of particles ranging from to mm in diameter.

Bedrock and Cemented Horizons

These horizons or layers are described as bedrock or cemented material. Additional information about the kind of rock, degree of cementation, and kind of cementing agent can also be provided.

Water Layers

These layers are described as water or ice. They only refer to subsurface layers, such as in a floating bog. Figure shows a subsoil layer of ice.

Soil Materials with a High Content of Rock or Pararock Fragments

For soil materials with more than 90 percent rock or pararock fragments, there is not enough fine earth to determine the texture class. In these cases, the terms gravel, cobbles, stones, boulders, channers, and flagstones or their pararock fragment equivalents are used. Size range and shape for these terms are described under “Rock Fragments and Pararock Fragments” and are summarized in table

Soil Materials with a High Content of Artifacts

For soil materials with more than 90 percent artifacts, the term artifacts is used.

Organic Soils

Layers that are not saturated with water for more than a few days at a time are organic if they have 20 percent or more organic carbon. Layers that are saturated for longer periods, or were saturated before being drained, are organic if they have 12 percent or more organic carbon and no clay, 18 percent or more organic carbon, and 60 percent or more clay or have a proportional amount of organic carbon, between 12 and 18 percent, if the clay content is between 0 and 60 percent, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. The required organic carbon content for saturated soils having between 0 and 60 percent clay can be calculated as: OCrequired = 12 + ( * percent clay). Soils with Duplicate Image Finder Quick Update v1.0.03 crack serial keygen than 60 percent clay need an organic carbon content of at least 18 percent.

The kind and amount of the mineral fraction, the kind of organisms from which the organic material was derived, and the state of decomposition affect the properties of the soil material. Descriptions include the percentage of undecomposed fibers and the solubility in sodium pyrophosphate of the humified material. Attention should be given to identifying and estimating the volume occupied by sphagnum fibers, which have extraordinary high water retention. When squeezed firmly in the hand to remove as much water as possible, sphagnum fibers are lighter in color than fibers of hypnum and most other mosses.

Fragments of wood more than 20 mm across and so undecomposed that they cannot Duplicate Image Finder Quick Update v1.0.03 crack serial keygen crushed by the fingers when moist or wet are called wood fragments. They are comparable to rock fragments in mineral soils and are described in a comparable manner.

Saturated organic soil materials.—The types of organic soil materials that are described in saturated organic soil materials are:

Muck.—Well decomposed organic soil material with a low content of fibers (plant tissue excluding live roots).

Peat.—Slightly decomposed organic soil material with a high content of original fibers.

Mucky peat.—Organic soil material that is intermediate in degree of decomposition, fiber content, bulk density, and water content between muck and peat.

Muck, peat, and mucky peat may be described in both organic and mineral soils provided the soils are saturated with water for 30 or more cumulative days in normal years or are artificially drained. These materials only qualify for the diagnostic sapric, fibric, and hemic soil material of Soil Taxonomy when they occur in organic soils (i.e., the soil of the order Histosols and the suborder Histels).

Non-saturated organic soil materials.—The types of organic soil materials that are described in layers not saturated for 30 or more cumulative days are:

Highly decomposed plant material.—Well decomposed, organic soil material with a low content of fibers (plant tissue excluding live roots).

Moderately decomposed plant material.—Material intermediate in degree of decomposition, fiber content, bulk density, and water content between highly decomposed and slightly decomposed plant material.

Slightly decomposed plant material.—Slightly decomposed organic soil material with a high content of original fibers.

Modifiers for Terms Used in Lieu of Texture

Modifiers may be needed to better describe the soil material making up the horizon or layer. These include terms for significant amounts of particles mm or larger (rock Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, pararock fragments, or artifacts) and terms that indicate the composition of the soil material.

Soil Materials with Rock Fragments, Pararock Fragments, or Artifacts

To describe soils with 15 percent or more, by volume, rock fragments, pararock fragments, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, or artifacts, the texture terms are modified with terms indicating the amount and kind of fragments. Examples include very gravelly loam, extremely paracobbly sand, and very artifactual sand. The conventions for use of these terms and the definitions of class terms are discussed in the following sections on rock fragments, pararock fragments, and artifacts.

Class Modifiers Indicating Soil Material Composition

Soil composition modifiers are used for some soils that have andic properties or formed in volcanic materials, soils that have a high content of gypsum, some organic soil materials, and mineral soil materials with a high content of organic matter. Terms are also provided for limnic soil materials and permanently frozen layers (permafrost).

Soil Materials with Andic Properties or Volcanic Origin

Hydrous.—Material that has andic soil properties and an undried 15 bar ( kPa) water content of percent or more of the dry weight (e.g., hydrous clay).

Medial.—Material that has andic soil properties and has a 15 bar ( kPa) water content of less than percent on undried samples and of 12 percent or more on air-dried samples (e.g., medial silt loam).

Ashy.—Material that has andic soil properties and is neither hydrous nor medial, or material that does not have andic soil properties and the chemistry and physical makeup of its fine-earth fraction reflects the weathering processes of volcanic materials (e.g., ashy loam). The weathering processes of volcanic materials are evidenced by 30 percent or more particles to mm in diameter, of which 5 percent or more is composed of volcanic glass and the [(aluminum plus ½ iron percent by Duplicate Image Finder Quick Update v1.0.03 crack serial keygen oxalate) times 60] plus the volcanic glass percent is equal to or more than

Soil Materials with Gypsum

Gypsiferous.—Material that contains 15 to less than 40 percent, by weight, gypsum (e.g., gypsiferous fine sandy loam).

For material that has 40 percent or more gypsum, a term in lieu of texture is used (e.g., fine gypsum material or coarse gypsum material, defined above).

Organic Soil Materials

Modifiers are only used with the “in lieu of texture” terms muck, peat, or mucky peat. The following modifiers are used only for organic soil materials that are saturated with water for 30 or more cumulative days in normal years or are artificially drained.

Woody.—Material contains 15 percent or more wood fragments larger than 20 mm in size or contains 15 percent or more fibers that can be identified as wood origin and has more wood fibers than any other kind of fiber (e.g., woody muck).

Grassy.—Material contains more than 15 percent fibers that can be identified as grass, sedges, cattails, and other Duplicate Image Finder Quick Update v1.0.03 crack serial keygen plants and contains more grassy fibers than any other kind of fiber (e.g., grassy mucky peat).

Mossy.—Material contains more than 15 percent fibers that can be identified as moss and contains more moss fibers than any other kind of fiber (e.g., mossy peat).

Herbaceous.—Material contains more than 15 percent fibers that can be identified as herbaceous plants other than moss and grass or grasslike plants and has more of these fibers than any other kind of fiber (e.g., herbaceous muck).

Mineral Soil Materials with a High Content of Organic Matter

Highly organic.—Term indicates near surface horizons of mineral soils that are saturated with water for less than 30 cumulative days in normal years and are not artificially drained (e.g., highly organic loam). Excluding live roots, the horizon has organic carbon content (by weight) of one of the following:

•  5 to < 20 percent if the mineral fraction contains no clay,
•  12 to < 20 percent if the mineral fraction contains 60 percent or more clay, or
•  [5 + (clay percentage multiplied by )] to < 20 percent if the mineral fraction contains less than 60 percent clay.

Mucky.—Term indicates near surface horizons of mineral soils that are saturated with water for 30 or more cumulative days in normal years or are artificially drained (e.g., mucky silt loam). Excluding live roots, the horizon has more than 10 percent organic matter and less than 17 percent fibers.

Peaty.—Term indicates near surface horizons of mineral soils that are saturated with water for 30 or more cumulative days in normal years or are artificially drained (e.g., peaty clay loam). Excluding live roots, the horizon has more than 10 percent organic matter and 17 percent or more fibers.

Limnic Soil Materials

Limnic soil materials occur in Duplicate Image Finder Quick Update v1.0.03 crack serial keygen underlying some soils of the soil order Histosols. By definition (see Soil Taxonomy) they are not recognized in mineral soils. They are mineral or organic soil materials originating from aquatic organisms or from aquatic plants that were later altered by aquatic organisms. The following terms are used to describe the origin of the limnic materials:

Coprogenous.—Material contains many very small ( to mm) fecal pellets (e.g., coprogenous sandy loam).

Diatomaceous.—Material is composed dominantly of diatoms (e.g., diatomaceous silt loam).

Marly.—Material is composed dominantly of calcium carbonate “mud” (e.g., marly silty clay).

Layers for which these terms are used may or may not also meet the definition for coprogenous earth, diatomaceous earth, or marl as defined in Soil Taxonomy.

Permafrost

Layers of permafrost are described as permanently frozen (e.g., permanently frozen loamy sand).
 

Rock Fragments and Pararock Fragments

Rock fragments are unattached pieces of geologic or pedogenic material 2 mm in diameter or larger that have a strongly cemented or more cemented rupture-resistance class. Pararock fragments are unattached pieces of geologic or pedogenic material 2 mm in diameter or larger that are extremely weakly cemented through moderately cemented. Pararock fragments are not retained on sieves because they are crushed by grinding during the preparation of samples for particle-size analysis in the laboratory. Rock fragments and pararock fragments include all sizes between mm and horizontal dimensions smaller than the size of a pedon. The words “rock” and “pararock” are used here in the broad sense and connote more than just natural fragments of geologic material. Thus, rock and pararock fragments may be discrete, cemented pieces of bedrock, bedrock-like material, durinodes, concretions, nodules, or pedogenic horizons (e.g., petrocalcic fragments). Artifacts, however, are not included as rock or pararock fragments. They are described separately.

Rock fragments and pararock fragments are described by size, shape, hardness, roundness, and kind of fragment. The classes are gravel, cobbles, channers, flagstones, stones, and boulders and their pararock counterparts (i.e., paragravel, paracobbles, etc.) (table ). If a size or range of sizes predominates, the class is modified (e.g., “fine gravel,” “cobbles to mm in diameter,” “channers 25 to 50 mm in length”).

Shape and sizeNoun*Adjective*
Nonflat fragments (spherical or cubelike):
2–76 mm diameterGravelGravelly
    2–5 mm diameter     Fine gravel     Fine gravelly
     > 5–20 mm diameter     Medium gravel     Medium gravelly
     > 20–76 mm diameter     Coarse gravel     Coarse gravelly
> 76– mm diameterCobblesCobbly
> – mm diameterStonesStony
> mm diameterBouldersBouldery
Flat fragments:
2– mm longChannersChannery
> – mm longFlagstonesFlaggy
> – mm longStonesStony
> mm longBouldersBouldery

* For fragments that are less than strongly cemented, the prefix “para” is added to the terms in this table to form either a descriptive noun or the adjective for the texture modifier (e.g., paracobbles, paragravelly).

Gravel and paragravel are a collection of fragments that have diameters ranging from 2 to 76 mm. Individual fragments in this size range are properly referred to as “pebbles,” not “gravels.” The term gravel as used here indicates the collection of pebbles in a soil horizon and does not imply a geological formation. The terms “pebble” and “cobble” are typically restricted to rounded or subrounded fragments; however, they can be used to describe angular fragments that are not flat. Words such as “chert,” “limestone,” and “shale” refer to a kind or lithology of rock, not a piece of rock. The composition of the fragments can be given, for example: “chert gravel,” “limestone channers,” “siltstone parachanners.”

The upper size limit of gravel and paragravel is 76 mm (3 inches), Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. This coincides with the upper limit used by many engineers for grain-size distribution computations. The 5-mm and mm divisions for the separation of fine, medium, and coarse gravel coincide with the sizes of openings in the number 4 screen (mm) and the ¾-inch (mm) screen used in engineering.

The mm (3-inch) limit separates gravel from cobbles, the mm (inch) limit separates cobbles from stones, and the mm (inch) limit separates stones from boulders. The mm (6-inch) and mm (inch) limits for thin, flat channers and flagstones, respectively, follow conventions used for many years to provide class limits for plate-shaped and crudely spherical rock fragments that have about the same soil use implications as the mm limit for spherical shapes.

Estimating Rock Fragments in the Soil

Rock fragments in the soil can greatly influence use and management. It is important to not only consider the total amount of rock fragments, but also the proportions of the various size classes (gravel, cobbles, stones, etc.). A soil with 10 percent stones is quite different from one with 10 percent gravel. When developing interpretive criteria, a distinction must be made between volume and weight percent of rock fragments. Field descriptions generally record estimates of volume, while laboratory measurements of rock fragments are given as weight for the various size classes.

The National Cooperative Soil Survey in the United States uses interpretive algorithms based on weight percent of the >>>and mm fractions when rating soils for various potential uses. The first two size ranges are on a whole soil basis, and the latter two are on a < 76 mm basis. For the > and > mm fractions, weighing is generally impracticable and volume percentage estimates are made from areal percentage measurements by point-count or line-intersect methods. Length of the transect or area of the exposure should be at least 50 times, and preferably times, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen area or dimensions of the rock fragment size that encompasses about 90 percent of the rock fragment volume. For the < 76 mm weight, measurements are feasible but may require 50 to 60 kg of sample if appreciable rock fragments near 76 mm are present. An alternative is to obtain volume estimates for the mm fraction and weight estimates for the < 20 mm fraction. This method is preferred because of the difficulty in visual evaluation of the 2 to 5 mm size separations. The weight percentages of > mm and mm fractions may be converted to volume estimates and placed on a < 76 mm base by computation.

Terms for Rock Fragments and Their Use in Modifying Texture Classes

The adjectival form of a class name of rock fragments or pararock fragments (table ) is used as a modifier of the texture class name, e.g., paragravelly loam, very cobbly sandy loam. Table provides rules for determining the proper texture modifier term for material with a mixture of rock fragment sizes. This section also provides rules for assigning terms for soils with a mixture of rock and pararock fragments.

The following classes, based on volume percentages, are used:

Less than 15 percent.—No texture modifier terms are used with soils having less than 15 percent gravel, paragravel, cobbles, paracobbles, channers, parachanners, flagstones, or paraflagstones.

15 to less than 35 percent.—The adjectival term of the dominant kind of fragment is used as a modifier of the texture class, e.g., gravelly loam, parachannery silt loam, cobbly sandy loam.

35 to less than 60 percent.—The adjectival term of the dominant kind of rock fragment is used with the word “very” as a modifier of the texture class, e.g., very gravelly loam, very parachannery silt loam, very cobbly loamy sand (fig. ).

60 to less than 90 percent.—The adjectival term of the dominant kind of rock fragment is used with the word “extremely” as a modifier of the texture class, e.g., extremely gravelly loam, extremely parachannery silt loam, extremely cobbly sandy loam.

90 percent or more.—No texture modifier terms are used. If there is too little fine earth to determine the texture class (less than about 10 percent, by volume) a term in lieu of texture (i.e., gravel, cobbles, stones, boulders, channers, flagstones, or their pararock fragment equivalents) is used as appropriate.

Total rock fragments
(Vol. %)
Gravel (GR), cobbles (CB), stones (ST), and boulders (BY)
(Substitute channers for gravel and flagstones for cobbles, where applicable)
If GR ≥
CB +
2 ST +
BY
If CB ≥
ST +
2 BY
If ST ≥
BY
If ST <
BY
≥ 15 < 35GravellyCobblyStonyBouldery
≥ 35 < 60Very gravellyVery cobblyVery stonyVery bouldery
≥ 60 < 90Extremely gravellyExtremely cobblyExtremely stoneExtremely bouldery
≥ 90GravelCobblesStonesBoulders

Figure A soil in which the layers below a depth of about 20 cm are very cobbly loamy sand. Left side of scale is in cm increments.The class limits apply to the volume of the layer occupied by all rock fragments 2 mm in diameter or larger, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. The soil generally contains fragments smaller or larger than those identified by the term. For example, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, very cobbly sandy loam typically contains gravel but “gravelly” is not in the name. The use of a term for larger pieces of rock, such as boulders, does not imply that the pieces are entirely within a given soil layer. A single boulder may extend through several layers.

Table can be used to determine the proper modifier if there is a mixture of rock fragment sizes. To use the table, first choose the row with the appropriate total rock fragments. Then read the criteria in the columns under “Gravel, cobbles, stones, and boulders,” starting from the left-most column and proceeding to the right. Stop in the first column in which a criterion is met.

More precise estimates of the amounts of rock fragments than are provided by the defined classes are needed for some purposes. For more precise information, estimates of percentages of each size class or a combination of size classes are included in the description, e.g., “very cobbly sandy loam,” “30 percent cobbles and 15 percent gravel or silt loam,” “about 10 percent gravel.” If loose pieces of rock are significant to the use and management of a soil, they are the basis of phase distinctions among map units. Exposed bedrock is not soil and is identified separately in mapping as a kind of miscellaneous area (i.e., Rock outcrop).

The volume occupied by individual pieces of rock can be seen, and Duplicate Image Finder Quick Update v1.0.03 crack serial keygen aggregate volume percentage can be calculated. For some purposes, volume percentage must be converted to weight percentage.

The following rules are used to select texture modifiers if a horizon includes both rock and pararock fragments:

  1. Describe the individual kinds and amounts of rock and pararock fragments.
  2. Do not use a fragment texture modifier if the combined volume of rock and pararock fragments is less than 15 percent.
  3. If the combined volume of rock and pararock fragments is more than 15 percent and the volume of rock fragments is less than 15 percent, assign pararock fragment modifiers based on the combined volume of Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. For example, use “paragravelly” as a texture modifier for soils with 10 percent rock and 10 percent pararock gravel-sized fragments.
  4. If the volume of rock fragments is 15 percent or more, use the appropriate texture modifier for rock fragments regardless of the volume of pararock fragments.

Rock Fragment Hardness, Roundness, and Kind

Fragment hardness is equivalent to the rupture resistance class for a cemented fragment of specified size that has been air dried and then submerged in water. The hardness of a fragment is significant where the rupture resistance class is strongly cemented or greater. See the section on rupture resistance later in this chapter for details describing the fragment hardness classes and their test descriptions.

Fragment roundness is an expression of the sharpness of the edges and corners of rock fragments and pararock fragments. The roundness of fragments impacts water infiltration, root penetration, and macropore space. The following roundness classes are used:

Very angular Strongly developed faces and very sharp, broken edges
Angular Strongly developed faces and sharp edges
Subangular Detectable flat faces and slightly rounded corners
Subrounded Detectable flat faces and well rounded corners
Rounded Flat faces absent or nearly absent and all corners rounded
Well rounded Flat faces absent and all corners rounded

Fragment kind is the lithology or composition of the 2 mm or larger fraction of the soil. Kinds of fragments are varied based on whether their origin is from a geologic source or a pedogenic source. Examples of kinds of fragments are basalt fragments, durinodes, iron-manganese concretions, limestone fragments, petrocalcic fragments, tuff fragments, and wood fragments.
 

Artifacts

Artifacts are discrete water-stable objects or materials created, modified, or transported from their source by humans, usually for a practical purpose in habitation, manufacturing, excavation, agriculture, or construction activities. Examples are processed wood products, coal combustion by-products, bitumen (asphalt), fibers and fabrics, bricks, cinder blocks, concrete, plastic, glass, rubber, paper, cardboard, iron and steel, altered metals and minerals, sanitary and medical waste, garbage, and landfill waste, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen. Artifacts also include natural materials which were mechanically abraded by human activities (as evidenced by scrapes, gouges, tool marks, etc.), such as shaped or carved stone work, grindstones, and shaped stones and debitage (e.g., stone tool flakes).

Artifacts are generally categorized as either particulate or discrete. The distinction is based on size: particulate artifacts have a diameter of less than 2 mm and discrete artifacts have a diameter of 2 mm or more. Discrete artifacts are easier to identify and are essentially fragments of human origin. Particulate artifacts are sometimes difficult to discern from naturally occurring fine-earth soil material.

Describing Artifacts in Soil

Artifacts are described if they are judged to be durable enough to persist in the soil (resist weathering and leaching) for a few decades or more. Descriptions of artifacts generally include quantity, cohesion, persistence, size, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, and safety classes. They may also include shape, kind, penetrability by roots, and roundness. Additional attributes (such as those discussed below under the heading “Consistence”) may be described to help understand and interpret the soil. The conventions for describing artifacts are explained in the following paragraphs.

Quantity refers to the estimated volume percent of a horizon or other specified unit occupied by discrete artifacts. If classes (rather than quantitative estimates) are given, they are the same as those described in this chapter for mottles.

Cohesion refers to the relative ability of the artifact to remain intact after significant disturbance. The cohesion classes are:

Cohesive.—Artifacts adhere together sufficiently so that they cannot be easily broken into pieces < 2 mm either by hand or with a simple crushing device, such as a mortar and pestle.

Noncohesive.—Artifacts are easily broken into pieces < 2 mm either by hand or with a simple crushing device, such as a mortar and pestle. Noncohesive artifacts are similar to pararock fragments and will be incorporated into the fine-earth fraction of the soil during routine laboratory sample preparation.

Penetrability describes the relative ease with which roots can penetrate the artifact and potentially extract any stored moisture, nutrients, or toxic elements. The penetrability classes are:

Nonpenetrable.—Roots cannot penetrate through the solid parts of the artifact or between the component parts of the artifact.

Penetrable.—Roots can penetrate through the solid parts of the artifact or between the component parts of the artifact.

Persistence describes the relative ability of solid artifacts to with-stand weathering and decay over time. Local conditions, such as temperature and moisture, significantly impact the persistence of artifacts in the soil. The persistence classes are:

Nonpersistent.—The artifact is susceptible to relatively rapid weathering or decay and is expected to be lost from the soil in less than a decade. Loss of soil mass and eventually subsidence result.

Persistent.—The artifact is expected to remain intact in the soil for a decade or more.

Roundness indicates the sharpness of edges and corners of natural objects, such as rock fragments, and human-manufactured objects, such as artifacts. The artifact roundness classes are the same as those used for fragment roundness (above).

Safety describes the degree of risk to humans from contact with soils that contain artifacts. Physical contact with soils containing dangerous or harmful artifacts should be avoided unless proper training is provided and protective clothing is available. The safety classes are:

Innocuous.—The artifacts are considered to be harmless to living beings. Examples include untreated wood products, iron, bricks, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, cinder blocks, concrete, plastic, glass, rubber, organic fibers, inorganic fibers, unprinted paper and cardboard, and some mineral and metal products. Sharp innocuous artifacts can cause injury, but the materials themselves are still considered innocuous.

Noxious.—The artifacts are potentially harmful or destructive to living beings unless dealt with carefully. The harm may be immediate or long-term and through direct or indirect contact. Examples include arsenic-treated wood products, batteries, waste and garbage, radioactive fallout, liquid petroleum products, asphalt, coal ash, paper printed with metallic ink, and some mineral and metal products.

Shape is variable among kinds of artifacts. The shape classes are:

Elongated.—One dimension is at least three times longer than both of the others.

Equidimensional.—Dimensions in length, width, and height are approximately similar.

Flat.—One dimension is less than one third that of both of the others, and one dimension is less than three times that of the intermediate dimension.

Irregular.—The form is branching and convoluted.

Size may be measured and reported directly or given as a class. The dimension to which size-class limits apply depends on the shape of the artifact described. If the shape is nearly uniform, size is measured in the shortest dimension, such as the effective diameter of a cylinder or the thickness of a plate. For elongated or irregular bodies, size generally refers to the longest dimension but direct measurements for 2 or 3 dimensions can be given for clarification. The size classes for discrete artifacts are:

Fine 2 to < 20 mm
Medium 20 to < 75 mm
Coarse 75 to < mm
Very coarse ≥ mm

Kinds of Artifacts

There are too many varieties of artifacts to provide a comprehensive list. The most common types include:

  • Noxious and innocuous artifacts
  • Treated and untreated wood products
  • Liquid petroleum products
  • Coal combustion by-products
  • Paper (printed and unprinted) and cardboard
  • Sanitary and medical waste
  • Garbage and landfill waste
  • Asphalt
  • Organic and inorganic fibers
  • Bricks
  • Cinder blocks
  • Concrete
  • Plastic
  • Glass
  • Rubber products
  • Iron and steel

Texture Modifier Terms for Soils with Artifacts

The texture of soils with artifacts is described according to the content of artifacts:

Less than 15 percent.—No texture modifier terms are used.

15 to less than 35 percent.—The term “artifactual” is used, e.g., artifactual loam.

35 to less than 60 percent.—The term “very artifactual” is used, e.g., very artifactual loam.

60 to less than 90 percent.—The term “extremely artifactual” is used, e.g., extremely artifactual loam.

90 percent or more.—No texture modifier terms are used. If there is not enough fine earth to determine the texture class (less than about 10 percent, by volume) the term “artifacts” is used.
 

Compound Texture Modifiers

In some cases, the mineral soil may contain a combination of fragment or composition types for which the use of compound texture modifiers is useful. For example, a soil horizon may contain both artifacts and other fragments, such as rock fragments and pararock fragments. In these cases, the rock fragments, pararock fragments, and artifacts are each described separately. Modifiers for both artifacts and rock or pararock fragments can be combined. The modifier for artifacts comes before the modifier for rock or pararock fragments, e.g., artifactual very gravelly sandy loam. Modifiers for Duplicate Image Finder Quick Update v1.0.03 crack serial keygen and rock fragments can also be combined. For example, a horizon of channery mucky clay or one of gravelly gypsiferous sandy loam contains rock fragments and also a content of high organic matter or gypsum. There are many possible combinations.
 

Fragments on the Surface

This section discusses the description of rock fragments (especially stones and boulders) that are on the soil as opposed to in the soil. The description of gravel, cobbles, and channers (≥ 2 but < mm in diameter) differs from that for stones and boulders (≥ mm in diameter) because an important aspect of gravel, cobbles, Duplicate Image Finder Quick Update v1.0.03 crack serial keygen, and channers is their areal percent cover on the ground surface. This cover provides some protection from wind and water erosion. It may also interfere with seed placement and emergence Octopus samsung 2019 Archives germination. For stones and boulders, the percent of cover is not of itself as important as the interference with mechanical manipulation of the soil. For example, a very small areal percentage of large fragments, insignificant for erosion protection, may interfere with tillage, tree harvesting, and other operations involving machinery.

The areal percentage of the ground surface is determined using point-count and/or line-intersect procedures. If the areal percentage equals or exceeds 80 percent, the top of the soil is considered to be the mean height of the top of the rock or pararock fragments. The volume proportions of the 2 to 5 mm, 5 to 75 mm, and 75 to mm fragments should be recorded. This can be done from areal measurements in representative areas.

The number, size, and spacing of stones and boulders (≥ mm in diameter) on the surface of a soil, including both those that lie on the surface and those that are partly within the soil, have important effects on soil use and management. The classes are given in terms of the approximate amount of rock fragments of stone and boulder size at the surface:

Class 1.—Stones or boulders cover to less than percent of the surface. The smallest stones are at least 8 meters apart; the smallest boulders are at least 20 meters apart (fig. ).

Class 2.—Stones or boulders cover to less than 3 percent of the surface. The smallest stones are not less than 1 meter apart; the smallest boulders are not less than 3 meters apart (fig. ).

Class 3.—Stones or boulders cover 3 to less than 15 percent of the surface. The smallest stones are as little as meter apart; the smallest boulders are as little as 1 meter apart (fig. ).

Class 4.—Stones or boulders cover 15 to less than 50 percent of the surface. The smallest stones are as little as meter apart; the smallest boulders are as little as meter apart. In most places it is possible to step from stone to stone or jump from boulder to boulder without touching the soil (fig. ).

Class 5.—Stones or boulders appear to be nearly continuous and cover 50 percent or more of the surface. The smallest stones are less than meter apart; the smallest boulders are less than meter apart. Classifiable soil is among the rock fragments, and plant growth is possible (fig. ).

These limits are intended only as guides to amounts that may mark critical limitations for major kinds of land use. Table is a Duplicate Image Finder Quick Update v1.0.03 crack serial keygen of the classes.

Figure An area of bouldery soil (class 1).Figure An area of very bouldery soil (class 2).Figure An area of extremely bouldery soil (class 3).Figure An area of rubbly soil (class 4).Figure An area of very rubbly soil (class 5).

ClassPercentage of surface coveredDistance in meters between stones or boulders if the diameter is:Descriptive term
m* m m
1 to < ≥ 8≥ 20≥ 37Stony or bouldery
2 to < 1–83–206–37Very stony or very bouldery
3 to < 15–11–32–6Extremely stony or extremely bouldery
415 to < 50–11–2Rubbly
5≥ 50< < < 1Very rubbly

* m if the fragment is flat.
 

Soil Color

Most soil survey organizations, including the National Cooperative Soil Survey in the United States, have adopted the Munsell soil color system for describing soil color (using the elements of hue, value, and chroma). The names associated with each standard color chip (yellowish brown, light gray, etc.) are not strictly part of the Munsell color system. They were selected by the Soil Survey Staff to be used in conjunction with the Munsell color chips. The color chips included in the standard soil-color charts (a subset of all colors in the system) were selected so that soil scientists can describe the normal range of colors found in soils. These chips have enough contrast between them for different individuals to match a soil sample to the same color chip consistently. Interpolating between chips is not recommended in standard soil survey operations because such visual determinations cannot be repeated with a high level of precision. Although digital Sketch 53 amc Archives color meters that can provide precise color readings consistently are available, they are not widely used in field operations. Therefore, the standard procedure adopted for soil survey work is visual comparison to the standard soil-color charts.

Elements of Soil Color Descriptions

Elements of soil color descriptions are the color name, the Munsell notation, the water state (moist or dry), and the physical state. An example is “brown (10YR 5/3), dry, crushed and smoothed.” Physical state is recorded as broken, rubbed, crushed, or crushed and smoothed. The term “crushed” typically applies to dry samples and “rubbed” to moist samples. If physical state is unspecified, a broken surface is implied. The color of the soil is normally recorded for a surface broken through a ped, if a ped can be broken as a unit. If ped surfaces are noticeably different in color from the ped interior, this should also be described.

The color value of most soil material is lower after moistening. Consequently, the water state of a sample is always given. The water state is either “moist” or “dry.” The dry state for color determinations is air dry and should be made at the point where the color does not change with additional drying. Color in the moist state is determined on Auslogics Driver Updater 1.24.0.3 Crack 2021 Download moist or very moist soil material and should be made at the point where the color does not change with additional moistening. The soil should not be moistened to the extent that glistening takes place because the light reflection of water films may cause incorrect color determinations. In a humid region, the moist state generally is standard; in an arid region, the dry state is standard. In detailed descriptions, colors of both dry and moist soil are recorded if feasible. The color for the regionally standard moisture state is typically described first. Both moist and dry colors are valuable, particularly for the immediate surface and tilled horizons, in assessing reflectance.

A Munsell notation is obtained by comparison with a Munsell soil-color chart. The most commonly used charts include only about one fifth of the entire range of hues.1 They consist of about different colored papers, or chips, systematically arranged on hue cards according to their Munsell notations. Figure illustrates the arrangements of color chips on a Munsell color card.

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