Grass filter strips placed in riparian zones not only curb soil erosion, but can help block and degrade a widely used herbicide, according to Agricultural Research Service reports.

Atrazine has been used extensively to suppress weeds for decades. But because it's applied directly to soil, it's especially prone to losses in surface runoff.

The contamination of surface water by atrazine and its less-toxic breakdown components has raised ecological concerns.

Riparian zones are transitional areas between upland areas, such as crop fields, and water bodies. The grasses and other vegetation in these zones help reduce pollution in streams and lakes.

Bob Lerch, a soil scientist in the ARS Cropping Systems and Water Quality Research Unit in Columbia, Mo., is working with colleagues in the unit and University of Missouri research assistant professor for forestry Chung-Ho Lin. They are studying the effect of different grass species on herbicide transport and degradation in field and growth chamber studies.

In the growth chamber, the grasses studied were orchardgrass, smooth bromegrass, tall fescue, Illinois bundle flower, ryegrass, switchgrass, and eastern gammagrass. Plants were allowed to grow for three months, to maturity. The rhizosphere soil—the soil zone that surrounds and is influenced by the roots of plants—was then separated from the plants and roots.

Atrazine was then added to the rhizosphere soils and incubated in the dark for 100 days at 77° F. The researchers then measured atrazine degradation and mineralization—the conversion of atrazine to carbon dioxide.

Among the plant species, eastern gammagrass showed the highest capacity for promoting atrazine degradation. More than 90 percent of applied atrazine was degraded to less-toxic forms, compared to 24 percent in the control. Rhizosphere soil of orchardgrass, smooth bromegrass, and switchgrass also enhanced atrazine degradation.

The studies have shown that grass buffers reduced the transport of herbicides to shallow groundwater and in runoff. These buffers can reduce herbicide transport through trapping of sediment and by increased infiltration of water into the soil.