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Vertisols of the world A more detailed map of the global distribution of Vertisols. A vertisol is a Soil Order in the USDA soil taxonomy [1] and a Reference Soil Group in the World Reference Base for Soil Resources (WRB). [2] It is also defined in many other soil classification systems. In the Australian Soil Classification it is called ...
Expansive clay, also called expansive soil, is a clay soil prone to large volume changes (swelling and shrinking) directly related to changes in water content. [1] Soils with a high content of expansive minerals can form deep cracks in drier seasons or years; such soils are called vertisols.
Due to the physical and chemical properties of some clays [4] (such as the Lias Group) large swelling occurs when water is absorbed. Conversely when the water dries up these clays contract (shrink). The presence of these clay minerals is what allows soils to have the capacity to shrink and swell.
Mollic epipedons also occur in some Andisols but the andic properties take precedence. In the World Reference Base for Soil Resources (WRB), Mollisols are split up into Chernozems, Kastanozems and Phaeozems. Shallow or gravelly Mollisols may belong to the Leptosols. Many Aquolls are Gleysols, Stagnosols or Planosols.
However, some ground-water gley soils have permeable lower horizons, including, for example, some sands in hollows within sand dune systems (known as slacks), and in some alluvial situations. Groundwater gleysoils develop where drainage is poor because the water table ( phreatic surface) is high, whilst surface-water gleying occurs when ...
The name comes from an Australian Aboriginal word meaning small water hole. [1] The pools are commonly a few metres across and less than 30 cm (12 in) deep but, in some instances, they may be several metres deep and up to 100 m (330 ft) across. Gilgais are found worldwide wherever there are cracking clay soils and marked wet and dry seasons. [1]
An Acrisol is a Reference Soil Group of the World Reference Base for Soil Resources (WRB). [1] It has a clay-rich subsoil. It is associated with humid, tropical climates, such as those found in Brazil, and often supports forested areas. [2]
A Retisol is a Reference Soil Group of the World Reference Base for Soil Resources (WRB). [1] 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.