VARIATION OF SOIL-WATER STORAGE ACROSS A SAND PLAIN HILLSLOPE

Although landscape variations in soil properties and productivity are often attributed to soil water conditions, landscape-scale studies of soil water are rare. This study describes variability of soil layering and soil water storage on a sand plain hillslope. According to a nested grid (with spacings from 2 to 16 m), soil cores were collected by horizon, and soil water profiles were measured with a neutron probe during the 1992 growing season. Particle-size analysis was conducted on the soil samples. A topographic survey of the hillslope was conducted, and elevation, slope, and slope curvature maps were constructed. Fine aeolian sand overlies medium sand of alluvial origin. The fine sand is thickest at upland positions, indicating the hill is a dune remnant. Lamellae only occur in the finer upland soils. Surface water storage (0-0.7-m interval) is greatest at the toeslope, where the epipedon is mollic. Subsurface storage (0.7-1.7-m interval) is greatest at upland positions, where perching of soil water is associated with lameIlae and the depositional discontinuity. Regression modeling showed that combinations of elevation (cubic trend), slope, and plan curvature explain 51 to 77% of the variability in profile water storage, depending on depth interval. When topographic trends are removed, spatial correlation of water storage only occurs within distances <6 m. Topographic trends can be used to model variability in soil water storage for this landscape, even though surface runoff is not significant.