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Winter cover cropping on agricultural fields may improve rainfall infiltration and enhance soil water storage in areas such as Californias Sacramento Valley, where the majority of precipitation occurs in the winter over a relatively short period of time in a series of heavy rainfall events. Enhanced soil water storage within the root zone on covercropped fields may benefit a grower by reducing the demand for surface water deliveries to meet the irrigation needs of subsequent crops. A study was conducted in the winters of 19981999 and 19992000 to determine a fields ability to conserve water for subsequent crops and to evaluate the effects of soil physical conditions on the water balance for three 4year rotation farming systems within the Sustainable Agriculture Farming Systems (SAFS) Project at the University of California, Davis. Rainfall, runoff, and soil water content data was collected on two treatments using a winter cover crop and one treatment maintained fallow during the winter. Runoff and soil water content measurements were significantly affected by farming systems.

Cumulative event runoff from 10.67 m 2 infiltration test areas was consistently higher on the fallow treatment than on the covercropped treatments. Winter 19992000 field water content measurements from 01.05 m depth were significantly higher in the covercropped systems than in the fallow treatment after field capacity had been reached. A hydrologic model was developed using the measured data and lysimeter data for evaporation and evapotranspiration to track daily water budget components (i.e., runoff, infiltration, evaporation, evapotranspiration, and soil water storage) and to assess changes in surface hydraulic conductivity. Model simulations showed that optimized hydraulic conductivity decreased for all treatments with successive runoff, but was less pronounced in covercropped plots. The study indicated that cover cropping can improve soil water storage for subsequent crops if the cover crop is destroyed before the additional soil water is lost as evapotranspiration.