A Model for Predicting Soil Thermal Diffusivity from Texture, Bulk Density, and Degree of Saturation at Room Temperature.

Soil thermal diffusivity (κ) is an essential parameter for studying heat transfer in soil. It is well understood that κ varies with soil texture, temperature, water content (θ), and bulk density (ρ_b), but few models are available for characterizing the changes. In this study, we developed an empirical model that estimated κ from soil particle size distribution, ρ_b and the degree of saturation (S_r), using existing soil thermal conductivity and heat capacity models. The model parameters were determined by fitting the model to κ(S_r) data from heat-pulse measurements on eight soils covering various textures and ρ_b. Independent evaluation with published κ(S_r) data showed that the new model described the κ(S_r) relationship accurately, with root mean square errors less than 0.70×10^-7 m² s^-1. The new model has potential applications in simulating heat conduction and predicting soil temperature dynamics under various field conditions.