Soil type

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A soil type is a taxonomic unit in soil science. All soils that share a certain set of well-defined properties form a distinctive soil type. [1] Soil type is a technical term of soil classification, the science that deals with the systematic categorization of soils. Every soil of the world belongs to a certain soil type. Soil type is an abstract term. In nature, you will not find soil types. You will find soils that belong to a certain soil type.

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In hierarchical soil classification systems, soil types mostly belong to the higher or intermediate level. A soil type can normally be subdivided into subtypes, and in many systems several soil types can be combined to entities of higher category. However, in the first classification system of the United States (Whitney, 1909), [2] the soil type was the lowest level and the mapping unit.

For the definition of soil types, some systems use primarily such characteristics that are the result of soil-forming processes (pedogenesis). An example is the German soil systematics. [3] Other systems combine characteristics resulting from soil-forming processes and characteristics inherited from the parent material. Examples are the World Reference Base for Soil Resources [4] (WRB) and the USDA soil taxonomy. [5] Other systems do not ask whether the properties are the result of soil formation or not. An example is the Australian Soil Classification. [6]

A convenient way to define a soil type is referring to soil horizons. However, this is not always possible because some very initial soils may not even have a clear development of horizons. For other soils, it may be more convenient to define the soil type just referring to some properties common to the whole soil profile. For example, WRB defines the Arenosols by their sand content. Many soils are more or less strongly influenced by human activities. This is reflected by the definition of many soil types in various classification systems.

Because soil type is a very general and widely used term, many soil classification systems do not use it for their definitions. The USDA soil taxonomy has six hierarchical levels that are named order, suborder, great group, subgroup, family, and series. The WRB calls the first level Reference Soil Group. The second level in WRB is constructed by adding qualifiers, and for the result (the Reference Soil Group plus the qualifiers), no taxonomic term is used.

See also

Related Research Articles

<span class="mw-page-title-main">Soil science</span> Study of soil as a natural resource on the surface of Earth

Soil science is the study of soil as a natural resource on the surface of the Earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to the use and management of soils.

<span class="mw-page-title-main">Aridisol</span>

Aridisols are a soil order in USDA soil taxonomy. Aridisols form in an arid or semi-arid climate. Aridisols dominate the deserts and xeric shrublands, which occupy about one third of the Earth's land surface. Aridisols have a very low concentration of organic matter, reflecting the paucity of vegetative production on these dry soils. Water deficiency is the major defining characteristic of Aridisols. Also required is sufficient age to exhibit subsoil weathering and development. Limited leaching in aridisols often results in one or more subsurface soil horizons in which suspended or dissolved minerals have been deposited: silicate clays, sodium, calcium carbonate, gypsum or soluble salts. These subsoil horizons can also be cemented by carbonates, gypsum or silica. Accumulation of salts on the surface can result in salinization.

<span class="mw-page-title-main">Soil classification</span> Systematic categorization of soils

Soil classification deals with the systematic categorization of soils based on distinguishing characteristics as well as criteria that dictate choices in use.

<span class="mw-page-title-main">Mollisol</span> Nutrient-rich soil type

Mollisol is a soil type which has deep, high organic matter, nutrient-enriched surface soil, typically between 60 and 80 cm in depth. This fertile surface horizon, called a mollic epipedon, is the defining diagnostic feature of Mollisols. Mollic epipedons are created by long-term addition of organic materials derived from plant roots and typically have soft, granular soil structure.

<span class="mw-page-title-main">Gelisol</span> Permafrost soils

Gelisols are an order in USDA soil taxonomy. They are soils of very cold climates which are defined as containing permafrost within two meters of the soil surface. The word "Gelisol" comes from the Latin gelare meaning "to freeze", a reference to the process of cryoturbation that occurs from the alternating thawing and freezing characteristic of Gelisols.

<span class="mw-page-title-main">Vertisol</span> Clay-rich soil, prone to cracking

A vertisol is a Soil Order in the USDA soil taxonomy and a Reference Soil Group in the World Reference Base for Soil Resources (WRB). It is also defined in many other soil classification systems. In the Australian Soil Classification it is called vertosol. Vertisols have a high content of expansive clay minerals, many of them belonging to the montmorillonites that form deep cracks in drier seasons or years. In a phenomenon known as argillipedoturbation, alternate shrinking and swelling causes self-ploughing, where the soil material consistently mixes itself, causing some vertisols to have an extremely deep A horizon and no B horizon.. This heaving of the underlying material to the surface often creates a microrelief known as gilgai.

<span class="mw-page-title-main">Histosol</span> Soil consisting primarily of organic materials

In both the World Reference Base for Soil Resources (WRB) and the USDA soil taxonomy, a Histosol is a soil consisting primarily of organic materials. They are defined as having 40 centimetres (16 in) or more of organic soil material starting within 40 cm from the soil surface. In Soil Taxonomy, Gelisols key out before Histosols, and in WRB, Histosols key out before Cryosols. Therefore, organic permafrost soils belong to the Histosols in WRB and to the Gelisols (Histels) in Soil Taxonomy.

In USDA soil taxonomy, a Psamment is defined as an Entisol which consists basically of unconsolidated sand deposits, often found in shifting sand dunes but also in areas of very coarse-textured parent material subject to millions of years of weathering. This latter case is characteristic of the Guiana Highlands of northern South America. A Psamment has no distinct soil horizons, and must consist entirely of material of loamy sand or coarser in texture. In the World Reference Base for Soil Resources (WRB), most Psamments belong to the Arenosols. However, Psamments of fluviatile, lacustrine or marine origin belong to the Fluvisols.

<span class="mw-page-title-main">World Reference Base for Soil Resources</span> International soil classification system

The World Reference Base for Soil Resources (WRB) is an international soil classification system for naming soils and creating legends for soil maps. The currently valid version is the fourth edition 2022. It is edited by a working group of the International Union of Soil Sciences (IUSS).

<span class="mw-page-title-main">Gypsisol</span>

Gypsisols in the World Reference Base for Soil Resources (WRB) are soils with substantial secondary accumulation of gypsum (CaSO4.2H2O). They are found in the driest parts of the arid climate zone. In the USDA soil taxonomy they are classified as Gypsids (USDA Soil Taxonomy), in the Russian soil classification they are called Desert soils (USSR).

<span class="mw-page-title-main">Acrisol</span>

An Acrisol is a Reference Soil Group of the World Reference Base for Soil Resources (WRB). It has a clay-rich subsoil and is associated with humid, tropical climates, such as those found in Brazil, and often supports forested areas. In the USDA soil taxonomy, Acrisols correspond to the Humult, Udult and Ustult suborders of the Ultisols and also to Oxisols with a kandic horizon and to some Alfisols. The Acrisols low fertility and toxic amounts of aluminium pose limitations to its agricultural use, favouring in many places its use for silviculture, low intensity pasture and protected areas. Crops that can be successfully cultivated, if climate allows, include tea, rubber tree, oil palm, coffee and sugar cane.

Solonetz is a Reference Soil Group of the World Reference Base for Soil Resources (WRB). They have, within the upper 100 cm of the soil profile, a so-called "natric horizon". There is a subsurface horizon (subsoil), higher in clay content than the upper horizon, that has more than 15% exchangeable sodium. The name is based on the Russian соль. The Ukrainian folk word "solontsi" means salty soil. In Ukraine, many villages are called Solontsі.

<span class="mw-page-title-main">Gleysol</span> Saturated soil type

A gleysol or gley soil is a hydric soil that unless drained is saturated with groundwater for long enough to develop a characteristic gleyic colour pattern. The pattern is essentially made up of reddish, brownish, or yellowish colours at surfaces of soil particles and/or in the upper soil horizons mixed with greyish/blueish colours inside the peds and/or deeper in the soil. Gleysols are also known as Gleyzems, meadow soils, Aqu-suborders of Entisols, Inceptisols and Mollisols, or as groundwater soils and hydro-morphic soils.

<span class="mw-page-title-main">Stagnosol</span> Saturated soil type

A Stagnosol in the World Reference Base for Soil Resources (WRB) is soil with strong mottling of the soil profile due to redox processes caused by stagnating surface water.

A Technosol in the World Reference Base for Soil Resources is a Reference Soil Group that combines soils whose properties and pedogenesis are dominated by their technical origin. They contain either a significant amount of artefacts, some sort of geotechnical liner, or are sealed by technic hard material. They include soils from wastes, pavements with their underlying unconsolidated materials, soils with geomembranes and constructed soils in human-made materials. Transported natural soil material does not qualify as Technosol and is described with the Transportic qualifier in WRB. Technosols are often referred to as urban or mine soils. They are recognized in the new Russian soil classification system as Technogenic Superficial Formations.

<span class="mw-page-title-main">Andosol</span> Soils formed in volcanic ash and containing glass and amorphous colloidal materials

Andosols are soils found in volcanic areas formed in volcanic tephra. In some cases Andosols can also be found outside active volcanic areas. Andosols cover an estimated 1–2% of Earth's ice-free land surface. Andosols are a Reference Soil Group of the World Reference Base for Soil Resources (WRB). They are closely related to other types of soils such as Vitrosols, Vitrandosols, Vitrons and Pumice Soils that are used in different soil classification systems. The name comes from Japanese an and do, synonymous with kuroboku. In the USDA soil taxonomy (ST), many Andosols belong to the order of the Andisols. However, the definitions are different. Some Histosols (WRB) belong to the Andisols (ST), and some Andosols (WRB) belong to the Inceptisols (ST).

An anthrosol in the World Reference Base for Soil Resources (WRB) is a type of soil that has been formed or heavily modified due to long-term human activity, such as from irrigation, addition of organic waste or wet-field cultivation used to create paddy fields.

Kastanozem is one of the 32 Reference Soil Groups of the World Reference Base for Soil Resources (WRB). These soils are brighter than Chernozems, and are related to the Mollisols in the USDA soil taxonomy. They are rich in humus, and originally covered with early maturing native grasslands vegetation, which produces a characteristic brown surface layer in the first meter in depth. They have a relative high level of exchangeable calcium ions and sedoncary carbonates starting within 70 cm of the mineral soil surface.

Luvisols are a group of soils, comprising one of the 32 Reference Soil Groups in the international system of soil classification, the World Reference Base for Soil Resources (WRB). They are widespread, especially in temperate climates, and are generally fertile. Luvisols are widely used for agriculture.

A Retisol is a Reference Soil Group of the World Reference Base for Soil Resources (WRB). Retisols are characterized by clay migration and an additional specific feature: The clay-poorer and lighter coloured eluvial horizon intercalates netlike into the clay-richer more intensely coloured illuvial horizon. The illuvial horizon is the diagnostic argic horizon, and the intercalation is called retic properties.

References

  1. ↑ W.E.H. Blum, P. Schad, S. Nortcliff (2018). Essentials of soil science. Borntraeger Science Publishers, Stuttgart.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ↑ M. Whitney (1909). Soils of the United States. US Dept. Agric. Bur. Soil Bull. 55. Washington, D.C.
  3. ↑ Ad-hoc-AG Boden (2005). Bodenkundliche Kartieranleitung, 5. Auflage. Schweizerbart, Stuttgart.
  4. ↑ IUSS Working Group WRB (2022). "World Reference Base for Soil Resources, 4th edition". IUSS, Vienna.
  5. ↑ "Keys to Soil Taxonomy 2014". Archived from the original on 2018-11-28. Retrieved 2018-12-03.
  6. ↑ R.F. Isbell and the National Committee on Soil and Terrain (2016). "Australian Soil Classification, second edition (as Online Interactive Key)". CSIRO.
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