Spatial Analyses of Soil Properties, Terrain, and Water Dynamics In a Semi-Arid Agricultural Landscape.

Quantification of soil-water patterns in space and time is essential for understanding soil hydrological processes and to aid land management decisions. In undulating terrain, dynamics of profile soil water can vary by landscape position in relation to terrain attributes, soil properties, and plant characteristics.  A 56-ha instrumented watershed lies mostly within a dryland wheat field in eastern Colorado. Dielectric capacitance sensors were installed to estimate water content and to infer multi-temporal flux dynamics at 16 landscape positions and four depths. Soil cores were analyzed in the laboratory using multistep outflow measurements for soil hydraulic properties. These measurements combined with surface infiltration rates reveal complex patterns and geospatial scaling that affect soil water. At summit and shoulder positions, profile soil-water dynamics may be explained by vertical infiltration, evapotranspiration and redistribution processes. At downslope positions, complexities of infrequent overland flow events and temporally dampened subsurface unsaturated lateral flow appear to influence soil water dynamics with depth. Crop water use accounts for most of the variability between transects that are either cropped or fallow in alternating years, while soil hydraulic properties and near-surface hydrology affect the variability across landscape positions within each management zone. The data explored here will support simulations with process-based models to help identify dominant processes in space and time, including their scaling behavior, thresholds and likely feedbacks with agricultural management.