Soil Temperature and Heat Flow

This chapter focuses on soil temperature. The value of soil temperature at any moment and the manner of its variation in time and space are of primary importance. They help determine the rates and directions of soil physical processes and of energy and mass exchange with the atmosphere. Soil temperature varies in response to changes in the radiant, thermal, and latent energy exchange processes that take place primarily through the soil surface. The effects of these phenomena are propagated into the soil profile by a complex series of transport processes, the rates of which are affected by time-variable and space-variable soil properties. Hence, the quantitative formulation and prediction of the soil thermal regime become a formidable task. Even beyond passive prediction, the possibility of actively controlling or modifying the thermal regime requires the knowledge of the processes at play and of the environmental and soil parameters that determine their rates. The pertinent soil parameters include the specific heat capacity, thermal conductivity, and thermal diffusivity (all of which are strongly affected by bulk density and wetness) as well as the internal sources and sinks of heat operating at any time.