Determination of Soil Sorptive Potential by Soil Water Isotherm

Soil sorptive potential (SSP) has recently been conceptualized as the sum of four known electromagnetic potentials in soil: cation and surface hydration, van der Waals attraction, electrical attraction, and osmosis due to electrical double layer. The SSP is most pronounced near the soil particle or intracrystalline surface and rapidly decays with increasing distance therefrom, governing the highly spatially varying characteristics of many fundamental soil properties such as pore water pressure, soil water density (SWD), and soil water phase transition. A novel framework was developed to determine the functions of SSP and SWD, directly using the experimental soil water isotherm (SWI) data with the aid of closed-form SWI and SWD models. A wide spectrum of soil types was examined to validate the proposed framework. Results indicate that the SSP in these soils can vary up to six orders of magnitude within the first three layers of adsorbed water molecules, leading to abnormally high values in both water pressure (∼103 MPa) and SWD (1.26 g/cm3) at the soil–water interface. The predicted SWD curves are comparable to the existing experimental SWD measurements, and the controlling parameters for the SSP calibrated by the predicted SSP curves also show good agreement with the values reported in the literature, all confirming the validity of the proposed framework. It is concluded that soil sorptive potential and soil water density functions can be reliably determined from soil water isotherm data.