Management practices to conserve water and reduce off-site movement of sediment and pesticides in drainage waters

The Issue

Drainage waters discharged from irrigated fields in California and other states are under ever-closer scrutiny. The quality of drainage waters discharged into waterways in California is regulated under California Water Code and Federal Clean Water Act. Growers that discharge drainage waters that could affect the quality of water bodies in the state are required to comply with water quality regulations. Compliance with water quality regulations could be achieved by filing a Report of Waste Discharge (RWD) that complies with state-prescribed Waste Discharge Requirements (WDRs). WDRs could be used as a permit, limiting the levels of pollutants that may be discharged in waterways to protect the beneficial uses of water bodies in the state. Complying with the Irrigated Lands Conditional Waiver Program or the Total Maximum Daily Load (TMDL) limits may provide alternates to WDRs for growers in the state.

Sediment, nutrients and pesticides in drainage waters have been identified as the leading cause of water quality impairments in rivers and other water bodies in California. For example, sedimentation/siltation TMDLs for agricultural drains and two major rivers in Imperial Valley have been implemented to address water quality problems in the Colorado River Basin of Southern California. Accurate and reliable estimates of the load of sediment, nutrients and pesticides in drainage water are needed to assess the quality of drainage water or to comply with WDRs.

What has ANR done?

To assist growers in complying with current water quality regulations with regard to sediment and the expected regulations with regard to pesticides, Imperial County farm advisor Khaled Bali, UC Riverside water quality specialist Jay Gan, and Imperial County UC Cooperative Extension director Eric Natwick evaluated the impact of several on-farm irrigation and insecticide management practices on water conservation and drainage water quality. The study was conducted on two alfalfa fields at the UC Desert Research and Extension Center near Holtville, Calif. The alfalfa fields were irrigated by border and furrow irrigation systems. The researchers applied a variety of insecticides on different test plots, then irrigated 1 to 11 days following the insecticide applications. Irrigation application efficiency and insecticide concentrations in runoff water were determined for the various treatments. The load and concentration of sediment in runoff waters were also measured for the two irrigation systems.

The Payoff

Delayed border irrigation increases water efficiency, reduces sediment and pesticide runoff

Water application efficiency was significantly higher on the border-irrigated field (79 percent) compared to the furrow-irrigated field (67 percent). Both sediment load and concentration in runoff water generated from the border-irrigated field were approximately one-sixth to one-third of that of the furrow-irrigated field. Pesticide concentrations in runoff water were reduced by 68 percent when irrigation events occurred four days after insecticide applications as compared to irrigation events one day after application. Water use efficiency and water quality indicators (sediment and pesticides) in border-irrigated alfalfa fields are significantly higher than those of furrow-irrigated fields.

Contact

Supporting Unit:

Imperial County , UC ANR Cooperative Extension and CNAS UC Riverside
 
Eric Natwick, (760) 352-9474, etnatwick@ucdavis.edu