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Grass hedges curb runoff

SWITCHGRASS, A sturdy rangeland grass being considered for livestock feed and for fuel alcohol production, may also prove useful in stiff-grass hedge plantings that help curb soil erosion.

Agricultural Research Service scientists are evaluating the effectiveness of switchgrass, Panicum virgatum, and eastern gamagrass, Tripsacum dactyloides, for controlling water-driven soil erosion.

Hydraulic engineer Darrel M. Temple at ARS' Hydraulic Engineering Research Laboratory in Stillwater, Okla., working with agronomist Seth M. Dabney at ARS' National Sedimentation Laboratory in Oxford, Miss., have determined the depth of water that different widths of hedges can retain before being bent over and overtopped.

The scientists tested narrow, parallel strips of switchgrass and gamagrass in an outdoor laboratory. In field applications, these hedges are planted close to the contour of slopes and form a porous barrier to flowing water, causing it to pond above them, and diffusing the flow over a large area as the water passes through them.

Temple and Dabney tested the hedges by discharging more and more water through them until the grasses bent and broke under the flow. Switchgrass proved to be better able to withstand the pressure than gamagrass, standing erect and holding back sediment and water. The one- and two-row hedges were found to be nearly as effective as the wider three- and four-row hedges tested.

For the next two years, the scientists will focus on the ability of switchgrass hedges to protect the soil from concentrated waterflow on very steep slopes that are already eroded.

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