- Ultisols
Ultisols are an order in
USDA soil taxonomy . They are defined as mineral soils which contain "nocalcareous material anywhere within the soil", have less than 10% weatherable minerals in the extreme top layer of soil, and have less the 35% base saturation throughout the soil.In the
FAO soil classification system, most Ultisols are known as "Acrisols". Others are classed as "Lixisols" or "Nitosols".The word "Ultisol" is derived from "ultimate", because Ultisols were seen as the ultimate product of continuous
weathering of minerals in a humid temperate climate without new soil formation viaglaciation .Typically Ultisols are red to yellow in color and are quite
acidic , often having apH of less than 5. The red and yellow colors result from the accumulation of iron oxide which is highly insoluble in water. Majornutrients , such ascalcium andpotassium , are typically deficient in Ultisols, which means they generally cannot be used for sedentary agriculture without the aid of lime and otherfertilizers such assuperphosphate . They can be easily exhausted, and require more careful management thanAlfisols orMollisols . However, they can be cultivated over a relatively wide range of moisture conditions.Ultisols can have a variety of clay minerals, but in many cases the dominant mineral is
kaolinite . This clay has goodbearing capacity and no shrink-swell property. Consequently, well-drained kaolinitic Ultisols such as the Cecil series are suitable for urban development.Ultisols are the dominant soils in the South of the
United States (where the Cecil series is most famous), southeasternChina ,southeast Asia and some other subtropical and tropical areas. Their northern limit (exceptfossil soils) is "very sharply" defined inNorth America by the limits of maximumglaciation during thePleistocene because Ultisols typically take "hundreds of thousands of years" to form - far longer than the length of aninterglacial period today.The oldest fossil Ultisols are known from the
Carboniferous period when forests first developed. Though known from far north of their present range as recently as theMiocene , Ultisols are surprisingly rare as fossils overall, since they would have been expected to be very common in the warmMesozoic andTertiary paleoclimates.In USDA soil taxonomy, Ultisols are divided into:
Aquults - Ultisols with a water table at or near the surface for much of the year
Humults - well-drained Ultisols that have high organic matter content
Udults - Ultisols of humid climates
Ustults - Ultisols of semiarid and subhumid climates
Xerults - temperate Ultisols with very dry summers and moist winters
References
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* cite web | url =http://soils.ag.uidaho.edu/soilorders/ultisols.htm | title =Ultisols| publisher =University of Idaho
accessdate =2006-05-14ee also
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Pedogenesis
*Pedology (soil study)
*Soil classification
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