Effect of temperature on soil-water diffusivity

Abstract

Laboratory experiments were conducted to study temperature dependence of soil-water diffusivity and specific water capacity coefficients. Duplicate determinations of soil-water diffusivity, as a function of water content, were made at constant temperatures of 15, 25, and 35 °C on the same sample of Dundee silt loam. Diffusivity was determined by a one-step pressure-plate outflow method. Specific water capacity was computed from the slope of desorption curves obtained during the diffusivity measurements over the pressure head range of 0 to −0.66 bar. In general, diffusivity as a function of water content increased with increase in temperature. However, the effect of temperature was not large and probably can be neglected at normal field temperatures. Near saturation, it is difficult to interpret the thermal influence, for diffusivity approaches infinity and becomes indeterminate at saturation. Variations in soil-water diffusivity in low-swelling soils due to thermal effects can be explained on the basis of temperature dependence of surface tension and viscosity ratio. Specific water capacity of soil as a function of water content increased with increasing temperature with the largest response in the region of inflection of water content-pressure head desorption curves. Specific water capacity was essentially independent of temperature near saturation and low water contents.