Do Soil Water Measurements Reveal Multidimensional Flow Processes along Soil Catenae? ! # @ $.

In semi-arid agricultural fields, soil water is typically assumed to move vertically with no differential subsurface lateral flow.  In undulating terrain, such as our wheat field in eastern Colorado, dynamics of profile soil water can vary by landscape position in relation to terrain attributes, soil properties, and plant characteristics.  We used dielectric capacitance sensors to measure hourly water content over five years at 16 landscape positions and four depths in a field with alternating strips of winter wheat-fallow rotation. At summit and shoulder positions, profile soil-water dynamics may be explained by vertical infiltration, evapotranspiration and redistribution processes.  At downslope positions, complexities of overland flow and subsurface unsaturated lateral flow appear to influence soil water dynamics with depth. Rates of change in soil-water content at different depths and over multiple time scales were computed to illustrate the space-time dynamics. Crop water use accounts for most of the inter-strip variability, while soil hydraulic properties and near-surface hydrology affect the variability across landscape positions within each strip. Both short-term hydrology and long-term soil development influence the observed space-time patterns. Lateral flow processes and topographic convergence of flow paths affect the accumulation of soil water and associated dynamics at different measurement depths. We relate the space-time patterns in soil water content to terrain attributes, such as specific catchment area and slope. Feedbacks such as downslope nutrient transport, differential soil development, and plant water uptake variability along the soil catena must be considered to fully explain the space-time interactions.  Better understanding of such interactions should aid variable-rate management to enhance both production and sustainability of the soils.