Soil is made up of weathered materials, such as water, oxygen and organic matter. There are a wide range of soil types in the United States. “Soil Taxonomy,” a publication by the United States Depart of Agriculture (USDA), classifies American soils into 12 distinct groups called orders. Published in 1975, “Soil Taxonomy” is not only widely used in America, but it is used worldwide. According to the University of Idaho, these soil orders include oxisols, mollisols, aridisols, spodosols, utisols, vertisols, histosos, gerisols, andisols, entisols, inceptisols and alfisols.
Mollisols are found in grasslands and are known for their dark, thick surface horizon. The term “mollic epipedon” describes the surface horizon of this soil, which is fertile because of adding organic materials that come from plant roots. Mollisols mostly come from middle latitudes and prairie areas, including the Great Plains. It’s the most extensive soil in the United States, accounting for roughly 21.5 percent of the land, according to the University of Idaho.
Oxisols, found mostly in tropical and subtropical areas, are rich in iron and al oxide minerals, according to the University of Idaho. These soils are highly weathered and occupy only 0.02 percent of land area, restricted to Hawaii. They have a low fertility because of their extremely low nutrient reserves and high phosphorous content from oxide minerals.
Aridisols are soils thought to have almost no vegetation, but this is not true, according to the University of Missouri. This soil is found in arid desert regions. Plants that grow in this soil include cacti, yucca, mesquite trees, agave and others that are suited for harsh, dry conditions. Aridisols are commonly used as rangeland in the Southwest.
Spodosols are composed of spodic materials that have many amorphous combinations of organic materials and aluminum, either with or without iron. They’re mostly found in the Northeast, southern Alaska, the Great Lake states, as well as high altitudes of the Northwest, notes the USDA. These soils are naturally infertile, although they can be productive when properly managed.
Utisols are mostly located in forests, with large areas of them in the Southeast. These soils can be useful in supporting forested ecosystems, notes the University of Missouri. They’re also used for pasture or row-crop agriculture. Using utisols for agronomic purposes requires fertilizer and liming because these soils are acidic and have low nutrients.
Vertisols contain heavy clay that signifies a soil with considerable expansion and contractions caused by either a presence or deficiency of moisture, notes Physical Geography. These soils are located mostly in regions that have much precipitation. They are mainly found in Texas where they’re used in growing cotton.
Histosols are basically made of organic matter and typically form in wetland settings where there’s restricted drainage, which hinders plant and animal remains from decomposing. This causes organic materials to accumulate, resulting in histosols becoming important to ecology because of the large amounts of carbon they contain. In the United States, histosols make up roughly 1.6 percent of the land, according to the University of Missouri. Histosols are often called peats and mulches because they have physical properties that limit their use for engineering purposes.