The Poultry Litter Land Application Rate Study – Assessing the Impacts of Broiler Litter Applications on Surface Water Quality

McBroom, M.W., Young, J.L.

Poultry production in the United States has grown dramatically in recent years which has resulted in the generation of large quantities of poultry litter. The high nutrient content of poultry litter makes it an excellent soil nutrient amendment. However, concern has arisen regarding potential negative impacts on stream water quality. Numerous studies have evaluated the edge of field effects of litter applications through plot studies while others have evaluated instream effects. However, an integration of both instream (watershed scale) as well as edge of field (plot studies) effects of litter applications on water quality was needed. Beginning in 1994, four related studies were conducted in East Texas by Stephen F. Austin State University, the Texas Commission on Environmental Quality, and the Angelina Neches River Authority to determine these potential effects. This project included: 1) a study to determine the effects on runoff water quality from 12 experimental plots with four different rates of surface litter application, 2) an upstream/downstream stream gaging study to evaluate water quality of two tributary streams of the Attoyac Bayou in areas of intense poultry production, 3) an assessment of water quality conditions within the Attoyac Bayou, 4) the use of a computer simulation model (AGNPS) to determine possible water quality effects of litter applications in the study areas. Storm water samples collected from the runoff plots and watershed gaging stations were analyzed for nutrients (total phosphorus, orthophosphorus, nitrate-nitrogen, Total Kjeldahl nitrogen, and potassium), total suspended sediment, pH, and conductivity. At watershed gaging stations, weekly grab samples were also collected and analyzed for the above parameters along with dissolved oxygen, temperature, and bacteria. Surface plot data indicated that a vegetated filter strip of 4.5 m was effective in reducing nutrient losses at the edge of fields where litter is applied, though buffer effectiveness was seen to decline after multiple applications of litter at higher rates. For the stream sampling sites, significantly higher nitrogen concentrations were found from pastured sites receiving broiler litter than from upstream forested sites. However, these concentrations were still below levels that could result in adverse water quality impacts and likely result from multiple nonpoint pollution sources in the pastured watershed. Bacterial concentrations were higher in pastured watersheds, though significant contributions resulted from wildlife in the forested watersheds as well. Results from these studies indicate that with proper management, including the use of streamside buffers and appropriate application rates, poultry litter applications are not likely to result in water quality degradation in the Attoyac Bayou.