INFILTRATION AND SOIL WATER STORAGE UNDER WINTER COVER CROPPING IN CALIFORNIAS SACRAMENTO VALLEY

Abstract

Winter cover cropping on agricultural fields may improve rainfall infiltration and enhance soil water storage inareas such as Californias Sacramento Valley, where the majority of precipitation occurs in the winter over a relatively shortperiod of time in a series of heavy rainfall events. Enhanced soil water storage within the root zone on covercropped fieldsmay 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 forsubsequent crops and to evaluate the effects of soil physical conditions on the water balance for three 4year rotation farmingsystems 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 maintainedfallow during the winter. Runoff and soil water content measurements were significantly affected by farming systems.<br><br>Cumulative event runoff from 10.67 m 2 infiltration test areas was consistently higher on the fallow treatment than on thecovercropped treatments. Winter 19992000 field water content measurements from 01.05 m depth were significantlyhigher in the covercropped systems than in the fallow treatment after field capacity had been reached. A hydrologic modelwas developed using the measured data and lysimeter data for evaporation and evapotranspiration to track daily water budgetcomponents (i.e., runoff, infiltration, evaporation, evapotranspiration, and soil water storage) and to assess changes insurface hydraulic conductivity. Model simulations showed that optimized hydraulic conductivity decreased for all treatmentswith successive runoff, but was less pronounced in covercropped plots. The study indicated that cover cropping can improvesoil water storage for subsequent crops if the cover crop is destroyed before the additional soil water is lost asevapotranspiration.