Soils

Soil moisture regimes are defined based on the watertable level and the presence or absence of available water (water that can be used by plants).  All moisture regimes, except aquic, are based on regional climate.  Aquic moisture regimes are based on the length of the period that the soil was saturated. 

Soil moisture regimes are used as a soil classification criterion because they affect soil genesis (formation), affect the use and management of soils, and can be used to group soils with similar properties and morphology.

The soil moisture regime classes include:

1. Aquic (or Perudic):  Saturated with water long enough to cause oxygen depletion.

2. Udic:  Humid or subhumid climate.

3. Ustic:  Semiarid climate.

4. Aridic (or Torric):  Arid climate.

5. Xeric:  Mediterranean climate (moist, cool winters and dry, warm summers)

In soil taxonomy, soil temperature regimes are based on mean annual soil temperatures.  Soil temperatures are taken at a depth of 50 cm from the soil surface, using the Celsius (centigrade) scale.  These regimes greatly affect the use and management of soils, particularly for the selection of adapted plants. The ten soil temperature regimes are cryic, frigid, hyperthermic, isofrigid, isohyperthermic, isomesic, isothermic, mesic, pergelic, and thermic.

The cryic soil temperature regime has mean annual soil temperatures of greater than 0 °C, but less than 8 °C, with a difference between mean summer and mean winter soil temperatures greater than 5 °C  at 50 cm, and cold summer temperatures.

The frigid soil temperature regime has mean annual soil temperatures of greater than 0 °C, but less than 8 °C, with a difference between mean summer and mean winter soil temperatures greater than 5 °C  at 50 cm below the surface, and warm summer temperatures. 

The hyperthermic soil temperature regime has mean annual soil temperatures of 22 °C or more and a difference between mean summer and mean winter soil temperatures...