Comparison of Soil Water Retention Functions for Humid Tropical Soils

The determination of soil hydraulic properties is of paramount importance as they are needed in many models of water and solute transport in soils, however conventional methods are quite difficult, expensive and sometimes cumbersome to use. Most studies of soil water retention functions are for temperate soils and their soil water retention curve (SWRC) cannot be extrapolated to tropical region, as such this study focused solemnly on SWRC of soils of tropical region (Malaysia and Indonesia to be specific). The analytical models of Brooks & Corey, van Genuchten and Kosugi were applied to model the SWRC for humid tropical soils, parameters of the three models were optimised by fitting them to 191 soil samples, of 10 different classes (International society of soil science classification) using VBA & MS excel solver add in. A comparison of the fitting capabilities and model quality was made using the sum of square of errors (SSQE) between observed and modelled values and, Akaike information criterion (AIC) respectively. The Kosugi model was found to describe the SWRC of the tropical soil samples better than the other models, as it has the lowest SSQE and AIC values.