These two states and several others are in the process of making regulations for application of animal waste based upon phosphorus as the limiting nutrient. Recent research by Ham, a graduate student in the Soil Science department at NCSU, has shown that some sandy soils that have received animal waste for many years have significant increases of phosphorus to a depth of 4-5 feet. We have no indication that this phosphorus is moving laterally to streams, but there are questions as to how much phosphorus can be added to soils before this kind of movement becomes significant. As of this date, North Carolina soil scientists have not determined a recommended level of soil phosphorus on which waste applications should be based. A prominent feature of most North Carolina landscapes is the forested area present as narrow bands on either side of small streams.
Riparian areas are extremely important for water quality protection in North Carolina.
Nitrogen from nonpoint sources most often enters streams through subsurface flow of nitrate from agricultural fields. When the subsurface flow passes below a wooded riparian area, greater than 90 percent of the nitrate is frequently removed from the water before it enters streams. In North Carolina, data show that drainage water from agricultural fields containing 10-20 milligrams per liter of nitrate nitrogen contains less than 1 milligram per liter when it enters the stream because of nitrate removal by riparian buffers. Denitrification converts the nitrate, which can contaminate surface and ground water, to a harmless dinitrogen gas that already makes up 80 percent of the air. Since we do not know how to grow crops with sufficiently high yields to feed our population without loss of nitrate to groundwater, it is important that we take measures to prevent this nitrate from reaching surface waters where it may cause eutrophication problems.