DIFFUSION WITHIN SOIL MICROSTRUCTURE A STRUCTURAL PARAMETER FOR SOILS

Abstract

Summary To estimate the diffusion coefficient of gases, D c , within soil crumbs gaseous diffusion was measured first on a packing of dry 1–2 mm crumbs, then again after the crumb pores, but not the inter‐crumb pores, had been rendered nonconducting by saturating with an inert liquid. Using equations for analogous electrical properties of heterogeneous materials, the range of values of D c /D o was from 0.025 to 0.156 for eight soils with crumb porosities in the range 0.25 to 0.41. For each soil, single value parameters for soil complexity were calculated from D c /D o and the appropriate crumb porosity, and these were in accord with known behaviour in the field: the better the structure, the smaller is the complexity parameter. The validity of the method was checked by measuring the diffusion coefficient, D , by standard methods on blocks of soil and also by the indirect method on crumbs obtained by crushing the block. Comparison of these values for D and D c , ideally the same, confirmed the adequacy of the method.