Classes of Soil Temperature Regimes
Soli temprature
is measured by soil thermameter when the depth is specified because its
flactuates with the depth, usually 50cm is taken soli temp is depth dependent
Pergillic
When the soil is
permanenty frozen condition
Cryic (Gr. kryos,
coldness; meaning very cold soils)
Soils in this
temperature regime have a mean annual temperature lower than 8° C but do not
have permafrost.
In mineral soils
the mean summer soil temperature (June, July, and August in the Northern
Hemisphere and December, January, and February in the Southern Hemisphere)
either at a depth of 50 cm from the soil surface or at a densic, lithic, or
paralithic contact, whichever is shallower, is as follows:
If the soil is
not saturated with water during some part of the summer and
If there is no O
horizon: lower than 15° C; or
If there is an O
horizon: lower than 8° C; or
If the soil is
saturated with water during some part of the summer and
If there is no O
horizon: lower than 13° C; or
If there is an O
horizon or a histic epipedon: lower than 6° C.
In organic soils
the mean annual soil temperature is lower than 6° C.
Cryic soils that
have an aquic moisture regime commonly are churned by frost.
Isofrigid soils
could also have a cryic temperature regime. A few with organic materials in the
upper part are exceptions.
The concepts of
the soil temperature regimes described below are used in defining classes of
soils in the low categories.
Frigid
A soil with a
frigid temperature regime is warmer in summer than a soil with a cryic regime,
but its mean annual temperature is lower than 8° C and the difference between
mean summer (June, July, and August) and mean winter (December, January, and
February) soil temperatures is more than 6° C either at a depth of 50 cm from
the soil surface or at a densic, lithic, or paralithic contact, whichever is
shallower
Mesic
The mean annual
soil temperature is 8° C or higher but lower than 15° C, and the difference
between mean summer and mean winter soil temperatures is more than 6° C either
at a depth of 50 cm from the soil surface or at a densic, lithic, or paralithic
contact, whichever is shallower.
Thermic
The mean annual
soil temperature is 15° C or higher but lower than 22° C, and the difference
between mean summer and mean winter soil temperatures is more than 6° C either
at a depth of 50 cm from the soil surface or at a densic, lithic, or paralithic
contact, whichever is shallower.
Hyperthermic
The mean annual
soil temperature is 22° C or higher, and the difference between mean summer and
mean winter soil temperatures is more than 6° C either at a depth of 50 cm from
the soil surface or at a densic, lithic, or paralithic contact, whichever is
shallower. If the name of a soil temperature regime has the prefix iso, the
mean summer and mean winter soil temperatures differ by less than 6° C at a
depth of 50 cm or at a densic, lithic, or paralithic contact, whichever is
shallower.
Isofrigid
The mean annual
soil temperature is lower than 8° C. diffrence between MST and MWT is less then
5 (summer month are june, july, Agust and winter are Dec, Jan, Feb
Isomesic
The mean annual
soil temperature is 8° C or higher but lower than 15° C. diffrence between MST
and MWT is less then 5
Isothermic
The mean annual
soil temperature is 15° C or higher but lower than 22° C. and the diffrence
between MST and MWT is less then 5
Isohyperthermic
The mean annual
soil temperature is 22° C or higher. The diffrence between MST is MWT is less
then the 5
