Anisotropy of hydraulic properties of an Andisol in Southern Chile

Abstract

The hydraulic properties of the soil are determined by the changes in its structure. This work characterises the anisotropy depending upon the soil structure submitted to internal tension (-6 and -33 kPa) as a function of sampling orientation. A naturalised grassland located in Los Lagos soil series (Typic Durudand) was selected for the study. Undisturbed samples (250 cm3 cylinders) were collected at 5 and 20 cm depth in vertical (v) and horizontal (h) orientation. Soil hydraulic properties such as water retention curve (pF), saturated hydraulic conductivity (Ks ) and air permeability (ka ) were measured. The soil texture was loam, structure was granular in surface varying to subangular blocky in depth, and bulk density (Dap) was 0.7 g cm-3. Macroporosity (PDR: ϕ >50µm) at 20 cm showed a difference of 5% according to sampling orientation. Ks do not show differences at 5 cm, however, at 20 cm Ks -v values (3.27 log cm d-1) are almost one order of magnitude higher than Ks -h (2.78 log cm d-1). This behaviour is accentuated when comparing ka -v values (2.04 log µm2 ) with ka -h values (0.67 log µm2 ) evaluated at -6 kPa matric tension. The subangular blocks favour vertical preferential flows, which is reflected in the anisotropic behaviour of the hydraulic properties. At field capacity (-33 kPa), ka and C2 loose sensitivity to evaluate the anisotropic behaviour of the hydraulic properties of the soil.