Application of Beneficial Management Practices to Reduce Runoff from Irrigated Agriculture

completed

Contra Costa Resource Conservation District, in pursuing its mission to provide an organized means for land managers and local community members to play a prominent role in carrying out voluntary, cooperative conservation programs that promote the sustainable and productive use of natural resources in Contra Costa County, obtained funding from the State Water Resources Control Board’s Agricultural Water Quality Grant Program (AWQGP) to work with local growers in the county to address sediment in runoff from irrigated agricultural lands in eastern Contra Costa County by evaluating and installing “beneficial management practices” (BMPs) such as tailwater return systems, conversion to drip irrigation, vegetated buffer strips, and the use of polyacrylamide (PAM) to settle out sediment, and then to determine the type of BMPs that are most effective in improving the quality of runoff and discharges. Four agricultural operators in this targeted area volunteered to participate in the program. Drip irrigation systems (a pump, a series of filters, a mainline, pressure reducing valves, sub-mains, and drip tape) were developed on six project sites totaling 335 acres for the implementation of the most effective BMPs. In accordance with the AWQGP requirements, water quality monitoring was conducted on the fields. Irrigation tailwater samples from the fields utilizing the drip irrigation system, as well as from conventional furrow irrigation fields, were collected and analyzed for Total Suspended Solids, Specific Conductance, Total Organic Carbon, and for pH in order to quantify the effectiveness of the drip irrigation system as a BMP. The primary difference between the furrow irrigated fields and the drip irrigated fields was the reduced volume of tailwater discharged from the drip irrigated fields. Tailwater on the drip irrigated fields was typically non-flowing water, less than an inch deep, at the end of a furrow. The water quality measurements showed that the drip irrigated fields had much lower Total Suspended Solids values, which implies that there are lower concentrations of bacteria, nutrients, pesticides and metal which may attach to sediment particles and be carried into water bodies. Specific Conductance, Total Organic Carbon, and pH did not vary significantly from the furrow irrigated sites. Besides benefiting the water quality, the drip irrigation systems resulted in economic benefits as well. Converting irrigation systems to drip used less water, resulting in a decrease in water costs to the growers. It also resulted in a more uniform distribution of water and reduction of soil erosion, which allowed nutrients to be more effective. Crop yield increases ranged from 24% to 70% in four fields. The drip irrigated fields had fewer weeds, and required less maintenance. Implementing these practices resulted in economic and environmental benefits for growers in Contra Costa County. In fact, growers in the eastern Contra Costa County applied for Natural Resources Conservation Service Environmental Quality Incentive Program funding in 2007 to convert six fields, totaling 415 acres, to drip irrigation. The popularity of this BMP has thus achieved another desired outcome of the program: the sharing of project results with other growers and the increased use of effective management practices to improve offsite water quality.

Medium