Heat Regime of Soil

the variation in the thermal state of the soil over time.

The primary source of the heat received by the soil is solar radiation. The thermal state of the soil is determined by heat transfer between the underlying rock, the soil, the vegetation, and the ground layer of air. The heat energy of the soil participates in the phase transitions of soil moisture, being liberated during freezing and condensation and being consumed during melting and evaporation. The amount of solar radiation arriving at the soil surface is lessened by vegetation; the cooling of the soil in winter is lessened by snow cover. The rate and direction of heat flow are determined by the magnitude and direction of the temperature gradients and by the soil’s heat capacity, heat conductivity, and temperature conductivity. The numerical values of these properties (effective values) depend on the soil’s moisture, density of structure, and granulometric (mechanical), mineralogical, and chemical composition.

The heat regime of the soil has a secular, multiyear, annual, and diurnal cyclicity, which is associated with alternation of insolation and radiation. Expressed as a multiyear average, the annual heat balance of any given soil is equal to zero; the average annual temperature is the same throughout the soil’s profile. Diurnal fluctuations in soil temperature affect the soil to depths of 20 cm to 1 m, and annual fluctuations to depths of 10 to 20 m. The heat regime of the soil is shaped primarily by climatic conditions. Nevertheless, it also has its own specific features, which stem from the thermophysical state of the soil itself and that of the underlying rock. Permafrost rock has a special impact on the soil’s heat regime.

The heat regime of the soil has a direct effect on the growth and development of vegetation. An important indicator of the heat supplied to plants by the soil is the sum of the active temperatures of the soil at a depth of 0.2 m, the depth of the arable layer. The heat regime of the soil is regulated by, among other methods, ridging, rolling, loosening, the density of seeding, shading, covering with strips of plastic and other materials, mulching, and artificial heating.