Mollisols
Mollisols (from Latin mollis, "soft") are the soils of grassland ecosystems. They are characterized by a thick, dark surface horizon. This fertile surface horizon, known as a mollic epipedon, results from the long-term addition of organic materials derived from plant roots. Mollisols are among some of the most important and productive agricultural soils in the world and are extensively used for this purpose. They are divided into eight suborders: Albolls, Aquolls, Rendolls, Gelolls, Cryolls, Xerolls, Ustolls and Udolls.
Mollisols primarily occur in the middle latitudes and are extensive in prairie regions such as the Great Plains of the U.S. Globally, they occupy approximately 7.0% of the ice-free land area. In the U.S., they are the most extensive soil order, accounting for approximately 21.5% of the land area.
Aquolls
Mollisols with a water table at or near the surface for much of the year
Albolls, Rendolls
Albolls — wet Mollisols with a light-colored horizon formed through Fe reduction; Rendolls — shallow Mollisols over calcareous parent material
Gelolls, Cryolls
Gelolls — Mollisols of very cold climates (mean annual soil temperature <0°C); Cryolls — Mollisols of cold climates
Xerolls
Temperate Mollisols with very dry summers and moist winters
Ustolls
Mollisols of semiarid and subhumid climates
Udolls
Mollisols of humid climates