Soils of grassland ecosystems.
Characterized by a thick, dark surface horizon.
The fertile surface horizon results from the long-term addition of organic matter derived from plant roots.
Mollisols occur primarily in the mid-latitudes and are extensive in the Great plains.
Among the most important and productive agricultural soils in the world.
Very deep soil formed in loamy and sand alluvium.
Have a water table at or near the surface most of the year.
Because of the high water table, grasses dominate.
The gray colors result from prolonged periods of saturation in which iron is reduced to colorless forms.
Southeastern South Dakota
Typical profile associated with soils formed under the grassland vegetation of the central Great plains.
The thick A horizon is more than a foot thick.
A result of the decomposition of roots.