Animal waste management plans are developed to minimize negative impacts on water quality. These plans are based upon the use of agronomic rates which guide the timing and amount of animal waste applied. Although current agronomic rates are available, updated values based on research are needed. Because the majority of animal waste management plans involve the use of forage grasses, agronomic rates need to be updated and yield data must include emerging forage species. In addition, historical data on agronomic rates have been obtained without the large amount of water, phosphorous, and potassium associated with effluent application. Relevant data which includes supplemental irrigation, phosphorous, and potassium are needed.

The specific objectives of this work are to:

1. Demonstrate effect of various rates of nitrogen loading on forage dry matter production, nitrate levels in forage, and levels of inorganic soil nitrogen.
2. Demonstrate effects of various rates of animal waste application on phosphorous, copper, zinc, sodium, and potassium accumulation in forages.
3. Use demonstration site to verify and produce an RYE database for these forage systems.
4. Educate farmers and agricultural agency personnel on recommended rates for application of swine effluent, which are supported by adequate research data.
5. Demonstrate effects of inorganic fertilizer and animal waste as nitrogen sources.
6. Disseminate information to swine producers and other interested parties.

Maintaining and improving water quality is a goal of all North Carolina citizens, including those involved in swine production. Swine waste management systems often include the use of swine lagoon effluent in the production of forages. In the past, application rates have been based on the estimated values of nutrient uptake and historical crop yield data. However, as swine producers experience increased regulation and public scrutiny, it is important to ensure that the agronomic rates are scientifically verified.

The use of the realistic yield expectation (RYE) principle involves the application of nitrogen at a rate that minimizes the potential for nitrate leaching. Swine producers and agricultural agency personnel have requested up-to-date information on RYE values and the associated N fertilization rates that are based on plant available nitrogen.

Some producers have indicated that the two standard forage crops, tall fescue and bermudagrass overseeded with rye, can utilize more N than that which is currently recommended by agricultural agencies. Other species require initial research to develop recommendations that are specific to the crop and based on scientific research, rather than an estimated N uptake value based on other standard forage crops. These crops, prairiegrass (matua), crabgrass, and gamagrass, must be examined in a field experiment which includes the standard crops, bermudagrass/rye, and tall fescue.

The development of agronomic application rates for swine effluent has been largely based on the response of crops to inorganic fertilizer and not swine waste, nor the large amounts of water and phosphorous that are associated with effluent application. Furthermore, the application of a PAN coefficient to the total N content of swine waste has been primarily based on lab studies. This work will provide a side-by-side comparison of swine effluent and inorganic fertilizer sources. The cycling of nitrogen in the plant-soil system will be adequately monitored by determining forage dry matter accumulation, forage N concentration, forage nitrate content, and inorganic and organic pools of soil N. These data will be used to develop RYE values which will minimize the impact of land application of swine effluent on water quality.

Forage crops may be able to utilize a large amount of nitrogen, but application rates must consider the effect of these high rates on nitrate concentration in the forage. Excessive N fertilization rates may cause high levels of nitrate in harvested forage which can be harmful to ruminant livestock. Forages with nitrate levels below 0.4% NO₃-N are considered safe for ruminant consumption but many instances of nitrate concentration greater than 0.4% were reported in 1997, primarily in hays harvested from swine production facilities. Excessive nitrate levels in hay can greatly limit the economic value as a forage for ruminant livestock.

Although nitrogen (N), is currently the priority element, it is important to monitor other constituents of swine effluent such as phosphorous (P), copper (Cu), and zinc (Zn). Soil scientists with NCSU and the NCDA have become increasingly concerned about P loading to fields receiving animal waste. For this reason it is important to monitor phosphorous, especially under the high fertilization rate. In addition, Cu and Zn are important because in high concentrations they may be toxic to plant growth. This work will provide information on P, Cu, and Zn at the initiation and termination of this experiment. Provided that additional funds can be obtained in future years, this site will provide valuable information regarding the long-term accumulation of P, Cu, and Zn in Coastal Plain soils and any associated effects on water quality.

Location of the demonstration will be at a Coastal Plain site of the Caswell Farm in Kinston, NC. This NC Department of Agriculture Farm is strategically located within 50 miles of seven of the top ten counties for swine production. This site offers exceptional opportunities for field days addressing swine producers in the Neuse, Tar Pamlico, and Cape Fear river basins.

The design of the demonstration will be a split-split-plot with factors of forage species, N source, and N rate (Table 1). The forage species in this project will be prairiegrass (matua), crabgrass overseeded with cereal rye, bermudagrass overseeded with cereal rye, gamagrass, and tall fescue. Although crabgrass and gamagrass are both emerging warm season crops, only crabgrass will be overseeded with rye because gamagrass is not an appropriate crop for overseeding with cereal rye.