Estimation of hydraulic properties of aggregated soils using a two-domain approach

Hydraulic properties of aggregated field soils estimated from limited data such as grain size distribution and bulk density show large deviations from experimental results. This paper presents an extension of Campbell's model for the estimation of these properties. This was achieved by considering the geometric mean diameter and the average bulk density of the aggregates. It is assumed that these soils are composed of two domains: the pore volume inside the aggregates and the pore volume between the aggregates (intra-and interaggregate pore spaces). Water was assumed to flow primarily from the two domains in sequence. This approach can be especially useful for mathematical modeling of solute movement during soil water drainage. The model was tested for three soil horizons with varying clay and humus contents. The soil water retention curves and the unsaturated hydraulic conductivities of these horizons were determined experimentally together with the dry bulk density and geometric mean diameter of the aggregates. The model shows acceptable agreement with the experimental data. Restrictions have to be made concerning the applicability of the model in wetting cycles, in frozen soils, and in the presence of transpiring vegetation.