Buffering pesticides

MISSISSIPPI STATE, Miss. — Environmentalists and citizens concerned about agricultural chemicals moving into the environment from farms may take heart from a project investigating the fate of pesticides.

David Shaw, a scientist with the Mississippi Agricultural and Forestry Experiment Station, has found that herbicides and other pesticides used by the agricultural industry are present in ground water at amounts below health advisory levels, even at times of peak pesticide usage. In the few instances that they are present above allowable levels, naturally occurring microbial, chemical and photochemical processes appear to aid in their degradation.

Still, Shaw wanted to find ways to further reduce the impact of lingering pesticides on the environment.

"We certainly want to do everything possible to minimize the load of pesticides in the environment because of the problems they can cause," Shaw said. "One question I asked was, ‘are there easy things, which are both farmer-friendly and environmentally-friendly, that can be done to reduce pesticide amounts?’"

Shaw looked at grass filter strips — a type of conservation buffer — as a possible remedy for pesticide runoff. Conservation buffers are small, vegetated areas or strips of land that slow water runoff. They can be planted at intervals within fields or at the edges of fields. Some examples of buffers include contour grass strips, filter strips, riparian buffers, wetlands and grassed waterways. Shaw said effective placement of buffers in and around fields can reduce soil erosion, as well as nutrient and pesticide runoff.

As part of his studies, Shaw and then-graduate student Al Rankins evaluated five species of grass — big bluestem, eastern gamagrass, giant reed, switchgrass and tall fescue — for their ability to filter out different herbicide treatments.

"We found that all the grass species we tested were able to reduce herbicide load in runoff by 50 to 80 percent," Shaw said.

Because these grasses have a broad range of physical characteristics and soil adaptability, several options are available to producers, he added.

"Conservation programs can be tailored to best meet the individual farm or farmer’s needs," Shaw explained.

Shaw and graduate student Brooks Blanche also tested the filtering effectiveness of grass buffers used as part of a comprehensive conservation system. Conservation tillage practices, such as no-till, have been adopted by many producers as a way to reduce soil erosion. But, Shaw said, results from earlier studies evaluating the impact of no-till systems on water quality have been mixed.

"There is an automatic assumption that if you go no-till, it must be beneficial for the environment," Shaw noted. "While this is certainly true in the case of the movement of soil sediment into water, it’s not as clear from a pesticide standpoint."

In his study, Shaw found that herbicide loss was two to five times higher in no-till and no-till/double-crop systems compared with conventional tillage. With a tall fescue buffer, herbicide runoff was reduced up to three times for no-till and no-till/double-crop systems. Shaw also saw reductions in herbicide loss when a tall fescue buffer was incorporated into conventional tillage systems.

"Just having a grass filter strip, even a small strip, has a significant effect on reducing herbicide runoff," Shaw said.

In other work, Shaw and then-graduate student Mark Shankle determined how buffer strips control herbicide runoff. To do this, they evaluated the soil properties of field areas planted with new and established buffer strips, and they compared them to areas that had not been planted with a buffer strip.

"Our results show that the organic matter content of soil increases by more than twofold when a buffer strip is planted," Shaw said. "This increases the soil’s adsorptive rate, stimulates microbial populations resident in the soil and greatly increases the breakdown of herbicides in runoff.

"One of the most striking things we observed is that in an established buffer strip, herbicide half-life was only 12 days, compared with more than 100 days when no buffer strip was present."

However, while buffer strips are relatively easy to establish and maintain, Shaw said producers should be mindful of them and use good management practices to insure their proper function.

"We’ve found that the grasses are sensitive to accidental oversprays or drift from many of the postemergence herbicides used in cotton and soybeans," Shaw said.

"Buffer strips are no panacea, but they are an effective tool for farmers in their efforts to maximize profitability, while at the same time preserving and enhancing our environment," he said.

For more information, contact Dr. David Shaw, 662–325–9575.

Charmain Tan Courcelle writes for MSU Ag Communications.

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