Aridisols are a soil order in USA soil taxonomy. Aridisols (from the Latin aridus, for “dry”) form in an arid or semi-arid climate. Aridisols dominate the deserts and xeric shrublands which occupy about one third of the Earth's land surface. Aridisols have a very poor concentration of organic matter (In this case decomposed material, humus). Water deficiency is the major defining characteristic of Aridisols. Also required is sufficient age to exhibit sub-soil weathering and development. Imperfect leaching in Aridisols often results in one or more subsurface soil horizons in which suspended or dissolved minerals have been deposited: silicate clays, sodium, calcium carbonate, gypsum or soluble salts. These subsoil horizons can also be cemented by carbonates, gypsum or silica. Accumulation of salts on the surface can result in salinization.
Aridisols are classified on the basis of their soil moisture regime (more specifically referenced to the soil moisture control section), which is dry in all parts >50% of the time in most years, and not moist for as much as 90 consecutive days when the soil is warm enough (>80C) for plant growth.
Aridisols occur on landscapes that are more than one million years old, a time scale that has allowed for development of accumulations of clay, carbonates, and silica.
The Aridisols are composed of 7 suborders distinguished by (i) soil temperature regime, and (c) occurrence of particular diagnostic horizons:
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