Functional Description of Water-Retention Capacity and Relative Hydraulic Conductivity of the Soil Taking into Account Hysteresis

The aim of this study is to model the water-retention capacity and the relative hydraulic conductivity of the soil as a capillary-porous medium, as well as to verify the proposed models in comparison with the well-known world analogues. This aim is achieved by solving the following tasks: (1) description of the soil hydrophysical properties in the form of three systems of functions with corresponding sets of common parameters, (2) verification of these systems by evaluating the relative hydraulic conductivity and scanning branches of the water-retention capacity using parameters identified from the literature data on the main branches of the water-retention capacity hysteresis for the 3501 Rubicon sandy loam; (3) application of the equality of exponential parameter values in the calculations of the drying and wetting branches of hysteresis loop to eliminate the artificial “pump effect”; (4) study of the influence of the additive parameter on the errors of the point approximation of data on the main branches of the water-retention capacity, as well as on the errors of estimating the relative hydraulic conductivity and scanning branches of the water-retention capacity hysteresis; and (5) identification of significant differences between the errors of these estimates according to the Williams–Kloot criterion for choosing the best system of functions. Application of the proposed models seems to be preferable for solving the problems of irrigation farming, such as forecasting the water availability of crops and calculating precision irrigation rates.