According to the USDA Soil Taxonomy, mollisols are neutral to slightly acidic soils of temperate latitudes that are covered with grasses (Poaceae). They are found in the Argentinean pampas, the prairies of the Midwest of the USA and the steppes of a broad band stretching from Southeastern Europe to Central Asia, as well as in China.
Mollisols usually show a well-developed soil profile. At the surface is the dark A horizon, up to one metre deep, which is black in colour due to the high humus content and is constantly renewed, for example by dead plant roots. Below this lies the B horizon, which is enriched with calcium carbonate, especially in dry regions.
Mollisols contain numerous minerals such as magnesium, calcium, potassium and sodium in a form that is available to plants, making mollisols exceptionally good soils for agricultural use. In particular, cereals such as wheat thrive especially well on mollisols.
In addition, mollisols are also an important habitat for numerous animals, such as earthworms, ants, termites or even moles or prairie dogs.
Some mollisols form from the deposition of loess; if the plant cover is removed, they are particularly susceptible to erosion, as seen in what is now known as the Dust Bowl region of the Midwestern United States or in northern China.
Worldwide, about 9 million square kilometers or 7 percent of the ice-free land area is covered with mollisols.
A distinction is made between 8 suborders:
- Soil Survey Staff: Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys. 2nd edition. Natural Resources Conservation Service. U.S. Department of Agriculture Handbook 436. Washington D.C., USA, 1999.
- Soil Survey Staff: Keys to Soil Taxonomy. 12th edition. Natural Resources Conservation Service. U.S. Department of Agriculture. Washington D.C., USA, 2014.