6.11 - Soil Temperature Regimes
Soil temperature regimes worldwide map. (Images courtesy of the USDA-NRCS, edited by UNL)
Soil temperature regimes maps by continent. (Images courtesy of the USDA-NRCS, edited by UNL)
Soil Temperature Regimes: Descriptions
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 of less than 5 °C at 50 cm below the surface.
The isofrigid 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 of less than 5 °C at 50 cm. below the surface, and warm summer temperatures.
The isohyperthermic soil temperature regime has mean annual soil temperatures of 22 °C or more and a difference between mean summer and mean winter soil temperatures of less than 5 °C at 50 cm below the surface.
The isomesic soil temperature regime has a mean annual soil temperatures of 8 °C or more, but a difference between mean summer and mean winter soil temperatures of less than 5 °C at 50 cm below the surface.
The isothermic soil temperature regime that has mean annual soil temperatures of 15 °C or more but, 5 °C difference between mean summer and mean winter soil temperatures at 50 cm. below the surface.
The mesic soil temperature regime has mean annual soil temperatures of 8 °C or more, but less than 15 °C, and the difference between mean summer and mean winter soil temperatures is greater than 5 °C at 50 cm below the surface.
The pergelic soil temperature regime has mean annual soil temperatures of less than 0 °C at 50 cm below the surface. In this terperature regime, permafrost is present.
Thermic
The thermic soil temperature regime has mean annual soil temperatures of 15° C or more, but less than 22 °C; and a difference between mean summer and mean winter soil temperatures of greater than 5 °C at 50 cm below the surface.
| Soil Temperature Class | Temperature Range |
| Frigid | Lower than 8° C |
| Mesic | 8° C to 15° C |
| Thermic | 15° C to 22° C |
| Hyperthermic | 22° C or higher |
For soil families that have a difference of less than 5° C between the mean summer and mean winter soil temperatures, the soil temperature classes, defined in terms of the mean annaul soil temperature, are as follows:
| Soil Temperature Class | Temperature Range |
| Isofrigid | Lower than 8° C |
| Isomesic | 8° C to 15° C |
| Isothermic | 15° C to 22° C |
| Isohyperthermic | 22° C or higher |