Modeling the Hysteretic Soil Water-Retention Capacity and Eliminating the Undesirable «Pump Effect»

A water-retention capacity of the soil is among its most important hydro-physical properties. It is formulated as dependence between the volume water content of soil and the capillary pressure of soil moisture. The study presents three models of a hysteresis of soil water-retention capacity. The identification of the parameters was carried out by means of a point approximation of an experimental data from the Mualem catalog on the main (boundary) drying and wetting branches of sandy soil using the computer program «Soil-Hysteresis» developed by the authors. A comparative analysis of hysteresis models is carried out on the basis of identifying significant differences between the errors of point approximation of experimental data using the Williams-Kloot test. The advantages of the models improved by introducing an additional additive parameter are revealed. Applying the condition of equality of the exponential parameter values for drying and wetting branches eliminates the undesirable (methodical) «pump effect». The use of physically based models of a hysteresis of a water-retention capacity has prospects in the development and application of resource-saving technologies in precision ameliorative agriculture and in the calculation of precise irrigation rates.