One way farmers can preserve soil and protect water quality is by planting grass hedges to trap sediment that would otherwise be washed away by field runoff.
Agricultural Research Service (ARS) scientists at the agency's National Sedimentation Laboratory in Oxford, Miss., have calculated how much soil erosion these hedges prevent and verified predictions of the Revised Universal Soil Loss Equation version 2 (RUSLE2).
Agronomist Seth Dabney, hydrologist Glenn Wilson and agricultural engineer Robert Cullum collaborated with retired agricultural engineer Keith McGregor in a series of studies over 13 years to assess the effectiveness of grass hedges for erosion control in wide or ultra-narrow-row conventional tillage or no-till cotton systems.
The researchers established single-row continuous swaths of miscanthus, a tall perennial grass, across the lower ends of 72-foot-long plots with a 5% slope. Then they tracked how much sediment was trapped by the vegetation from both the wide and ultra-narrow-row conventional tillage and no-till fields. The hedges eventually became a yard wide and were clipped two to three times every year after the grass was 5 to 6.5 feet tall.
The scientists found that the ability of the hedges to trap sediment increased as the hedges matured. The hedges were more effective at intercepting sediments that washed out of conventionally tilled fields, possibly because the eroded materials from no-till fields were composed of smaller particles.
The hedges captured approximately 90% of eroded sediment from ultra-narrow-row conventionally tilled fields, and only about 50% of sediment from no-till fields. Nevertheless, the actual soil loss from the no-till plots — either with or without grass hedges — was much less than the conventionally tilled plots with or without grass hedges, because no-till production helps mitigate erosion.
The team also found that hedge effectiveness was enhanced when clippings were allowed to accumulate uphill of the hedges. But even if all the clippings from grass hedges over 1.5 feet tall are removed for livestock feed or bioenergy production, the hedges can still help protect against field erosion.
Hedges could be especially valuable if highly erodible lands in the U.S. Department of Agriculture (USDA) Conservation Reserve Program are brought back into production.