Community hub
Recent from talks
Contribute something to knowledge base
Content stats: 0 posts, 0 articles, 0 media, 0 notes
Members stats: 0 subscribers, 0 contributors, 0 moderators, 0 supporters
Subscribers
Supporters
Contributors
Moderators
Hub AI
Soil horizon AI simulator
(@Soil horizon_simulator)
Hub AI
Soil horizon AI simulator
(@Soil horizon_simulator)
Soil horizon
A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. These may be described both in absolute terms (particle size distribution for texture, for instance) and in terms relative to the surrounding material, i.e. "coarser" or "sandier" than the horizons above and below.[citation needed]
The identified horizons are indicated with symbols, which are mostly used in a hierarchical way. Master horizons (main horizons) are indicated by capital letters. Suffixes, in form of lowercase letters and figures, further differentiate the master horizons. There are many different systems of horizon symbols in the world. No one system is more correct—as artificial constructs, their utility lies in their ability to accurately describe local conditions in a consistent manner. Due to the different definitions of the horizon symbols, the systems cannot be mixed.
In most soil classification systems, horizons are used to define soil types. The German system uses entire horizon sequences for definition. Other systems pick out certain horizons, the "diagnostic horizons", for the definition; examples are the World Reference Base for Soil Resources (WRB), the USDA soil taxonomy and the Australian Soil Classification. Diagnostic horizons are usually indicated with names, e.g. the "cambic horizon" or the "spodic horizon". The WRB lists 40 diagnostic horizons. In addition to these diagnostic horizons, some other soil characteristics may be needed to define a soil type. Some soils do not have a clear development of horizons.
A soil horizon is a result of soil-forming processes (pedogenesis). Layers that have not undergone such processes may be simply called "layers".
Many soils have an organic surface layer, which is denominated with a capital letter "O" (letters may differ depending on the system). The mineral soil usually starts with an A horizon. If a well-developed subsoil horizon as a result of soil formation exists, it is generally called a B horizon. An underlying loose, but poorly developed horizon is called a C horizon. Hard bedrock is mostly denominated R. Most individual systems defined more horizons and layers than just these five. In the following, the horizons and layers are listed more or less by their position from top to bottom within the soil profile. Not all of them are present in every soil.
Soils with a history of human interference, for instance through major earthworks or regular deep ploughing, may lack distinct horizons almost completely. When examining soils in the field, attention must be paid to the local geomorphology and the historical uses to which the land has been put, in order to ensure that the appropriate names are applied to the observed horizons.
The designations are found in Chapter 10 of the World Reference Base for Soil Resources Manual, 4th edition (2022). The chapter starts with some general definitions:
The fine earth comprises the soil constituents ≤ 2 mm. The whole soil comprises fine earth, coarse fragments, artefacts, cemented parts, and dead plant residues of any size.
Soil horizon
A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. These may be described both in absolute terms (particle size distribution for texture, for instance) and in terms relative to the surrounding material, i.e. "coarser" or "sandier" than the horizons above and below.[citation needed]
The identified horizons are indicated with symbols, which are mostly used in a hierarchical way. Master horizons (main horizons) are indicated by capital letters. Suffixes, in form of lowercase letters and figures, further differentiate the master horizons. There are many different systems of horizon symbols in the world. No one system is more correct—as artificial constructs, their utility lies in their ability to accurately describe local conditions in a consistent manner. Due to the different definitions of the horizon symbols, the systems cannot be mixed.
In most soil classification systems, horizons are used to define soil types. The German system uses entire horizon sequences for definition. Other systems pick out certain horizons, the "diagnostic horizons", for the definition; examples are the World Reference Base for Soil Resources (WRB), the USDA soil taxonomy and the Australian Soil Classification. Diagnostic horizons are usually indicated with names, e.g. the "cambic horizon" or the "spodic horizon". The WRB lists 40 diagnostic horizons. In addition to these diagnostic horizons, some other soil characteristics may be needed to define a soil type. Some soils do not have a clear development of horizons.
A soil horizon is a result of soil-forming processes (pedogenesis). Layers that have not undergone such processes may be simply called "layers".
Many soils have an organic surface layer, which is denominated with a capital letter "O" (letters may differ depending on the system). The mineral soil usually starts with an A horizon. If a well-developed subsoil horizon as a result of soil formation exists, it is generally called a B horizon. An underlying loose, but poorly developed horizon is called a C horizon. Hard bedrock is mostly denominated R. Most individual systems defined more horizons and layers than just these five. In the following, the horizons and layers are listed more or less by their position from top to bottom within the soil profile. Not all of them are present in every soil.
Soils with a history of human interference, for instance through major earthworks or regular deep ploughing, may lack distinct horizons almost completely. When examining soils in the field, attention must be paid to the local geomorphology and the historical uses to which the land has been put, in order to ensure that the appropriate names are applied to the observed horizons.
The designations are found in Chapter 10 of the World Reference Base for Soil Resources Manual, 4th edition (2022). The chapter starts with some general definitions:
The fine earth comprises the soil constituents ≤ 2 mm. The whole soil comprises fine earth, coarse fragments, artefacts, cemented parts, and dead plant residues of any size.