Additional Research Shows Promise for Buffer Zones

Narrow strips of vegetation on the edges of farm fields can do a lot to help keep sediments and pesticides from draining into adjacent streams, a recent comparative study by University of Nebraska School of Natural Resource Sciences researchers indicates.

"Most early research on vegetative buffer strips was done in the east and southeast (United States) and what they found there doesn't necessarily hold with what we're seeing here," said NU aquatic ecologist Kyle Hoagland.

Buffer strips can be planted to a variety of vegetative cover types and widths. They typically are placed between farm fields and the streams they drain to. Most guidelines have called for forest buffers to be planted 95 feet wide or more to control runoff. Recent NU research indicates that much narrower widths may be efficient in reducing non-point source runoff pollution in Nebraska buffers.

The NU study by soil scientist Mike Dosskey, graduate student Tim Schmitt, and Hoagland compared strips just 25 and 50 feet wide. Four different vegetative cover types were compared for each of the two widths: 25-year-old native grasses; two-year-old grass; two-year-old grass with trees and shrubs; and cultivated grain sorghum. Studies and demonstrations were conducted at NUs Agricultural Research and Development Center.

Plots were tested under conditions that simulated runoff that might occur from a typical spring thunderstorm, passing known amounts of water and contaminants through the strips. The runoff water was collected after having flowed through the strips and later analyzed for sediments and contaminants.

Grass strips, with and without trees and shrubs, were very effective at reducing amounts of sediment in runoff (76 to 93 percent effective), but less effective at reducing dissolved contaminants such as atrazine, nitrate and dissolved phosphorous. Doubling the width of the strips from 25 to 50 feet didn't substantially improve sediment settling.

Compared to the grain sorghum strips, "The newly planted (grass) buffer strips reduced sediment and attached contaminants in runoff, but had no clear effect on runoff volume or concentration of dissolved contaminants," Hoagland said. Older buffers were more effective at reducing dissolved contaminants.

"The level of water quality improvement that we can expect from filter strips is highly dependent on the cropping practices that they replace near the stream," Hoagland said.

The Nebraska Department of Environmental Quality and U.S. Environmental Protection Agency, Region VII helped sponsor the research.