Equation 2 assumes that C 1 is constant with depth in the soil. For a unit surface area, the rate of change in heat storage within the soil layer is expressed as . For a unit surface area, the rate of change in heat storage within the soil is also equal to the change in heat flux density through the soil layer . Therefore, k is useful to determine the rate of temperature change of a soil layer. Recall that k is directly proportional to C 1 and inversely proportional to C v .
C v continues to increase even when the soil is relatively wet.
Consequently, for a dry soil, k increases with water content, but it slows and sometimes decreases when the soil nears saturation. As a result, the maximum change in temperature with time will occur at a water content below saturation. W m -2 and the soil is warming Accounting for the change in soil heat storage is important for estimating G at the surface. The soil was a Yolo clay loam soil that was irrigated once per week. 20.8 o C are measured on either side of the heat flux plate.