Average median nitrate levels declined 97 percent, and average median ammonium levels dropped 76 percent. This indicated that using either riser pipes or weirs to temporarily trap field runoff could increase the capacity of drainage ditches to lessen runoff nutrient loads.

Tests in the West

Moore was asked by U.S. Environmental Protection Agency (EPA) environmental scientist Debra Denton to test the effectiveness of vegetated drainage ditches for mitigating pesticide runoff in California crop fields. Moore conducted a preliminary field trial in Yolo County, Calif., using a U-shaped vegetated ditch, a V-shaped vegetated ditch, and a V-shaped ditch with no vegetation. Each 545-foot ditch was amended for 8 hours with a mixture of diazinon, permethrin, and suspended sediment.

Afterwards, Moore’s team analyzed water, sediment, and plant samples for pesticide concentrations. They found that differences in half-distances — the distance that runoff travels in a ditch to reduce initial pesticide concentration by 50 percent — ranged from 69 feet in the V-shaped vegetated ditch to 485 feet in the V-shaped unvegetated ditch.

The researchers followed up with another study that evaluated the ability of existing drainage ditches alongside California tomato and alfalfa fields to mitigate runoff loads of the pesticides chlorpyrifos and permethrin. The scientists planted creeping wildrye and slender sedge — both native to California — in the V-shaped ditches about 5 months before the start of the irrigation season.

Water, sediment, and plant samples collected after the runoff events indicated that chlorpyrifos concentrations in alfalfa field runoff decreased 20 percent by the time it left the ditch. Thirty-two percent of the measured chlorpyrifos was associated with ditch plant material. Permethrin concentrations in runoff from tomato fields decreased 67 percent by the time it left the ditch, and suspended sediment concentrations dropped 35 percent.

With these findings in hand, Denton worked with USDA’s Natural Resources Conservation Service (NRCS) state office in California to include vegetated agricultural drainage in its Environmental Quality Incentives Program (EQIP). NRCS approved this designation in 2008, which meant that farmers who installed the ditches could be reimbursed for up to 50 percent of the cost.

“One of the best things about this project is that ARS and EPA were working side by side for the same goal — to help the farmers and improve water quality,” says Moore.

“Because of this work, other researchers in California are now studying ways to use vegetated drainage ditches to reduce pesticides, nutrients, and sediment loadings into waterways,” adds Denton. “But one of the things Moore emphasizes is that using vegetated ditches is just one practice in a suite of practices farmers can use to reduce agricultural pollutants in field runoff.”

Moore’s research contributed to the decision by NRCS managers in Mississippi to include vegetated agricultural drainage ditches in the state’s EQIP. Meanwhile, Moore is continuing his research.

“Our next step is figuring out the best ways to manage vegetation in the ditches,” Moore says. “But the farmers we talk with are cautiously optimistic about how the ditches can work for them. They do see that it could be a low-cost option for controlling nutrients and pesticides in runoff

This research is part of Water Availability and Watershed Management, an ARS national program (#211) described at www.nps.ars.usda.gov.

To reach the scientists mentioned in this story, contact Ann Perry, USDA-ARS Information Staff, 5601 Sunnyside Ave., Beltsville, Md. 20705-5129; (301) 504-1628.

"Drainage Ditch Research Reveals Opportunities for Cleaning Up Runoff" was published in the January 2013 issue of Agricultural Research magazine