Scaling of near-saturated hydraulic conductivity measured using disc infiltrometers
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A function relating unsaturated soil hydraulic conductivity K and soil water pressure head h is most important for understanding water flow and chemical transport in the vadose zone. Furthermore, the K(h) function near saturation is critical for describing flow in macropores and other structural voids. The usefulness of similar media scaling and functional normalization to describe the near-saturated hydraulic conductivity function K(h) measured in situ at 296 spatial locations across a heterogeneous agricultural field was tested. Disc (ponded and tension) infiltrometers were used to measure K(h) at different field positions (corn row, no traffic interrow, and traffic interrow) cutting across different soil types (Nicollet and Clarion loam derived from glacial till material). The K(h) data ranged several orders of magnitude for different field positions and soil types and were found to be statistically different between different field positions. Using a Gardner type K(h) function, relative hydraulic conductivity values, and a hybrid of similar media scaling and functional normalization concepts, all disc infiltrometer data sets were coalesced to a single reference curve. Poor to moderately correlated K and h scale factors did not show any significant spatial structure across the field. A novel finding is that saturated hydraulic conductivities (K(sat)) could be successfully used as the scale factor for the near-saturated K(h) functions (e.g., 0-15 cm soil water tension) under all field positions and soil types at the experimental field.
