Grazing management and buffer strip impact on nitrogen runoff from pastures fertilized with poultry litter

Authors: PILON, CRIS - University Of Georgia; Moore, Philip; Pote, Daniel; Martin, Jerry; Owens, Phillip; Ashworth, Amanda; MILLER, DAVID - University Of Arkansas; DELAUNE, PAUL - Texas A&M Agrilife

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2018
Publication Date: 8/9/2018
Citation: Pilon, C., Moore Jr, P.A., Pote, D.H., Martin, J.W., Owens, P.R., Ashworth, A.J., Miller, D.M., Delaune, P.B. 2018. Grazing management and buffer strip impact on nitrogen runoff from pastures fertilized with poultry litter. Journal of Environmental Quality. Available: https://dl.sciencesocieties.org/publications/jeq/abstracts/0/0/jeq2018.04.0159.

Interpretive Summary: Nitrogen (N) runoff from pastures can cause serious water quality problems. Poultry litter is a relatively cheap fertilizer and a good source of nutrients, like N, however, applications of poultry litter to pastures can result in excessive N in runoff water. The objective of this research was to determine the long-term effects of different grazing management strategies and buffer strips on N runoff from pastures fertilized with poultry litter. A 12-yr study was conducted using 15 small watersheds in Booneville, AR. There were five different treatments: continuous grazing (CG), hayed (H), rotational grazing (R), rotational grazing with an unfertilized buffer strip (RB), and rotational grazing with a fenced unfertilized riparian buffer (RBR). Poultry litter was surface applied each year at a rate of 5.6 Mg ha-1. Concentrations and loads of total N (TN), NO3-N, NH4-N, organic N and total organic carbon (TOC) in runoff varied considerably and were related to precipitation trends. Most of the N in runoff was organic N. Rotational grazing resulted in the highest concentrations and loads of N in runoff. Total organic C concentrations and loads in runoff were also higher from rotationally grazed watersheds than all other treatments. These results were surprising since rotational grazing is generally considered a best management practice (BMP) which reduces soil erosion and improves soil health. Nitrogen runoff from rotationally grazed pastures was reduced by 44% with unfertilized buffer strips and by 54% with fenced unfertilized riparian buffers. Converting pastures to hayfields also resulting in significantly less N runoff.

Technical Abstract: Nitrogen (N) runoff from grazed pastures can result in accelerated eutrophication. Poultry litter is a low-cost fertilizer source for nutrients such as N, however, applications of poultry litter to pastures can result in excessive N in runoff. The objective of this study was to evaluate the long-term effects of grazing management and buffer strips on N runoff from pastures fertilized with poultry litter. A 12-yr study was conducted on 15 small watersheds in Booneville, AR using five management practices: continuous grazing (CG), hayed (H), rotational grazing (R), rotational grazing with an unfertilized buffer strip (RB), and rotational grazing with a fenced unfertilized riparian buffer (RBR). Poultry litter was applied annually at a rate of 5.6 Mg ha-1. Concentrations and loads of total N (TN), NO3-N, NH4-N, organic N and total organic carbon (TOC) in runoff varied intra and inter-annually and coincided with precipitation trends. Overall, greatest component of TN in runoff was organic N. Rotational grazing resulted in the highest concentrations and loads of all forms of N in runoff when compared to the other treatments, including continuous grazing. Total organic C concentrations and loads in runoff were also higher from rotationally grazed watersheds than all other treatments. These results were unexpected and difficult to explain since rotational grazing is considered a best management practice (BMP) which typically reduces soil erosion and increases soil organic C. Nitrogen runoff losses from rotationally grazed pastures were reduced by 44% with unfertilized buffer strips and by 54% with fenced unfertilized riparian buffers. Converting pastures to hayfields also resulting in less N runoff.