Factors affecting soil thermal regime

Soil thermal properties include following aspects.

a. Specific heat capacity

• The change in heat of a unit bulk volume of soil per unit change in temperature is known as specific heat capacity of soil. Its unit is Cal/cm3/K or joule/cm3/0C.

b. Thermal conductivity of soil

• It is defined as the amount of heat transferred through a unit is of soil in unit time under a unit temperature gradient or it is the ability of a substance to transfer heat from molecule to molecule.
• Thermal conductivity of soil depends on the mineral and organic content of soil and volume fraction of air and water.
• Higher air content of soil has lower thermal conductivity, as thermal conductivity of air is much smaller than that of equal volume of solid or water.
• Since air and water content varies with time and space K also time variable and is function of soil depth because soil compaction is seldom uniform in depth but under normal condition temperature variation is ignored.

Unlike heat capacity, K is sensitive not only to the volume composition of soil but also to the size, space and spatial arrangement of soil particles.

c. Thermal diffusivity

• It is the rate at which a substance heats up as result of thermal gradients. It is also called as coefficient of thermal diffusion.
• It is also defined as the ratio of thermal conductivity to thermal heat capacity.