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Ultisols an ochric epipedon and an argillic or kandic horizon that has few bases and commonly is calcium deficient. Most of these soils supported mixed coniferous and hardwood forest vegetation at the time of settlement. Some are now used as cropland or pasture.
Aquults are the Ultisols in wet areas where ground water is very close to the surface during part of each year, usually in winter and spring. They are on the coastal plains, particularly along the Atlantic Ocean and the Gulf of Mexico. Slopes are gentle. Most of the soils formerly supported forest vegetation. Many still support forest vegetation.
Humults are the more or less freely drained, humus-rich Ultisols. They are in Oregon and Washington and also occur in California and Puerto Rico. They commonly receive high rainfall but also have a moisture deficit during some season. The vegetation was mostly coniferous forest in the Northwest and rain forest in the tropics. Most of these soils are used as forest or have been cleared and are used as cropland or pasture.
Udults are the more or less freely drained, relatively humus poor Ultisols that have a udic moisture regime. They are in southern and eastern parts of the country. Most of these soils currently support or formerly supported mixed forest vegetation. Many have been cleared and are used as cropland, mostly with the use of soil amendments.
Ustults are the more or less freely drained Ultisols that have an ustic soil moisture regime and have a relatively low content of organic carbon. They occur in the extreme western part of the Ultisol delineation in Texas. Some are in California and on tropical islands. The vegetation is commonly forest or savanna. Some of the soils have been cleared and are used as cropland or pasture.
Xerults are the more or less freely drained Ultisols of Mediterranean climates. They are in California and Oregon. The vegetation formerly was and currently is mostly coniferous forest. Most of these soils are used as forest, but some have been cleared and are used as cropland or pasture.