Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/12/2003
Publication Date: 3/1/2004
Citation: Hubbard, R.K., Sheridan, J.M., Lowrance, R.R., Bosch, D.D., Vellidis, G. 2004. Fate of nitrogen in the southeastern coastal plain. Journal of Soil and Water Conservation. 59(2):72-96. Interpretive Summary: The southeastern Coastal Plain is a broad region which includes varied geohydrolgic conditions. The commonality of the region includes generally warm temperatures, particularly during the summer months, and high rainfall. The weathered soils of the region require relatively high input of N for adequate crop production. The high input of N for crop production, supplementary irrigation, and the expanding number of CAFOs in the southeastern Coastal Plain increase the probability for N movement to surface or groundwaters. Solute movement studies by the Southeast Watershed Research Laboratory (SEWRL) over a 20 year period plus recently completed research showed that NO3-N movement rates in Coastal Plain soils and through the vadose zone ranged from a maximum of 9 m within one year after N fertilizer application to a deep sand, to a minimum of no observed changes in NO3-N concentrations at 6 m depth in soils with very impermeable subsoil horizons, regardless of N application rate at the soil surface. Nitrates were found in the groundwater at 6 m depth, but since levels did no change since prior to the start of the study, rate of movement apparently is in excess of 9 years. A series of studies on N entering the riparian buffer zones by surface runoff or shallow subsurface flow showed that these zones function as filters to assimilate N such that Coastal Plain streams have low N contents. The implications of these findings for soil and water quality are that N application rates and management techniques are critical on southeastern Coastal Plain soils, particularly the deep sands, and that in order to protect surface water bodies from NO3-N contamination, riparian buffer zones must be retained or reestablished. These findings show that crop production N application rates and timing need to match crops, soils, and environmental needs, as opposed to recommendations based on "average" crop needs independent of soil type.
Technical Abstract: Nitrogen (N) contamination of surface or groundwater is of health concern for both humans and animals. Excess N in surface water bodies may contribute to eutrophication. Elevated nitrate (NO3-N) concentrations in drinking water have caused infant death from the disease methemoglobinemia. Formation of potentially carcinogenic nitrosamines in the soil from nitrite (NO2-N) and secondary amines is also a health concern. Both NO3-N and NO2-N (generally referred to collectively as NO3-N) to groundwater is of particular concern in the southeastern Coastal Plain because of the unique climatic and geohydrologic regimes of the region. The southeastern Coastal Plain climatically is characterized by warm temperatures and relatively high rainfall. Because of the length of the growing season, multicriopping, which requires multiple applications of N, is commonly practiced. Annual rainfall distribution often also requires use of supplemental irrigation. The combination of relatively high N inputs, high rainfall, and use of irrigation of crop production couples with areas of permeable soils and geologic materials means that portions of the Coastal Plain may have high potential for N contamination of surface and ground waters. Research at the Southeast Watershed Research Laboratory (SEWRL), USDA-ARS, in cooperation with the University of Georgia over the past 20 years has focused on determining factors affecting N transport and transport rates over a range of Coastal Plain soils and management scenarios. This paper examines the finding from these extensive studies, reports new findings from a long term study, and couples all information to examine the long-term implications for N contamination of soil and water in the southeastern Coastal Plain.