Temporal variations in soil hydraulic properties due to biological activity are not well understood. Plant root growth and subsequent decay creates flow channels, promotes soil aggregation, and changes the pore-size distribution. The purpose of this study is to quantify the changes in the soil unsaturated hydraulic conductivity K(&Theta) and moisture retention &Theta(h) functions during development and decay of a native grass (Blue grama (Bouteloua gracilis)) root system. The grass was grown in the greenhouse in re-packed sandy loam contained in 15 cm dia. by 15 cm deep PVC columns. Soil hydraulic functions were measured at several elapsed times using a continuous flow method in combination with inverse numerical analysis of Richards' equation. Both draining and wetting hydraulic functions were measured to assess the effect of root growth on soil water hysteresis Concurrent with the hydraulic property measurements, duplicate soil columns were destructively sample to characterize the root-growth distribution. Changes in the hydraulic conductivity function, pore-size distribution, and water retention as a result of plant growth will be discussed.
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