Oxisols are a soil order in USDA soil taxonomy, best known for their occurrence in tropical rain forest within 25 degrees north and south of the Equator. In the World Reference Base for Soil Resources (WRB), they belong mainly to the ferralsols, but some are plinthosols or nitisols. Some oxisols have been previously classified as laterite 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.
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. The natural vegetation of vertisols is grassland, savanna, or grassy woodland. The heavy texture and unstable behaviour of the soil makes it difficult for many tree species to grow, and forest is uncommon.
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.
Entisols are soils, as defined under USDA soil taxonomy, that do not show any profile development other than an A-horizon. Entisols have no diagnostic horizons, and are unaltered from their parent material, which could be unconsolidated sediment, or rock. Entisols are the most common soils, occupying about 16% of the global ice-free land area.
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).
In soil classification, an Umbrisol is a soil with a dark topsoil and in which organic matter has accumulated within the mineral surface soil—in most cases with low base saturation—to the extent that it significantly affects the behaviour and utilization of the soil. Umbrisols are the counterpart of comparable soils with a high base saturation.
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).
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.
A Leptosol in the World Reference Base for Soil Resources (WRB) is a very shallow soil over continuous rock or a deeper soil that is extremely rich in coarse fragments. Leptosols cover approximately 1.7 billion hectares of the Earth's surface. They are found from the tropics to the cold polar regions and from sea level to the highest peaks. Leptosols are particularly widespread in mountain areas, notably in Asia, South America, northern Canada and Alaska; and in the Saharan and Arabian deserts. Elsewhere, Leptosols can be found on hard rocks or where erosion has kept pace with soil formation or removed the top of the soil. In the FAO soil classification for the FAO/UNESCO Soil Map of the World (1974) the Leptosols on calcareous rock were called Rendzinas, those on acid rock were Rankers. The very shallow, less than 10 cm deep, Lithic Leptosols in mountain regions are the most extensive Leptosols on Earth.
A Calcisol in the World Reference Base for Soil Resources (WRB) is a soil with a substantial secondary accumulation of lime. Calcisols are common in calcareous parent materials and widespread in arid and semi-arid environments. Formerly Calcisols were internationally known as Desert soils and Takyrs.
A Cambisol in the World Reference Base for Soil Resources (WRB) is a soil in the beginning of soil formation. The horizon differentiation is weak. This is evident from weak, mostly brownish discolouration and/or structure formation in the soil profile.
A Durisol is a Reference Soil Group under the World Reference Base for Soil Resources (WRB) referring to free-draining soils in arid and semi-arid environments that contain grains cemented together by secondary silica (SiO2) in the upper metre of soil, occurring either as concretions (durinodes – duric horizon) or as a continuously cemented layer (duripan – hardpan (Australia) – dorbank (South Africa) – petroduric horizon). The name is derived from Latin durus for hard.
A Planosol in the World Reference Base for Soil Resources is a soil with a light-coloured, coarse-textured, surface horizon that shows signs of periodic water stagnation and abruptly overlies a dense, slowly permeable subsoil with significantly more clay than the surface horizon. In the US Soil Classification of 1938 used the name Planosols, whereas its successor, the USDA soil taxonomy, includes most Planosols in the Great Groups Albaqualfs, Albaquults and Argialbolls.
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.
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).
A fluvisol in the World Reference Base for Soil Resources (WRB) is a genetically young soil in alluvial deposits. Apart from river sediments, they also occur in lacustrine and marine deposits. Fluvisols correlate with fluvents and fluvaquents of the USDA soil taxonomy. The good natural fertility of most fluvisols and their attractive dwelling sites on river levees and higher parts in marine landscapes were recognized in prehistoric times.
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.
Nitisol, in the World Reference Base for Soil Resources (WRB), is a deep, red, well-drained soil with a clay content of at least 30% and a polyhedral structure or a blocky structure, breaking into a polyhedral or a flat-edged structure. The soil aggregates show pressure faces. Nitisols correlate with the kandic alfisols, ultisols and inceptisols of the USDA soil taxonomy.
