EFFECT OF BULK DENSITY ON HYDRAULIC PROPERTIES OF HOMOGENIZED AND STRUCTURED SOILS

In order to determine the effect of bulk density and soil structure on their hydraulic behaviour, undisturbed samples were collected and disturbed samples were prepared from a Luvisol. The experimental field, located in Harste/Goettingen, Germany, was cultivated with sugar beet (Beta vulgaris). The water retention curve (WRC) and saturated hydraulic conductivity (Ks) were measured on undisturbed samples and homogenized samples prepared at different bulk densities (1.2 -1.4 and 1.6 Mg m-3). To determine the effect of soil shrinkage on the unsaturated hydraulic conductivity (k/ψ), the vertical deformation of the repacked samples was measured and relative water content differences (dθ)were determined. The hydraulic properties of soils with identical texture depend on bulk density (dB) and structure. The increasing bulk density not only induces changes in the pore-size distribution but also affects the ability of soil to shrink and to conduct water under unsaturated conditions. Greater shrinkage was observed for samples with lower dB as a consequence of reduction of coarse pores. The water content differences increase with decreasing bulk density, inducing an increasing error in the estimation of k/ ψ.