Variability of soil water tension and soil water content

Abstract

The objective of this study was the variability in soil water tension and in soil water content in a field soil. A transect was established with 91 positions, 1 m apart. Soil water content was measured 16 times at 0.3 m depth before and after flooding of the transect. Soil water tension was measured 13 times after flooding. Application of the “split moving-window” technique resulted in the detection of three boundaries partitioning the transect in four homogeneous segments. For each of these segments, the variability of soil water tension and water content significantly increased when the soil dried out. This experimental result confirmed the theoretical result obtained by Yeh, Gelhar and Gutjahr who used a stochastic model to predict the standard deviation in tension for moist soils, assuming unsaturated hydraulic conductivity is an exponential function of soil water tension. When the water content goes to zero in very dry soils, the variability in soil water content should decrease. However, data from this study and from the literature suggest that the variability in soil water tension in a dry soil remains more or less constant at a high level. The relationship between soil water content and tension was found to be linear for the investigated soil. Therefore, the variability of soil water tension and soil water content are quantitatively related by the slope of the soil water retention curve.