PREDICTING THE WATER-RETENTION CURVE FROM PARTICLE-SIZE DISTRIBUTION

Abstract

We present a simple model for predicting the water-retention characteristics of sandy soils from routinely available textural and structural soil properties. Using the basic concept of shape similarity between the retention curve h(θ) and the cumulative particle-size distribution function F(d), we derive an analytical expression for h(θ), following the well-known Brooks and Corey equation and taking into account air entrapment and hysteresis. Except for the water content at natural saturation, which is used as an independent input parameter, the operation parameters of the model are obtained directly from F(d) and dry bulk density. The results obtained for 10 sandy soils available from laboratory and field experiments show an excellent agreement between predicted and experimental h(θ) curves. The errors introduced by the prediction model are of the same order of magnitude as the experimental errors of h(θ). In this paper we consider only sandy soils without organic materia. In a subsequent paper we will extend the analysis to more general soils.