Title: Efficient crop utilization of nutrients contained in swine lagoon effluent

Leaders: Dr. Noah N. Ranells, Dr. James T. Green, Dr. Matt. H. Poore, Dr. Jim C. Barker

Department: Crop Science, Animal Science, Biological and Agricultural Engineering

Supported by: NC Pork Council

Period: July 1998 June 2001



Modern swine production facilities in North Carolina produce large amounts of liquid waste as lagoon effluent. Agronomic utilization of this waste for crop, hay, and pasture production has been a common practice for swine producers in the Coastal Plain region. Standard practices have involved the land application of waste to receiving crops such as tall fescue or bermudagrass overseeded with cereal rye. Although, application rates have been based on the estimated values of nutrient uptake and historical crop yield data, up-to-date research data is not available.

Farmers are responding to the issue of water quality and making an effort to improve animal waste management. Many swine producers are requesting agronomic rate information for other crops such as rescuegrass (matua), crabgrass, and gamagrass. Some of these crops may have the potential to increase nitrogen (N) uptake and further minimize nitrate leaching. This overall goal of this project is to develop scientifically verified recommendations for the optimal management of N contained in animal wastes that are applied to conventional and emerging forage crops.


Goals and Objectives


  1. Determine appropriate rates of nitrogen loading for each forage treatment based on dry matter production, nitrate levels in forage, and levels of inorganic soil nitrogen.
  2. Document phosphorous, copper, and zinc accumulation in forages.
  3. Produce an RYE database for these forage systems.
  4. Develop recommended rates for application of swine effluent supported by adequate research data.
  5. Compare effects of inorganic fertilizer and animal waste as nitrogen sources.
  6. Disseminate information to swine producers.


Rationale and Significance

The use of swine lagoon effluent in the production of forages is a common practice associated with pork production in North Carolina. Currently, application rates are based on the estimated values of nutrient uptake and historical crop yield data (NCCES, 1997). However, as swine producers experience increased regulation and public scrutiny it is important to ensure that the agronomic rates are scientifically verified.

Swine producers and agricultural agency personnel have requested up-to-date information on realistic yield expectation (RYE) values and the associated N fertilization rates on a plant available nitrogen (PAN) basis. 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, rescuegrass (matua), crabgrass, and gamagrass, must be examined in a field experiment which includes the standard crops, bermudagrass overseeded with cereal rye and tall fescue.

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 0.25% NO3-N are considered safe for ruminant consumption, while nitrate levels greater than 1.5% are considered toxic to livestock (Ball et al. 1991). In North Carolina, many instances of nitrate concentration greater than 0.4% were reported in 1997, primarily in hays harvested from swine production facilities. Careful management is required, when feeding livestock forage that contains nitrate levels in the range of 0.25% to 1.50%. Based on this information, it is clear that excessive nitrate levels in hay can greatly limit the economic value as a forage for ruminant livestock.

Although 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 (Brady, 1984). 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.

Experimental Plan

The experiment will be conducted at two locations in the Coastal Plain. One site will be the Horticultural Crops Research Station in Clinton, NC. This location is strategically located in Sampson County which is ranked second in the state for swine production. This site offers exceptional opportunities for field days addressing swine producers in the Neuse and Cape Fear river basins.

The experimental design 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 rescuegrass (matua), crabgrass overseeded with cereal rye, bermudagrass overseeded with cereal rye, gamagrass, and tall fescue. Although crabgrass and gamagrass are both warm season crops, only crabgrass will be overseeded with rye because gamagrass is not an appropriate crop for overseeding with cereal rye.

Table 1. Experimental Design



N Source

N Rates







Tall fescue


Swine effluent

Inorganic fertilizer







Four (two soil series)


Plot Size

15 by 30 feet