Hedging against erosion - planted stiff grasses prevent soil erosion

Agricultural Research, Dec, 1992 by Hank Becker

Stiff grasses could be a low-tech solution to a widespread problem. Just as grasses planted along beaches protect sand dunes from wind and water erosion, stiff grasses could help U.S. farmers solve a major problem-- protecting valuable topsoil.

In India in 1988, two World Bank agriculturalists extolled the virtues of using live hedges of vetiver grass (Vetiveria zizanioides) for controlling water erosion and argued their merits over U.S. bulldozer-built terraces. Doral Kemper, national program leader for soil management, was there with other ARS experts as an adviser on soil management technology for the U.S. Agency for International Development.

"It was a somewhat humbling experience," Kemper recalls. "As representatives of the country that has mounted the most extensive erosion control effort on planet Earth, we were less than wholly receptive to the message of the World Bank agriculturalists. They were saying that bulldozer-built terraces like those we use in the United States disturb topsoil and take water away too quickly--rather than letting it soak in. And that vetiver grass hedges do a better .job of controlling erosion and conserving water--at much less cost--than terraces formed by earthmoving equipment."

With the aid of literature and slides, these vetiver enthusiasts provided strong evidence that the grass was fulfilling these claims in India, the West Indies, and Fiji.

"Slim, green rows of vetiver grass planted by farmers across hillsides 10 to 30 years ago grew into thick, sturdy grass hedges 9 teet tall and 6 to 7 feet wide. They slowed runoff significantly and deposited sediment," Kemper says. "Over the years, these deposits have formed wide, productive bench terraces uphill from the hedges."

Stateside, Kemper, working with cooperators at USDA's Soil Conservation Service (SCS), found out more about the grass. Until the mid-1940's, vetiver was grown in the southern states and was prized for its valuable roots containing an aromatic oil used for making long-lasting perfumes. After chemists found out how to synthe-size perfume, commercial production of the grass practically ceased.

Seeds of vetiver collected in that era were found by ARS agronomist Gilbert Lovell at the Regional Plant Introduction Station, Griffin, Georgia. Some of those seeds were still viable after almost 40 years in storage.

Next, Kemper and SCS national plant materials specialist Curtis Sharp called together interested ARS, SCS, and university personnel to coordinate research and development activities on grass hedges for controlling erosion.

The group soon learned that using grass hedges is not a new idea here either. About 40 years ago, SCS proposed using hedges for developing natural terraces on steep lands.

"We're not sure why the idea didn't catch on," Kemper says. "We suspect that farmers were in a hurry to get their terraces built and earthmoving equipment became readily available to do the job. Since the government subsidized the construction of terraces, farmers adopted the quick alternative."

The group began testing different types of vetiver grass at a dozen U.S. locations to find out whether it would live up to World Bank expectations.

"All the vetiver types grew well over the summer. But winter freezes killed most stands," Kemper says, "except for several hedges planted by SCS plant materials specialist Mike Materne across shallow gullies at Fort Polk, Louisiana, where U.S. Amy tank maneuvers had denuded extensive areas. There, the 100-foot-long vetiver hedges not only flourished, but caught sediment 18 inches deep on the upslope side in just a year."

Evaluating Other Grasses

Materne' s findings were so encouraging that the group began a search for other grasses with stiff stems that wouldn't bend over when water ponds up against them and that are adapted to the climates of various U.S. regions.

Kemper found one candidate grass growing outside his office at the Beltsville Agricultural Research Center, Maryland. He had been watching an ornamental silvergrass, (Miscanthus sinensis Andersson), grow thick, closely packed stems and survive several cold winters.

Also thriving in nearby plantings were several closely related silver-grasses planted in 1980 by ARS' Jack Murray and Kevin Morris, of the National Tuff Grass Association. They provided vegetative silvergrass to Materne, who multiplied it in Louisiana plots during the winter months and made it available to all who needed it the following spring.

In 1991, silvergrass hedges were tested on erosion plots near Oxford, Mississippi. About a month before cotton planting, clumps of 1-foot-tall grass from Materne were planted about 7 inches apart and uphill from the lower ends of 72-foot-long plots with 5-percent slopes.

"Just one row of the grass held back nearly half of the soil lost or eroded from plots without hedges," says Keith McGregor, ARS agricultural engineer at the USDA National Sedimentation Laboratory in Oxford.

From May through September, about 14 tons an acre of soil were lost on grass-hedged plots that were conventionally tilled compared to 24 lost on plots without hedges. On untilled plots, these losses were 0.7 tons with hedges versus 1.3 without.