Title: Managing Broiler Litter Application Rate and Grazing to Decrease Watershed Runoff Losses Authors
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 19, 2007
Publication Date: March 5, 2008
Citation: Sistani, K.R., Brink, G.E., Oldham, J.L. 2008. Managing Broiler Litter Application Rate and Grazing to Decrease Watershed Runoff Losses. Journal of Environmental Quality. 37:718-724 Interpretive Summary: Runoff from manured grazing and haying pastures has the potential to transport nutrients to nearby surface water. Nonpoint-source pollution of water bodies during the past 20 years has received global attention. It has been reported that over 11.4 million tons of broiler litter was generated in 1996, of which over 90% was land applied. Poultry litter is generally surface applied to pastures and hay fields to supply plant nutrients, particularly nitrogen (N) and phosphorus (P). Proper land application of animal manure is critical to water quality in watersheds with significant poultry and livestock numbers. Nutrient transport risk from land applied manure to surface water depends on the interaction of intrinsic site properties, climate, and pasture management. With regard to permanent pasture systems, inability to incorporate waste materials leads to increased nutrient concentration, such as P, Cu, and Zn near the soil surface. The objective of this study was to determine the impact of pasture management (grazing, haying, combined grazing/haying, and cropping system) and broiler litter application rate (N vs. P basis) on surface runoff nutrients exiting bermudagrass paddocks. The inorganic N content of the runoff exiting grazed or grazed/hayed (combination of grazing ryegrass and haying bermudagrass) paddocks with litter applied on N basis were greater than the same treatments that received litter on P basis. All the treatments that received broiler litter on N basis had greater total P and total dissolved P in the runoff water. The mean total P loss per runoff event ranged from 7 to 45 g ha-1, and the grazed treatment with litter applied on N basis had the most. Total dissolved P was the dominant P fraction in the runoff ranging from 85% to 93% of the total P. Our results indicate that litter may be applied on N basis if the soil P is low and the pasture is being hayed. In contrast, grazing is recommended if litter applied on P basis.
Technical Abstract: Pasture management and broiler litter application rate are critical factors influencing the magnitude of nutrients being transported by runoff from fields. This study was conducted to investigate the impact of pasture management (haying, grazing, and a haying and grazing combination) and broiler litter application rate (N vs. P basis) on nutrient runoff from common bermudagrass [Cynodon dactylon (L.) Pers.] pastures. The experiment was conducted on a Ruston fine sandy loam with a factorial arrangement (the treatments were a 3 x 2 factorial; 3 harvesting treatments and 2 litter application rates with a control) replicated three times on 21 paddocks ranging from 0.10 to 0.70 ha. Runoff water was collected from natural rainfall events from 2001 to 2003. Runoff water and soil samples were analyzed for nutrients and sediments. Forty eight rainfall events during the study generated sufficient runoff for analysis. Runoff was generally greater (29%) from grazed than hayed pastures regardless of the litter application rate. There was higher inorganic N in the runoff from grazed paddocks when litter rate was based on N rather than P. The mean total P loss per runoff event for all treatments ranged from 7 to 45 g ha-1 and the grazed treatment with litter applied on N basis had the greatest total P loss. Total dissolved P was the dominant P fraction in the runoff, ranging from 85% to 93% of the total P. The soluble reactive P was greater for treatments with litter applied on N basis regardless of pasture management. Runoff total sediments were greater for N-based litter application compared to those which received litter on P basis. Our results indicate that litter may be applied on N basis if the pasture is hayed and the soil P is low. In contrast, litter rates should be based on a P-basis if pasture is grazed.