Rosek, M. 1994. Spatial and temporal soil water content changes within a sloping landscape. Dissertation, Michigan State University, East Lansing, Michigan, USA.
Soil physical properties and the amount of soil water within a sloping landscape are largely determined by landscape position. This study determined temporal dynamics of soil water within a sloping landscape by (1) examining the spatial variability of selected soil properties that regulate water retention; (2) quantifying water balance by slope position; (3) determining the minimum amount of stored soil water data required to estimate the amount of soil water within a sloping landscape using geostatistics. Neutron probe access tubes were placed at two meter intervals, in two transects, across a sloping topography of Kalamazoo loam (fine-loamy, mixed, mesic, Typic Hapludalfs) and Oshtemo sandy loam (coarse-loamy, mixed mesic, Typic Hapludalfs) at Kellogg Biological Station in southwestern Michigan. Volumetric water content of the soil was monitored approximately weekly in the spring, summer and autumn of 1990 and 1991 at 15, 30, 60, 90, 120, and 150 cm by neutron attenuation. Soil samples from a 48 by 34 meter grid between the access tubes were described and sampled. Water content of each sample point was estimated with CERES Maize for two sample dates. Selected volumetric water per 150 cm soil depth values were removed from the data sets, then kriged and cokriged for mm soil water at locations where data points were removed. The Ap horizon of the lower backslope, footslope, and toeslope display a greater mean thickness, percent silt and organic carbon, relative to upslope soils. The Bt l horizon and control-section display a greater mean silt and clay below the middle of the backslope. The amount of soil water was least within the upper backslope position, moderate within the summit and lower backslope positions, and greatest within the footslope and toeslope positions. Cokriging estimation of stored soil water, using mm soil water per 150 cm soil depth at field capacity as the auxiliary variable, reduced the required sample distance to twice the range of spatial dependence in the direction parallel to the contour of the slope. Variogram models of the amount of soil water from large data sets could be used to predict the amount of soil water in other studies with similar landscape and soil conditions.
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