Parameters of the Thermal Diffusivity vs. Water Content Function for Mineral Soils of Different Textural Classes

Abstract

This work provides parameters of the soil thermal diffusivity vs. water content function for eight textural classes. The experimental thermal diffusivity vs. water content curves previously obtained for mineral soils of the European Russia were used. In the course of the study, the dataset for 77 undisturbed soil samples was analyzed. This dataset included loose sand, dense sand, sandy loam, light loam, medium loam, heavy loam, light clay, and medium clay. Thermal diffusivity of soil samples measured using the unsteady-state method varied within the dataset from 0.77 × 10–7 to 10.09 × 10–7 m2/s. To parameterize the soil thermal diffusivity vs. water content dependences the grouping method was applied. Soils were grouped according to textural classes using the classification either after Dolgov or after Kachinskii. For each of the chosen textural classes, the parameters of an average thermal diffusivity vs. water content curve were estimated from all the experimental data points for this class by approximating these points with the previously suggested four-parameter function. The approximation accuracy was estimated using Willmott’s index of agreement between the model-predicted curve and the observed values. The greatest value for the index of agreement (0.845) was obtained for the medium clays defined according to Dolgov and the smallest one (0.532) for sandy loams. The index of agreement for the whole dataset was 0.699 when the textural classes were defined according to Dolgov, and 0.688 when they were defined according to Kachinskii. In addition, the parameters of an average general curve for the whole experimental dataset were obtained. The index of agreement between this general curve and observed values was only 0.554, which confirms the efficiency of soil grouping by textural classes.