Modeling and Prediction of Soil Water Vapor Sorption Isotherms.

Soil water vapor sorption isotherms describe the relationship between water activity (a_w) and moisture content along adsorption and desorption paths. The isotherms are important for modeling numerous soil processes and are also used to estimate several soil (specific surface area, clay content, cation exchange capacity) and engineering properties (e.g. swelling potential). Our objectives for this work were to: (i) evaluate the potential of several theoretical and empirical isotherm models to accurately describe measured moisture adsorption/desorption isotherms (a_w range of 0.03 to 0.93) for a wide range of soils; and (ii) develop and test regression models for estimating the isotherms from clay content. Preliminary results show reasonable fits of the majority of the investigated empirical and theoretical models to the measured data although some models were not capable to fit both sorption directions accurately. Evaluation of the developed prediction equations showed good estimation of the sorption/desorption isotherms for tested soils.