When grasses die back in the winter, the leaves and roots remain. This is like mulching a garden, and generates soils very rich in organic matter and materials. The vast temperate grasslands have soils that are rich, and deep. Because of this, prairie soils are the breadbasket of the world! They produce a majority of the wheat, corn, and soybean production in the US (and the world). This is responsible for cooking oils, dog foods, work gloves, diapers, cat litter, soymilk, and a whole host of products that we use every day!
These temperate grasslands have cold winters, and warm summers, and have medium to low precipitation. They form in areas that are too dry to be forested, but too wet to be desert.
Most of the prairie soils are called Mollisols (latin for soft), because of their deep, dark layer of topsoil. The prairie is divided into three major regions. Tall grass (taller than 50 cm) in the east, and short grass (up to 50 cm tall) in the West, with mixed grass in the middle. The taller the grasses, the more organic matter that is created, the darker and deeper the soils are.
These rich grasslands have many different kinds of organisms that call it home. Flowers, ranging herds of bison, wild horses, wolves, and prairie dogs are just some examples.
Relief and Parent Materials
Have you ever heard the expression "Kansas is flatter than a Pancake!" The prairies can be very flat, to rolling hills, depending on where you are located at. Most of the soils, especially in North America, come from windblown silt called loess. In the north, the loess is on top of glacial sediments, and in the south, it is over river and old ocean sediments.
In areas like Texas in the South, soils are much older than in the North, which were covered with glaciers until about 10-15,000 years ago.
Special Issues on the Prairie
A natural prairie recycles its nutrients. When plant and animals die, they decompose and provide nutrients to the next set of plants and animals. We rely on these prairie soils for our foods. Producing foods can be very difficult on the soils. Like mining, soil nutrients are taken up in the plants are taken away to be fed to organisms in cities halfway across the country. This means that farmers need to fertilze their soils to continue to provide health and fertility. Some farmers compost, and others buy fertilizer from the stores.
The western short grass prairie is commonly used for grazing, and can be overgrazed. This can lead to erosion problems, and loss of productivity, including desertification.
Where are these Soils?
Before settlement, grassland covered about half of the lower 48. Most of the prairie (95%) is located west of the Mississippi, with Illinois being the only state east of the Mississippi with substatial acreage. Only 13% were the tall grass prairies.
For more information on the desert, including downloadable PowerPoints, assessment questions, and educational links, please visit the SCOOP! Teachers Guide.