A prairie is a vast stretch of open land covered in herbs, shrubs and grasses. Humans have contributed immensely to the shape of prairies. Fluctuation in climatic conditions, grazing animals and natural or man-made fires also reshaped and developed the ecology of the American prairie. Prairies are comprised of different types of soils.
Loess is a sediment of silt and clay. Glaciers reshaped lands as they retreated across North America and deposited silt as they melted. Strong winds carried large amounts of soil rich in silt from valleys near or around rivers and deposited them on nearby uplands, forming hill prairies. The Missouri Department of Conservation states that loess soils are aerated and well drained. The loess prairies also receive high sun exposure and wind speed, which is why most plants that grow here have waxy or small leaves to assist in water retention.
Glaciers altered the shape of the land as they retreated across North America. Large quantities of soil and rock that the glaciers carried were left behind by melting or melted ice, leading to the formation of glacial moraines. This is how sand prairies were formed on plains covered with sandy glacial outwash. The Michigan State University states that sand prairie soils is a mix of sandy and acidic soils called loam, with little organic matter and poor water retention capacity. This is why these soils are not conducive for agriculture, and the few plants that do grow in such soils are usually patchy, short and sparse.
Black soil is common in North American prairies. The soil is a rich and nutrient-dense mixture of silt, carbonate materials and clay, making it one of the most fertile and productive soils in the world. This soil exists under grasses in prairies in Midwestern states and the American West. The United States National Park Service states that the soil deposited by glaciers was exposed to a number of factors that eventually led to the formation of this type of soil, including extreme winters and summers, wildfires that caused the grass to burn and decompose and grazing animals that left their nitrogen-rich waste behind. This black, loamy, fertile soil was formed during thousands of years, and it gave settlers in the 19th century a lot of trouble plowing. A wide array of grasses grows on this fertile soil.