Measuring the hydraulic properties of a stable aggregated soil

Abstract

Reliable modelling of soil-water flow requires accurate and convenient measurement of the appropriate soil hydraulic properties, which can be particularly problematic in structured soils with a distinct macropore-matrix dichotomy in the flow regime. In this paper the hydraulic properties of an aggregated soil at water supply potentials, Ψ 0, near saturation are obtained using the disc permeameter. The sorptivity, S, the hydraulic conductivity, K( ϑ), and the wetting soil-water characteristic, Ψ(ϑ), are measured directly. The soil-water diffusivity, D( ϑ), is derived from measurements of K( ϑ) and Ψ(ϑ) and is also shown to be well described by deconvoluting the sorptivity using the Parlange approximation. This description of D( ϑ) conveniently supplements estimates obtained over a wider range of water contents using the absorption method of Bruce and Klute, with water content profiles obtained by gamma scanning. Finally, the measured K( ϑ) function is accurately described by introduction of a method for scaling Ψ(ϑ) over the inter- and intra-aggregate flow regions and matching to the measured hydraulic conductivity at two points.