ESTIMATION OF HYDRAULIC-PROPERTIES OF AGGREGATED SOILS USING A 2-DOMAIN APPROACH

Hydraulic properties of aggregated field soils estimated from limited data such as grain size distribution and bulk density show large devia tions from experimental results. This paper presents an extension of C ampbell's model for the estimation of these properties. This was achie ved by considering the geometric mean diameter and the average bulk de nsity of the aggregates. It is assumed that these soils are composed o f two domains: the pore volume inside the aggregates and the pore volu me between the aggregates (intra-and interaggregate pore spaces). Wate r 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 s oil horizons with varying clay and humus contents. The soil water rete ntion curves and the unsaturated hydraulic conductivities of these hor izons were determined experimentally together with the dry bulk densit y and geometric mean diameter of the aggregates. The model shows accep table agreement with the experimental data. Restrictions have to be ma de concerning the applicability of the model in wetting cycles, in fro zen soils, and in the presence of transpiring vegetation.