Aug. 15, 2003

TEMPLE - Using grass filter strips can significantly reduce the amount of herbicide runoff associated with crops near adjacent lakes, rivers or streams.

This has been shown as part of an ongoing project conducted at the Texas A&M Blackland Research and Extension Center at Temple. "We've seen as much as a 50 percent reduction in atrazine and metolachlor,"said Monty Dozier, Texas Cooperative Extension water resources specialist.

Atrazine is a crop herbicide used to control broadleaf weeds, while metolachlor controls grasses. The research, conducted jointly by Extension and the Texas Agricultural Experiment Station, examines ways to reduce the amount of runoff associated with the two herbicides in an attempt to reduce the threat to bodies of water, such as streams and watersheds – some of which are sources of public drinking water.

In field testing conducted at the Blackland Research Center, 30-foot-wide bermudagrass filter strips were planted next to 1.5 acre corn experimental plots. A 180-foot concrete wing arm was used to collect runoff from each corn plot. This runoff flowed into a flume, allowing researchers to measure the volume and collect runoff samples generated by natural rainfall.

A stage recording device, which was housed inside a metal box next to the flume, was used to help measure water depth.

"It measures how much water is coming in and at what time," said June Wolf, an Experiment Station water biologist. "It also triggers a sampler. When the water reaches at a desired level, it will turn the water sampler on and collect the samples whenever we want it to."

Dr. Scott Senseman, an associate professor of weed science with the Texas Agricultural Experiment Station and supervisor of the water testing lab at Texas A&M University, analyzed the water samples.

"What we found right after the application and also when it rained hard, we saw a reduction in concentration," Senseman said. "That ranged up to 100 parts per billion."

Dr. Dennis Hoffman, an Experiment Station research scientist based in Temple, said the concrete wing arms were first constructed at the Blackland Research Center in 1938 as part of a Civilian Conservation Commission project. In 1992, Hoffman began collecting atrazine data.

"When I started out here they had not been used in about 20 years," Hoffman said. "From an atrazine standpoint, conducting these tests was like going on virgin land because there had never been any herbicide used here before."

While the tests revealed up to 50 percent atrazine reduction, the reason why is still a bit of a mystery, Hoffman said.

"We're not sure where it's going, probably absorption in that organic layer at the base of the plants," Hoffman said. "Sometimes the filter strip will impact how much water comes off of them, but overall it's safe to say this reduces atrazine in runoff by as much as 50 percent."

Dozier said experiments conducted between 1995 and 2002 revealed at least 50 percent atrazine reduction with the exception of 1998, 1999 and 2001 due to drought.

The filter strip practice has been put to use by commercial farmers on about 276 acres in Ellis and Navarro counties, Dozier said.

"It's mainly been targeted for those farmers in the Central Texas Blacklands region," he said.