There are five general soil moisture regimes: aquic, udic, xeric, ustic, and aridic. These moisture regimes have detailed definitions (Soil Survey Staff 1999). General working definitions are ...

Both soils have mean annual precipitation of 450 mm. The Ustoll (a) has an ustic soil moisture regime and the Xeroll (b) has a xeric soil moisture regime. Note the presence of calcium carbonate ...