Why is thermal diffusion important?
• How does thermal conductivity affect heat diffusion ? Direct absorption of solar radiation heats the soil surface, but the heating of the soil depths occurs because of thermal (heat) diffusion 1 downward into the soil profile. Heat flows from warm to cool at a rate determined by the thermal conductivity 1 of the material. The thermal conductivity of soil changes with its water content because soil pores can be either filled with air or water and water is a better conductor of heat than air. At midday, when solar heating of the soil surface is greatest, heat diffuses into the air above the soil and downward into the soil profile. At night, when the soil surface cools, heat diffuses upward to the soil surface. Temperature 3 fluctuations at the soil surface are much greater than deep in the soil because heat diffuses slowly through soil. For the same reason, the maximum and minimum temperatures at depth are delayed relative to the soil surface. Heat diffusion has biological significance
