Vertisols are clay-rich soils that shrink and swell with changes in moisture content. During dry periods, the soil volume shrinks, and deep wide cracks form. The soil volume then expands as it wets up. This shrink/swell action creates serious engineering problems and generally prevents formation of distinct, well-developed horizons in these soils. In areas where Vertisols are extensive, they are known by local names, such as cracking clays (Australia), Adobe (Philippines), Shachiang (China), Black Cotton soils (India), and Vleigrond (South Africa), as examples.
The clay content of Vertisols is generally 50 - 70 percent and a relatively high proprotion is fine clay.
Globally, Vertisols occupy ~2.4% of the ice-free land area. In the US, they ccupy ~2.0% of the land area and occur primarily in Texas.
Aquerts - Vertisols with a water table at or near the surface for much of the year but are also dry enough for periods for cracks to open. Typically in low areas such as glacial lake plains, flood plains, stream terraces, and depressions.
Cryerts - Vertisols of cold climates. Previous definitions limited their extent to warmer climates, but fine textured soils in cold temperature regimes periodically shrink and swell forming cracks that commonly open in late summer. Cryerts occur on the cold prairies of Canada where they are commonly derived from lacustrine deposits. They also occur in the US Rocky Mountains.
Xererts - temperate Vertisols with very dry summers and moist winters of the Mediterranean climates. These soils have cracks that regularly close and open each year. In the US, most of the soils supported grasses.
Torrerts - Vertisols of dry climates. Cracks may stay open for most of the year and close for a few days in most years. Many of these soils dot the landscape in closed depressions that may be ponded from time to time by runoff from higher areas. Torrents that are more continuous are typically underlain by parent materials that tend to weather the smectictic clays such as basalt. Torrents are further subdivided by presence or absence of salts. Torrents in the US occur mostly in the southwest and a few occur in Hawaii. Commonly used for rangeland.
Usterts - Vertisols of semiarid and subhumid climates. Cracks open and close once or twice during the year. Extensive in Texas, on the Great Plains, in Australia, in Africa south of the Sahara, and in India. Many of these soils formed in gentle sloping areas. If irrigated, Usterts are used intensively, but large areas are used for grazing due to a lack of machinery to till soils.
Uderts - Vertisols of humid climates. The cracks may not open completely some years due to high precipitation. In the US, the soils occur on gentle slopes and are derived dominantly from marine shales, marls, and alluvium. Many of these soils suppored grass, but some support a hardwood or pine forest.