"We sampled the water right above the buffer coming right off the sprayed area, then about three feet into the buffer, then another 12 feet and then another 24 feet, so we can see how the reduction in the load and the concentration occurs as it goes through the buffer," Lerch said. "We did that because we were interested in not only how the different grass treatments work, but also how much buffer do you need."
Finding the correlation between the width of the buffer and how effective it is in reducing contaminants from herbicides has implications for design. That information can be given to the Natural Resources Conservation Service and other land management agencies.
"We found that grass buffers across the board were effective," Lerch said. "Every buffer was better than nothing."
The effectiveness drops off quickly in relation to the ratio of the drainage area to the buffer. A drainage-to-buffer ratio of 2-to-1 or less doesn't make much difference. The ratio is very sensitive in a certain range and then flattens out and has minimal effect.
"We can give them a good idea even though it was a plot-scale experiment of what you might expect in a real-field scale," Lerch said. "The relationship of how much contaminant is reduced versus the width of the buffer is really the basis for design criteria. For something like atrazine, if you have a 20-to-1 drainage to buffer ratio you will get 30 to 35% reduction. Is that good enough? Well, someone has to decide what is good enough, but we deliver the numbers."
NRCS has not yet adopted the findings into their technical field guides. Lerch says it takes time for the research to translate into what gets done in the field. The key is to educate people and make sure they understand the science so it can be effectively put into practice.
Source: University of Missouri Extension