How do Great Plains soils vary with rainfall and grass cover?

In the Great Plains, soil characteristics are closely correlated with rainfall patterns and the density of natural grass cover.1

• Humid Regions: Areas with higher rainfall and taller, heavier grass cover support the development of deep, black mollisols. These soils are rich in organic matter.1
• Semi-Arid Regions: As moisture levels decrease, the soils become progressively shallower, lighter in color, and contain less organic matter.1
• Arid Regions: In the driest parts of the plains, soils are the thinnest and least organic in composition.1

Across the region, most soils feature an accumulation of carbonates in their lower horizons, deposited by infiltrating water. As one moves from east to west, the climate becomes drier, resulting in a corresponding decrease in the depth of these carbonate accumulations. Additionally, the grassland ecosystem itself contributes to soil formation, typically creating a dark, nutrient-rich upper layer through the decomposition of grass litter, which distinguishes these soils from those found in forest or desert environments.12