THE APPLICATION OF DIFFUSION-MODELS TO AN AGGREGATED SOIL

In models on diffusive transport it is necessary to make use of a simplifying description of the geometry of an aggregated soil. It is proposed to use a (hypothetical) model soil consisting of spherical, cylindrical, or flat aggregates. The model aggregates are of different sizes, and each size class occupies a certain fraction of the total volume. These volume fractions can be calculated in such a way that diffusive transports take place in approximately the same way in soil and model soil. The method is operational. The quantity to be measured is the shortest distance from a randomly chosen point to the inter-aggregate space. The desired volume fractions can be derived from the probability distribution of this distance. The procedure does not require the existence of individual aggregates and may be applied, for instance, to a cracked clay soil. The use of a simple model soil is based on the shape independence of diffusion processes. That shape independence has been verified by means of theoretical calculations for both a single aggregate and an aggregated soil. © 1990 Williams and Wilkins.