The central concept of
Aridisols is that of soils that are too dry for mesophytic plants to
grow. They have either:
(1) an aridic moisture regime and an ochric or anthropic epipedon
and one or more of the following with an upper boundry within 100 cm
of the soil surface: a calcic, cambic, gypsic, natric, petrocalcic
petrogypsic, or a salic horizon or a duripan or an argillic horizon, or
(2)A salic horizon and saturation with water within 100 cm of the
soil surface for one month or more in normal years.
An aridic moisture regime is one that in normal years has no
water available for plants for more than half the cumulative time
that the soil temperature at 50 cm below the surface is >5° C. and
has no period as long as 90 consecutive days when there is water
available for plants while the soil temperature at 50 cm is
continuously >8° C.