Restored riparian wetland buffers retained or removed at least 60 percent of the nitrogen and 65 percent of the phosphorus that entered from an adjacent site where manure was applied, according to results of a nine-year study by Agricultural Research Service scientists in Tifton, Ga., and cooperators at the University of Georgia.
This is the first time that a study of a restored riparian buffer has shown that the retention of phosphorus was as high or higher than nitrogen retention. Riparian buffer zones are areas of vegetation that act like sponges, soaking up water and nutrients from the soil. Buffer zones also help reduce soil erosion along downward slopes due to rain or irrigation, both of which can cause surface runoff.
Ecologist Richard Lowrance of the ARS Southeast Watershed Research Unit, and Engineer George Vellidis of the University of Georgia, found that a particular type of buffer — called a restored Zone 3 Conservation Buffer — is especially effective in removing excess nutrients from water that runs off of agricultural fields where manure has been applied as a fertilizer. A Zone 3 buffer is a grassy edge that sits next to the field.
During the study, the amount of water and concentrations of nutrients (nitrogen and phosphorus) in water entering and leaving the riparian wetland were monitored. The stream flow concentrations of nitrogen and phosphorus leaving the conservation wetland buffer were one-half (for nitrogen) and one-quarter (for phosphorus) of the incoming concentrations in surface runoff from adjacent fields.
Other Tifton scientists are conducting various conservation buffer research studies that examine several different scenarios farmers encounter. Ultimately, this research should help growers develop a way to lower nutrients that make it to streams and waterways.
ARS is the U.S. Department of Agriculture's chief scientific research agency.