Aridisols were one of the original ten orders of Soil Taxonomy. The orders in Soil Taxonomy are
based, as much as possible, on definable pedogenic profile characteristics. In addition the authors
tried to retain the great groups of the previous classification system. The Aridisol order is somewhat of
a compromise. It must not meet the requirements for: Gelisols, Histosols, Spodosols, Andisols, Oxisols
and Vertisols. In addition they can not have a mollic epipedon. The diagnostic horizons that are
criteria are mostly those that form in dry climates: calcic, gypsic, duripan, petrocalcic, petrogypsic, and
salic. The cambic horizons of Aridisols are mostly the result of translocation of carbonates and other
salts. The argillic horizons are mostly believed to be relict features.
An order for wet soils, gleyisols or aquisols, could have been proposed. These soils also have
diagnostic pedogenic properties. The authors did not choose to do so mainly based on the agricultural
use. They felt that most of these soils used as cropland would be drained and properties like an oxic
horizon, Vertic and Andic properties, and a mollic epipedon would have more lasting effect. In
addition relegating these soils to suborders helped preserved the pattern of broad areas of soil orders.
The choice may also have been influenced by the fact that the ""gleys"" were considered interzonel
soils in the previous classification system.
