Agricultural activities are potential non-point sources of pollution of California's surface water. New regulations are now holding California growers accountable for detected pollutants draining off of their land. Conservation tillage (CT) and winter cover cropping (CC) are two practices for reducing runoff and minimizing nutrient and sediment losses. Automated water samplers on long-term research plots and farmer fields provide year-round monitoring of surface runoff. Runoff volume and quality of water constituents such as suspended sediment, P, N, and dissolved organic C are being determined. The objective of this study is to quantify discharge and to measure concentrations and load of runoff constituents of concern in a semi-arid climate from fields farmed under Fallow, CT, and CC systems. Results from the grower's fields during the 2003-2004 rain season show a stark contrast in runoff quantity between a field planted in a winter legume/oats CC and a field with no plant cover (NCC). Notably, the quantity of runoff discharged from the winter CC field was less than one-tenth the runoff of winter NCC field. In addition, the NCC treatment demonstrated significantly higher concentrations of sediment, P, NH4+, and dissolved organic N over the rain season when compared to the CC treatment. For summer 2004 irrigation season, cumulative discharge from winter CC field was estimated to be 25% of NCC field discharge. However, CT management of plots and fields produced greater loads of water constituents of concern compared to non-CT management. CT plots were within first two years of management and so it appears that CT may take years to realize positive benefits for water quality. Relationships of surface runoff from rainfall/irrigation and management practices will continue to be used to develop monitoring tools for different land uses and management practices to minimize the export of water constituents of concern.