A physically based model for the entire soil water retention curve

Abstract

An adequate description of the water retention curve (WRC) is an urgent hydrophysical problem in connection with computer modeling of water and solutes transport in soils and landscapes. The study presents a physically based thermodynamic model for describing soil water retention in the complete moisture range from saturation to oven drying. Unlike well-known empirical analogues, the new model is obtained on the basis of the equations of capillarity and disjoining water pressure as the main mechanisms of soil water retention, along with their limitations by porosity, the maximum height of capillary rise, and the standard soil water potential at a conditionally zero water content (the oven dryness state). Validation of the model using the author's own and literature WRC data for soils with various textures from sands to clays confirmed its good approximation ability with R² = 0.984–0.999 and normalized root mean squared errors 2–20 times lower than in the commonly used van Genuchten model with the same number of parameters. In addition to describing the WRC with calculating pore size distribution, the new model estimates the generalized Hamaker constant for molecular interfacial interactions and the specific soil surface area alternatively to the standard Brunauer–Emmett–Teller (BET) method.