Author
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Hubbard, Robert |
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Submitted to: Meeting Proceedings
Publication Type: Proceedings Publication Acceptance Date: 3/24/2010 Publication Date: 5/24/2010 Citation: Hubbard, R.K. 2010. Impacts of Agriculture on Nitrates in Soil and Groundwater in the Southeastern Coastal Plain. Meeting Proceedings. Interpretive Summary: Pollution from agrichemicals and animal wastes may have negative impacts on human and animal health. The SE Coastal Plain is a broad region, which includes varied geohydrologic conditions. The commonality of the region includes generally warm temperatures, particularly during the summer months, and high rainfall. The weathered soils of the region have low indigenous organic N contents and require relatively high input of inorganic or manure N for adequate crop production. The high input of N for crop production, supplementary irrigation, and the expanding number of confined animal feeding operations (CAFOs) in the SE Coastal Plain increase the probability for N movement to surface or ground waters. Solute movement studies by the SEWRL over a 25 year period showed that NO3-N movement rates in SE 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 over 9 years at 6 m depth in soils with very impermeable subsoil horizons, regardless of N application rate at the soil surface. A series of studies on NO3-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 SE 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. The findings showed 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 and groundwater is a 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. Nitrates have also been shown to negatively affect the metabolism of domestic animals. Movement of NO3-N to groundwater is of particular concern in the southeastern Coastal Plain because of the unique climatic, soil morphology, and geohydrologic regimes of the region. Climatically, the southeastern Coastal Plain is characterized by warm temperatures and relatively high rainfall. Because of the extended growing season, multicropping, 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 for crop production coupled with areas of permeable sandy-textured soils and geologic materials means that large portions of the coastal plain may have high potential for NO3-N contamination of surface and ground waters. Research over the past 25 years at the Southeast Watershed Research Laboratory USDA-ARS has focused on determining factors affecting NO3-N transport amounts and rates over a range of coastal plain soils and management scenarios. This paper presents the findings from these extensive studies, reports findings on methods for protecting or renovating water quality including use of vegetated buffers and/or floating vegetated mats, and synthesizes all information to examine the long-term implications of NO3-N contamination of soil and water from agriculture in the southeastern Coastal Plain. |
