Generalized Soil Water Retention Equation for Adsorption and Capillarity
AbstractA new soil water retention curve (SWRC) equation, generalized from previous models and the latest understanding of soil water interaction, explicitly accounts for capillary and adsorptive processes. Under the assumption of local thermodynamic energy equilibrium, soil water is one of two types (capillary and adsorptive) and occurs in three retention regimes in the order from high to low matric potential: Capillary, adsorbed film, and tightly adsorbed soil water. A new equation for adsorptive water as a function of matric potential is introduced. The transition between adsorption and capillary regimes is smoothly described with a cavitation probability function imposed on a commonly used SWRC model. Three parameters (adsorption capacity, adsorption strength, and mean cavitation suction) are defined, replacing the commonly used parameters of residual moisture content, pore structure, and residual suction. The soil water retention data for 21 soils, representing a variety of soil compositions, are us.