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Alfisols are extensive in the United States. They make up about 13.9 percent of the surface area. In normal years water they are dry when the soils are warm enough for plants to grow.
Aqualfs, which have warm and aquic conditions, primarily are found in an area bordering the southern part of the Mississippi River, in southern Illinois, and in Indiana and Ohio. Most Aqualfs have some artificial drainage or other water control and are used as cropland for corn, soybeans, and rice. Nearly all Aqualfs are believed to have supported forest vegetation in the past.
Cryalfs, which are the cold Alfisols, occur mostly at high elevations, mainly in the Rocky Mountains in the Western United States. Most of the Cryalfs in the United States are used as forest because of their short, cool growing season.
Udalfs, which have a udic moisture regime, are of large extent in the United States. They form a belt extending from Minnesota through Wisconsin, Michigan, Indiana, and Ohio and ending in New York State. Another large area of Udalfs begins in southern Iowa and extends through Missouri, Illinois, and the States to the south bordering the Mississippi River. All Udalfs are believed to have supported forest vegetation at some time during development.
Ustalfs, which have an ustic soil moisture regime, occur on the southern Great Plains, mostly in Texas and Oklahoma. They also occur throughout the Rocky Mountain States from Montana to Arizona and New Mexico and in the Black Hills of South Dakota. The dry season is pronounced. Many Ustalfs support savanna vegetation, and some supported grassland vegetation. Most are used as cropland or grazing land.
Xeralfs, which have a xeric soil moisture regime, are mostly in California, but small areas are in Oregon, Washington, Idaho, and Utah. The natural vegetation was a mixture of annual grasses, forbs, and woody shrubs on the warmest and driest Xeralfs and coniferous forest on the coolest and most moist Xeralfs. Xeralfs are used mostly as cropland, forest, or grazing land. Small grains, mostly winter wheat, are the most common crops..