Impact of Agricultural Management Practices on Sediment and Nutrient Losses to Runoff

Z. Kabir, Aaron Ristow and W. Horwath

The experiment was conducted in the research plots and growers' fields in different agricultural management practices. Farming practices that preserve or enhance soil cover entering the rainy season appear to be effective at reducing cumulative runoff and, hence, nonpoint source pollutions (NPSP) load. In general, research plots and grower fields demonstrate challenges to agricultural runoff monitoring. Adherence to strict conservation tillage (CT) practices can immediately reduce fuel costs, but the potential benefits to water quality may take years to realize. In the short term, growers may have other water conservation options, including reconfiguring fields to reduce runoff velocity and thus erosion. Our research has shown that that winter cover crops (WCC) and CT can behave differently in California compared to other areas. On a farm scale, WCC significantly reduces winter runoff but also may affect subsoil water recharge and soil moisture content at the time of planting. The potential for winter WCC to alter the water budget of subsequent crops under furrow irrigation systems poses important questions, considering future water supply concerns. Additional research is needed to develop conceptual models that correlate water inputs and load reductions with alternative agricultural management practices in California. Such information would be beneficial to water quality stakeholders hoping to address future quality and supply issues.