Nitrogen contamination of groundwater in the nitrate (NO3-N) or nitrite (NO2-N) form is of health concern for both humans and animals. Elevated NO3-N concentrations in drinking water have caused infant death from the disease methemoglobinemia. Formation of potentially carcinogenic nitrosamines in the soil from NO2-N and secondary amines is also a health concern. Both NO3-N and NO2-N have been shown to negatively affect the metabolism of domestic animals. Movement of NO3-N and NO2-N (generally referred to collectively as NO3-N) to groundwater is of particular concern in the Southeast because of the unique climatic and geohydrologic regimes of the region. The Southeast climatically is characterized by warm temperatures and relatively high rainfall amounts. Because of the length of the 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 soils and geologic materials means that the southeastern US has high potential for groundwater NO3-N contamination. Current information on NO3-N leaching to groundwater in the Southeast is rather sparse. This chapter discusses processes and factors affecting NO3-N leaching, drawing information both from studies conducted in the Southeast and other regions of the USA or world, and also summarizes available information from the Southeast. Topics discussed include principles governing NO3-N transport to groundwater, physical factors affecting water and NO3-N transport in the southeastern USA, effects of management on NO3-N movement, current and potential impact of NO3-N on groundwater in the southeastern USA, role of models in assessing future impact and for guiding management decisions, and future research needs. Available research information on NO3-N movement to groundwater in the Southeast indicates that under presently used N application rates for agriculture, both root zone NO3-N concentrations and shallow groundwater NO3-N 304concentrations may exceed the 10 mg L−1 drinking water standard. Studies in both the Maryland and Georgia Coastal Plain have shown concentrations in excess of 10 mg in shallow groundwater. Much less is currently known about deeper groundwater in the southeastern US, but the research information available from the Midwest and other parts of the US and world clearly indicate the potential for NO3-N contamination of deeper groundwater. The main conclusion about the Southeast is that the weathered soils of the region require relatively high input of N for adequate crop production, and that this input coupled with high annual rainfall and irrigation results in significant probability for NO3-N movement to groundwater. Recommendations for minimizing NO3-N leaching to groundwater primarily are management and land use related. Management decisions include using minimum amounts of inorganic fertilizers, carefully controlling amounts of applied animal wastes, designing septic systems with adequate drain field areas, and minimizing percolation. Winter cover crops may be useful because they minimize nutrient availability for deeper movement during the seasonal wet periods of the winter-spring months, when most subsurface movement and percolation occurs. One major land use tool which may assist in limiting NO3-N leaching to groundwater is the use of riparian zones to remove NO3-N from water either by denitrification or by vegetative uptake. Future research needs for the Southeast include new information on the effects of currently used agricultural practices on NO3-N movement to groundwater, and field, laboratory; and modeling work to better understand factors and processes affecting NO3-N leaching for this region.

Conservation tillage (CsT) involves management that reduces soil erosion by maintaining crop residue cover on farm fields. Typically, both infiltration and soil organic matter increase over time with CsT practices. We compared the impact of a commonly used CsT practice, strip tillage (ST), to conventional tillage (CT) management on soil nitrogen (N) dynamics and leaching and examined associations to soil N availability and microbial biomass. A winter cover crop was used in both tillage treatments. The study was conducted over a five-year period during rotational cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.) production in the Atlantic Coastal Plain region in Georgia, United States. Fertilizer and poultry litter were applied ahead of the cotton crops. Sets of PVC cylinders were filled with soil from each of six plots, three in ST and three in CT, and maintained in situ in their respective plots for 16 intervals of about 90 days. After retrieval, the soil in each cylinder was analyzed for inorganic N (ammonium and nitrates [NH4+ and NO3−]), total N, total carbon (C), and microbial biomass. Leached NO3−-N was captured on anion exchange resin-filled bags attached to the bottom of each cylinder. After the five-year study period, the ST and CT soil C content increased by 22% and 23%, respectively. Total soil N content increased 27% with ST compared to 22% with CT. Temporal patterns in NO3−-N leaching were not different between CT and ST treatments, and a high amount of NO3−-N leaching was observed after the application of poultry litter. The cumulative amount of NO3−-N leached from soils throughout the five-year study was 141 and 122 kg N ha−1 (126 and 109 lb N ac−1) with CT and ST practices, respectively. Results suggest that leaching from the top 15 cm (6 in) of soil may be an important pathway of N loss from both CT and ST cropping systems in the region. Regardless of tillage, soil microbial biomass N was equal to or higher than the total inorganic N, but still represented a small percentage (up to 9%) of the total soil N. Overall, microbial biomass N was higher in ST compared to CT. Minimizing NO3−-N in the soil from reaching ground and surface waters while increasing crop productivity represents a major challenge. The use of ST in conjunction with winter cover crops may improve plant N availability by more than 27 kg ha−1 y−1 (24 lb ac−1 yr−1) in the sandy landscapes of the southeastern Coastal Plain region through microbial cycling of organic N while reducing subsurface NO3−-N losses.

Losses of soluble nutrients from cropland and their transport to surface and groundwater are a continuing water quality concern. In this study, we evaluated tillage impacts on dissolved losses of ammonium (NH4-N), nitrate nitrogen (NO3-N), chloride (Cl), and potassium (K) during rotational cotton and peanut production. Tillage treatments were strip tillage (ST), in which crops were planted into 15 cm strips tilled into cover crop residue mulch, and conventional tillage (CT), in which all crop residues were turned into the soil prior to planting. Winter cover crops were used in both tillage systems. Tillage and irrigation treatments were uniformly applied within two 0.6 ha fields located on a moderately sloping hillslope in the southern Atlantic Coastal Plain region of south-central Georgia. Tile drains were installed at the base of the slope of each field to capture and measure lateral subsurface flow. Each field was subdivided into three 0.2 ha plots, with the three plots making up a single tillage block. H-flumes were used for flow measurement and sample collection. During the five-year study, annual precipitation ranged from 910 to 1488 mm, with an annual average of 1201 mm. Annual surface runoff averaged 17% of annual rainfall from the CT field and 11% from the ST field. Because of relatively low variability in concentrations, surface runoff loads closely tracked surface runoff volumes. Annual surface runoff loadings of NH4-N, NO3-N, and Cl from the ST treatment were found to be significantly less than those from the CT treatment. The total five-year load of N (NH4-N and NO3-N) in surface runoff from CT was 8.3 kg ha(-1), while it was 5.6 kg ha(-1) from ST, equivalent to 1.5% of the total N applied to CT and 1.0% of that applied to ST. Annual subsurface flow averaged 12% of annual precipitation for CT and 21% for ST. Annual average subsurface flow loadings of NH4-N, NO3-N, and K from ST were significantly greater than from CT. The total five-year load of N (NH4-N and NO3-N) in subsurface flow was 45 kg ha(-1) from CT and 99 kg ha(-1) from ST, equivalent to 8.3% and 18.4% of the total N applied to CT and ST, respectively. Data showed that subsurface flow was the primary hydrologic pathway for dissolved N and Cl loss in both tillage systems. Overall, ST was found to be an effective method for reducing surface runoff and associated soluble losses, but increased infiltration with this practice significantly increased subsurface losses. This introduces a challenge to nitrogen management in reduced tillage systems such as ST in the region.

Although conservation tillage is widely believed to be an agricultural management practice effective for increasing soil carbon (C) accretion and associated soil quality, there is limited research to determine whether conservation tillage increases net C accretion versus simply altering the distribution of C content by soil depth. We implemented conservation farming practices (winter cover cropping plus strip tillage) for a nonirrigated corn (Zea mays L.) production system in the southeastern coastal plain of Georgia, United States, that had been previously managed under a conventional plow and harrow tillage regime. Total soil C and nitrogen (N) were measured on samples collected from 0 to 65 cm (0 to 25.6 in) at 57 sites before and after five years under conservation farming practices. Crop yield, winter and summer aboveground crop biomass production, and biomass C and N content were also measured annually at each site. Soil C increased an average of 20 Mg ha(-1) (8.9 tn ac(-1); 6 to 62 Mg C ha(-1) [2.6 to 27.6 tn C ac(-1)], depending upon slope position) and was associated with a N increase of 2 Mg ha(-1) (0.89 tn ac(-1)). Although 72% to 80% of the C accretion was in the top 35 cm (13.8 in), 3 to 6 Mg C ha(-1) (1.3 to 2.6 tn C ac(-1)) was accreted from 35 to 65 cm (13.8 to 25.6 in). The soil C accreted during the study amounted to 36% of the net biomass C produced. Corn yield increased 2,200 kg ha(-1) (1,964 lb ac(-1)) depending upon slope position (1,200 to 2,500 kg ha(-1) [1,071 to 2,232 lb ac(-1)]) during the same time. Analysis indicated that soil C content from 15 to 35 cm (5.9 to 13.8 in) was the soil parameter primarily associated with corn yield. Season rainfall from planting to corn silking stage for both corn production years was the lowest in the past 45 years (20 to 25 cm [7.8 to 9.8 in] below the net crop demand) suggesting that soil C-mediated increase in plant-available soil water was a mechanism contributing to improved corn yield. Calculated estimates (from soil clay, sand, and C content) of increased soil water holding capacity suggest that C accretion in the top 35 cm (13.8 in) of soil potentially increased water storage enough to supply up to four days' worth of additional crop water demand. These results indicated that conservation farming practices can increase soil C and N accretion in degraded sandy soils of the humid southeastern United States coastal plain, and that increased soil C may potentially mitigate the deleterious effects of short-term rainfall deficits in nonirrigated production systems.

Methods are needed for utilizing nutrients contained within animal wastewater lagoons. One potential method for capturing nutrients in a useful form is to grow vegetation on the lagoon. A study was conducted from 2005 to 2008 to determine the feasibility of growing vegetation on floating platforms on a single-stage swine wastewater lagoon. Five species were selected from earlier studies as having potential for growth on a commercial swine farm wastewater lagoon: common bermuda grass (Cynodon dactylon (L.) Pers.), Tifton 85 bermuda grass (Cynodon dactylon (L.) Pers.), St. Augustine grass (Stenotaphrum secundatum (Walter Kuntze)), fall panicum (Panicum dichotomiflorum (L.) Michx.), and giant reed (Arundo donax L.). The plants were periodically harvested as needed, and the biomass was weighed and analyzed for N, P, K, Ca, Mg, S, Al, B, Cd, Cr, Cu, Fe, Mn, Mo, Na, Ni, Pb, and Zn. Giant reed and St. Augustine grass were found to be unsuitable for long-term growth on the wastewater lagoon. The greatest biomass production (sum of six cuttings) was 3.6 kg m(-2) dry matter from Tifton 85 bermuda grass, followed by common bermuda grass (3.2 kg m(-2) dry matter) and fall panicum (3.1 kg m(-2) dry matter). All of the plant species accumulated greater than 1000 ppm Na. Nutrient (N, P, and K) uptake and removal from the wastewater with biomass harvesting was primarily a function of biomass produced. The greatest annual uptake and removal of N and P from the wastewater was by Tifton 85 bermuda grass in 2006, where three cuttings of the floating vegetation removed totals of 69 and 25 g m-2 N and P, respectively. Annual uptake and removal of K was greatest by fall panicum, where uptake and removal by three cuttings in 2007 totaled 78 g m-2. In 2008, weeds that had populated the mats were harvested for biomass and elemental uptake. Uptake and total removal of nutrients in two cuttings of the weeds in 2008 was lower than what was observed with the planted species. Total uptake and removal of N, P, and K by the weeds in 2008 was approximately 30, 10, and 30 g m(-2). The study showed that plant species exist that can grow and thrive on single-stage anaerobic wastewater lagoons on floating platforms for at least two years while taking up N, P, and K from the wastewater. Harvesting of biomass (which could potentially be used as a soil amendment or as cellulosic feedstock for bioenergy) from floating mats hence could be a mechanism for animal producers to both remove and productively use nutrients contained in the wastewater.

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2011Incorporating well, rock physics, and geological information into anisotropy estimates enables a “true earth model”Authors: Huyen BuiRobert HubbardDave WattsChih‐Wen KueDavid NgMart SmithHuyen BuiWesternGecoSearch for more papers by this author, Robert HubbardWesternGecoSearch for more papers by this author, Dave WattsWesternGecoSearch for more papers by this author, Chih‐Wen KueWesternGecoSearch for more papers by this author, David NgWesternGecoSearch for more papers by this author, and Mart SmithWesternGecoSearch for more papers by this authorhttps://doi.org/10.1190/1.3628026 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract Current industry practice considers the influence of anisotropy on imaging. The most important thing is how to indicate and estimate anisotropy for anisotropic velocity model building. In a previous work, we presented the valuable indicator of anisotropy based on well‐seismic misties (Bui et al., 2010). In this paper, we introduce the concepts and a method to estimate anisotropy by incorporating well, rock physics, and geological information. It is very well‐known that anisotropic parameters are poorly resolved by seismic data alone. Incorporation of the well and geological information, such as check shot, calibrated sonic, and geological markers will help to improve seismic resolution. Our prime goal is to understand the effect of geological constraints on anisotropy as well as anisotropic seismic velocity in each study area. To do this, we must determine geological constraints by mapping geobodies/seismic horizons from seismic interpretation with the set of well logs. The goal of modern imaging is to tie seismic events with well markers to accurately position hydrocarbon reservoirs based on the indicator from seismic‐to‐well tie. We use a 1D ray‐tracing model for building an anisotropic model from seismic data with well control. The concepts are to match the seismic events with the well markers as well as flatten common‐image‐point (CIP) gathers. We also incorporate the rock physics information with the 1) seismic velocity correction at well location, and 2) constrain the anisotropy estimation for each seismic sequence. Then, the 1D anisotropic function at the well location is upscaled into 3D by using local well tomography before they are propagated into the whole area of interest.Permalink: https://doi.org/10.1190/1.3628026FiguresReferencesRelatedDetailsCited ByWell calibrated angle-gather tomography for anisotropic model buildingPo Zhang, Daoliu Wang, Sheng Xu, Jinjun Liu, and Hongbo Zhou30 September 2020Near-surface and anisotropy modeling for efficient land seismic depth imaging in low-relief geologyDaniele Colombo, Ernesto Sandoval-Curiel, Mats Ris, and Salvarajah Seeni5 July 2017 | Interpretation, Vol. 5, No. 4Seismic velocity changes caused by an overburden stressValeri Korneev and Stanislav Glubokovskikh1 August 2013 | GEOPHYSICS, Vol. 78, No. 5 SEG Technical Program Expanded Abstracts 2011ISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2011 Pages: 4424 Publisher:Society of Exploration Geophysicists HistoryPublished: 08 Aug 2011 CITATION INFORMATION Huyen Bui, Robert Hubbard, Dave Watts, Chih‐Wen Kue, David Ng, and Mart Smith, (2011), "Incorporating well, rock physics, and geological information into anisotropy estimates enables a “true earth model”," SEG Technical Program Expanded Abstracts : 3928-3932. https://doi.org/10.1190/1.3628026 Plain-Language Summary PDF DownloadLoading ...

Methods are needed for treating aquaculture wastewater. The goal is to improve water quality sufficiently for it to be recycled to production ponds. One method is to use floating vegetation in treatment tanks. Alternatively, the floating vegetation could be grown directly on the production ponds. A study with floating vegetated mats for improving aquaculture wastewater quality is being conducted at the Univ. of GA Aquaculture Unit in Tifton, GA. The objective is to determine amount of biomass produced, nutrients removed, and quality of the treated wastewater. Wastewater from fish-production ponds is pumped into sets of 1285 L aquaculture tanks. There are three tanks in series in each treatment set, and three replicate sets per vegetative species. Each tank contains a floating platform (1 m2) for growth of vegetation. During a prototype test of wetland, horticultural, and agronomic plants, it was determined that cattail, iris, or soft rush were suitable for growing in aquaculture wastewater. The treatments are three-tank sets of cattail, iris, soft rush, or a control (no plants). The water is circulated every three weeks such that tank 1 receives water from the fish pond, tank 2 receives water from tank 1, tank 3 receives water from tank 2, and tank 3 is drained into a nearby storage pond. Water samples for analyses are collected from each tank prior to transfer to the next tank. Plant biomass is harvested as needed. Measurements are made of total biomass per tank and nutrient content (N, P, and K) of the plant tissue. Water quality measurements include N, P, K, BOD, chlorophyll, O2, turbidity, and pH. This paper presents partial results of the three-year study which started in May 2009.

A field study was conducted to determine nitrogen (N) mineralization from broiler litter (BL) in two Coastal Plain soils of differing texture, sandy (Tifton loamy sand) or clayey (Greenville sandy clay loam). These soils represented the broad range in surface textures commonly found in soils used for agricultural production in the southeastern Coastal Plain. Published protocols used for the study were designed by the ARS mineralization team. In addition to measuring ammonium (NH4-N) and nitrate (NO3-N) in the soil as a measure of N mineralization, both total C and total N were measured to determine the impact of a single BL amendment on C sequestration and N accumulation. Amounts of N in the soil from BL mineralization over 70 days were identical for both soils, 46.4 mg N kg-1 soil (0.046%), but differences occurred in timing of the mineralization processes. In the sandy Tifton soil, depletion of NH4-N and nitrification of the NH4-N to NO3-N occurred simultaneously. The NH4-N from the BL was depleted in 21 days while peak NO3-N concentrations in the soil were found at 28 days. In the clayey Greenville soil, NH4-N concentrations from BL mineralization increased for 21 days and then decreased until reaching background levels by 70 days. Nitrate concentrations never did increase in the BL amended Greenville soil, indicating both that the nitrification rate was much slower than the ammonification rate, and most likely, that what NO3-N was produced was lost from the soil by denitrification under wet conditions. The combination of soil textural and microclimate differences along with greater protection of the BL residues in the clayey soil than in the sandy soil are believed responsible for the observed N mineralization differences between the two soils. Previous research has shown that N mineralization rate is positively correlated with sand content and negatively correlated with clay content of soils, and the results of this study concurred with those findings. Measurements of total C and total N in both Coastal Plain soils showed that overall increases were small with a single BL amendment, and it was concluded that long-term studies are needed to investigate C sequestration and N accumulation. It was concluded from the study that there is a high probability that BL mineralization rates will be significantly slower on the more clayey Coastal Plain soils than on very sandy ones, and that farm managers should take these rates into consideration when planning timing and amounts of BL applications.

The U.S. Department of Agriculture Agricultural Research Service Southeast Watershed Research Laboratory (SEWRL) initiated a hydrologic research program on the Little River Experimental Watershed in south‐central Georgia, United States, in 1967. The primary intent of the program was to develop an improved understanding of basic hydrologic and water quality processes on Coastal Plain watersheds and to evaluate the effects of agricultural management practices on the region's natural resources and environment. Long‐term (up to 37 years), research‐quality streamflow data have been collected for up to eight flow measurement sites within the Gulf‐Atlantic Coastal Plain physiographic region, an important agricultural production area in the southeastern United States. Forty‐six precipitation gauges and three climate stations are currently in operation to collect data in support of the hydrologic network. Over the past 20 years, sediment and agrichemical concentrations in streamflow have also been monitored to permit evaluation of the impacts of agriculture on regional surface and groundwater quality. Along with the hydrologic and water quality data, geographic spatial data layers for terrain, soils, geology, vegetation, and land management have also been developed. These databases, described in five accompanying data reports, can be accessed via an ftp site supported by the SEWRL (ftp://www.tiftonars.org/).

Aerobic incubation methods have been widely used to assess soil nitrogen (N) mineralization, but standardized protocols are lacking. A single silt loam soil (Catlin silt loam; fine-silty, mixed, superactive, mesic, Oxyaquic Arguidoll) was subjected to aerobic incubation at six USDA-ARS locations using a standardized protocol. Incubations were conducted at multiple temperatures, which were combined based on degree days (DD). Soil water was maintained at 60% water-filled pore space (WFPS; constant) or allowed to fluctuate between 60 and 30% WFPS (cycle). Soil subsamples were removed periodically and extracted in 2M potassium chloride (KCl); nitrate (NO3) and ammonium (NH4) concentrations in extracts were determined colorimetrically. For each location, the rate of soil organic-matter N (SOMN) mineralization was estimated by regressing soil inorganic N (N-i) concentration on DD, using a linear (zero-order) model. When all data were included, the mineralization rate from four datasets was not statistically different, with a rate equivalent to 0.5 mg N kg(-1) soil day(-1). Soil incubated at two locations exhibited significantly higher SOMN mineralization rates. To assess whether this may have been due to pre-incubation conditions, time-zero data were excluded and regression analysis was conducted again. Using this data subset, SOMN mineralization from five (of six) datasets was not significantly different. Fluctuating soil water reduced N-mineralization rate at two (of four) locations by an average of 50%; fluctuating soil water content also substantially increased variability. This composite dataset demonstrates that standardization of aerobic incubation methodology is possible.

A water quality sampling program was initiated in 1974 by the U.S. Department of Agriculture Agricultural Research Service on the 334 km2 Little River Experimental Watershed (LREW) near Tifton in south Georgia to monitor the effects of changing land use and agricultural practices over time and to support development of simulation models capable of predicting future impacts of agricultural land use and management changes. Stream samples were taken on a weekly or more frequent basis and were analyzed for chloride, ammonium nitrogen, nitrate plus nitrite nitrogen, total kjeldahl nitrogen, total phosphorus, and dissolved molybdate reactive phosphorus. Monitoring began in 1974 on the entire watershed and four nested subwatersheds, ranging in size from 16.7 to 114.9 km2, and continues until present. Partial records of 7, 10, and 19 years exist for three additional subwatersheds. Suspended solids data are available for all eight subwatersheds for 1974–1978 and 1979–1981, three subwatersheds for 1982–1986, and all eight subwatersheds again beginning in the year 2000. The concentration and associated load data are being published on the LREW database anonymous ftp site (ftp://www.tiftonars.org/).

A farm-scale study was conducted from 2000 to 2004 to determine the effectiveness of grass-forest vegetated buffers in assimilating nitrogen (N) from overland flow application of swine lagoon effluent. The rationale for the study was that replicated buffer plot studies had shown that vegetated buffers will effectively assimilate N, but it was not known whether or not they would work at a larger scale. The study was conducted on a commercial farm near Tifton, Georgia. Wastewater was pumped from a single-stage anaerobic lagoon to vegetated buffers composed of grass and mature or newly planted pines. The buffers approximated 60 m in length by 90 m in width. The upper 10 m of each buffer was in grass, while the downslope area was in mature or newly planted pines. Six buffers were instrumented for wastewater application and water quality monitoring. Two buffers received wastewater at a 1X rate (600 kg N ha(-1) year(-1)), two at a 3/4X rate (450 kg N ha(-1) year(-1)), and two served as controls. The wastewater was applied to the 10 m grassed portion of the buffers. Transects of shallow groundwater wells starting at the grass-forest interface and running downslope were used to monitor water quality N. The study showed mixed results concerning N assimilation by the buffers. Upslope land use changes by the producer during the study added significant N inputs to one set of buffers, and they were unable to assimilate sufficient N from both these inputs and the wastewater to protect shallow groundwater quality. In contrast, almost all samplings of shallow groundwater under the buffers receiving N only from the overland flow applied swine lagoon effluent showed nitrate (NO3-N) concentrations 20 and 30 m downslope to be lower than 10 mg L-1 (drinking water standard). On these buffers, NO3-N concentrations in shallow groundwater were near background levels five years after wastewater application commenced. The study indicated that the ratio of buffer area width to wastewater application area width on the landscape should be at least 1:1, and that buffers for protection of water quality should be continuous oil the landscape. It was concluded from the study that buffers call be used at the farm scale to assimilate N from applied wastewater when they are sufficiently wide relative to waste application area, rate, and other N sources at the farm scale.

Broiler chicken (Gallus gallus) production is increasing rapidly in the southern Coastal Plain where there is an abundance of agricultural crops. The litter (mainly manure and bedding material) is a proven source of crop nutrients. We measured the pH, carbon (C), and extractable nutrient elements to a depth of go cm (3 ft) prior to and following seven years of an irrigated conservation-tilled double-cropped rotation. Litter was surface-applied to each crop at four rates (0, 4.5, 9.0, and 13.5 Mg ha(-1) yr(-1); 0, 2, 4, and 6 t(-1) ac(-1) yr(-1)) during the first five years of the rotation. Concentrations of extractable nutrient elements from the applied litter remained below levels of environmental concern during this seven-year study. Several trends in the data suggest that there will likely be problems with longer-term applications at high rates in the intensive crop rotation. Increases of extractable phosphorus (P), zinc (Zn), and copper (Cu) (contained in broiler feed) are of greatest concern. Phosphorus, extracted by Mehlich-1, increased >100 mg kg(-1) ( >100 ppm) in the surface soil due to the greatest BL rate. Many crops will thrive when soil P is high, but depending on slope and other soil properties, potential exists for losses of P via surface runoff or leaching. Such losses have been correlated with extractable P. Potassium from litter appeared to move to depths beyond the rooting zone of some crops. Concentrations of Cu increased four-fold and Zn five-fold in the top soil at the greatest rate of litter. Continuance of the applications at high rates will eventually lead to toxicity, particularly Zn toxicity in peanut (Arachis hypogaea L.). Nitrate-nitrogen concentration remained low through the soil profile. Potential benefits from broiler litter were attained by the maintenance of pH and an increase of 2.7 Mg C ha(-1) (1.2 t C ac(-1)) in the top 15 cm (6 in). Results of the study suggest that litter can be utilized well, without negative environmental effects when it is applied at conservative rates.

The National Program structure of USDA-ARS provides an opportunity to coordinate research on problems of national and global significance. A team of USDA-ARS scientists is conducting nationally coordinated research to develop predictions of manure N availability to protect water quality and improve farm solvency. Experimental design and research protocols were developed and used in common across all participating locations. Laboratory incubations are conducted at each location with a minimum of three soils, three temperatures, two wetting/drying regimes, and two manure treatments. A soil from the central United States (Catlin silt loam, fine-silty, mixed, superactive, mesic Oxyaquic Argiudoll) is used as an internal reference across all locations. Incubation data are compiled across locations to develop generalized predictions of manure nitrogen mineralization (Nmin). Field validation data are then obtained by monitoring nitrogen (N) transformations in manure-amended soil cores equipped with anion exchange resin to capture leached nitrate. This field data will be used to compare laboratory-based predictions with field observations of Nmin in each soil, climatic zone, and manure type represented. A Decision Support System will then be developed for predicting manure N mineralization across ranges in soil, climate, and manure composition. Protocols used by this research team are provided to 1) document the procedures used and 2) offer others detailed information for conducting research on nutrient transformation processes involving collaboration across locations or complementary research between laboratory and field environments.

Abstract The National Program structure of USDA‐ARS provides an opportunity to coordinate research on problems of national and global significance. A team of USDA‐ARS scientists is conducting nationally coordinated research to develop predictions of manure N availability to protect water quality and improve farm solvency. Experimental design and research protocols were developed and used in common across all participating locations. Laboratory incubations are conducted at each location with a minimum of three soils, three temperatures, two wetting/drying regimes, and two manure treatments. A soil from the central United States (Catlin silt loam, fine‐silty, mixed, superactive, mesic Oxyaquic Argiudoll) is used as an internal reference across all locations. Incubation data are compiled across locations to develop generalized predictions of manure nitrogen mineralization (Nmin). Field validation data are then obtained by monitoring nitrogen (N) transformations in manure‐amended soil cores equipped with anion exchange resin to capture leached nitrate. This field data will be used to compare laboratory‐based predictions with field observations of Nmin in each soil, climatic zone, and manure type represented. A Decision Support System will then be developed for predicting manure N mineralization across ranges in soil, climate, and manure composition. Protocols used by this research team are provided to 1) document the procedures used and 2) offer others detailed information for conducting research on nutrient transformation processes involving collaboration across locations or complementary research between laboratory and field environments.

ABSTRACT: Nitrogen (N) contamination of surface and groundwater is a health concern for both humans and animals. Excess nitrogen 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 have been shown to negatively affect the metabolism of domestic animals. Movement of NO3-N and NO2-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 nitrogen, is commonly practiced. Annual rainfall distribution often also requires use of supplemental irrigation. The combination of relatively high nitrogen 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 nitrogen 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 nitrogen transport and transport rates over a range of coastal plain soils and management scenarios. This paper examines the findings from these extensive studies, reports new findings from a long term study, and synthesizes all information to examine the long-term implications for nitrogen contamination of soil and water from agriculture in the southeastern Coastal Plain.

Grazing animals and pasture production can affect water quality both positively and negatively. Good management practices for forage production protect the soil surface from erosion compared with conventionally produced crops. Grazing animals and pasture production can negatively affect water quality through erosion and sediment transport into surface waters, through nutrients from urine and feces dropped by the animals and fertility practices associated with production of high-quality pasture, and through pathogens from the wastes. Erosion and sediment transport is primarily associated with high-density stocking and/or poor forage stands. The two nutrients of primary concern relating to animal production are N and P. Nitrogen is of concern because high concentrations in drinking water in the NO(3) form cause methemoglobinemia (blue baby disease), whereas other forms of N (primarily nitrite, NO(2)) are considered to be potentially carcinogenic. Phosphorus in the PO(4) form is of concern because it causes eutrophication of surface water bodies. The effect of grazing animals on soil and water quality must be evaluated at both the field and watershed scales. Such evaluation must account for both direct input of animal wastes from the grazing animal and also applications of inorganic fertilizers to produce quality pastures. Watershed-scale studies have primarily used the approach of nutrient loadings per land area and nutrient removals as livestock harvests. A number of studies have measured nutrient loads in surface runoff from grazed land and compared loads with other land uses, including row crop agriculture and forestry. Concentrations in discharge have been regressed against standard grazing animal units per land area. Watersheds with concentrated livestock populations have been shown to discharge as much as 5 to 10 times more nutrients than watersheds in cropland or forestry. The other major water quality concern with grazing animals is pathogens, which may move from the wastes into surface water bodies or ground water. Major surface water quality problems associated with pathogens have been associated with grazing animals, particularly when they are not fenced out from streams and farm ponds. This paper presents an overview of water quality issues relating to grazing animals.

Methods are needed to remove nutrients contained within wastewater lagoons. Potential exists for nutrient removal directly from lagoons if vegetation can be grown on floating mats in the lagoon and periodically harvested and removed. Vegetative cover of lagoons may also help reduce odor problems. A study was conducted to determine the feasibility of using floating mats of vegetation on swine lagoon wastewater. Wastewater from the University of Georgia swine wastewater lagoons was pumped to replicated tanks (1285 L) in which floating mats of vegetation were grown. The floating platforms were made of PVC pipe with attached wire screen and fibrous material into which the vegetation was sprigged. Three different wetland species were tested: cattail (Typha latifolia L.), soft rush (Juncus effuses), and maidencane (Panicum hematomon Schult 'Halifax'). Full-strength wastewater, 1/2-strength wastewater, and an inorganic nutrient solution (1/4-strength Hoaglund solution) as a control were tested. The test was conducted as a modified batch process as opposed to a continuous flow through process. The modification was that every two weeks half of the volume of each tank was replaced with the appropriate solution of full-strength wastewater 1/2-strength wastewater, or 1/4-strength Hoaglund solution so that nutrient concentrations would not be depleted. There were four replicate tanks of each nutrient solution for each wetland species, for a total of 36 tanks. Vegetation from the floating mats was harvested periodically by removing all vegetation above 5 cm of the base of the floating mat. Measurements were made at each cutting of the total biomass per tank, leaf area, and nutrient content (N, P K) of the vegetative tissue. Growth responses were quite different among the three species. The cattail had tremendous growth during the spring and summer months. The growth rate of the rush was slow for the first year It then died during summer of 2002 at both the 1/2-strength and full-strength wastewater, indicating that this species is not suitable for growth on floating mats in swine lagoon wastewater Total nutrient removal by both the cattail and maidencane was primarily a function of total biomass produced. Over the length of the study, on full-strength wastewater the cattail produced 16,511 g m(-2) biomass and removed 534, 79, and 563 g m(-2) of N, P and K, respectively, while the maidencane produced 9751 g m(-2) of biomass and removed 323, 48, and 223 g m(-2) of N, P and K, respectively. Results from this study indicate that potential exists for using floating platforms to grow cattail, maidencane, or possibly other yet to be identified plant species in wastewater lagoons for nutrient removal.

Information is needed on nutrient removal mechanisms in vegetated buffer systems to assist in the design of these tong-term nutrient removal systems. We determined nutrient removal by grass portions of grass-forest buffer systems receiving swine lagoon wastewater. Cuttings were made at three positions within buffers of coastal Bermuda grass (Cynondon dactylon L.) (Tifton 78) for three years. Wastewater was applied weekly at two rates. The first rate averaged 800 kg N ha(-1) yr(-1) (714 lb N ac(-1) yr(-1)), 215 kg P ha(-1) yr(-1) (192 lb P ac(-1) yr(-1)), and 1030 kg K ha(-1) yr(-1)(920 lb K ac(-1) yr(-1)), and the second rate furnished twice these amounts. Grass buffers 20 M (65.6 ft) in length removed 44% of the nitrogen (N), 19% of the phosphorus (P), and 23% Of the potassium (K) as grass biomass from the lesser wastewater application rate. Nutrient removal via uptake (percentage of applied) dropped by a factor of 1.6 when wastewater was applied at the greater rate. Overall, the study showed that while nutrient uptake into the grass biomass accounts for a portion of the nutrient removal in grass-forest buffer systems, the nutrient concentrations in surface runoff and subsurface water exiting these systems as reported previously (Hubbard et al., 1998b), imply that other factors (denitrification, forest uptake, and adsorption) play a greater role in the nutrient assimilation and filtering commonly associated with grass-forest buffer systems. The information on biomass production and nutrient removal by coastal Bermuda grass receiving wastewater in a lower landscape position is important for producers who want to utilize the wastewater nutrients and produce forage on an under-utilized portion of the landscape.