Long-Term Study on the Effects of Buffer Strips and Grazing Management on Phosphorus Runoff from Pastures Fertilized with Poultry Litter.

Phosphorus (P) runoff from pastures receiving poultry litter can cause eutrophication of surface waters. However, few long-term studies have evaluated the effects of rotational grazing and/or buffer strips on P losses from pastures. The objective of this study was to measure the long-term effects of grazing management and buffer strips on P runoff from pastures fertilized with poultry litter. A 15 year study was conducted utilizing 15 instrumented paddocks (0.14 Ha each) in Booneville, AR. There were five management schemes: hayed (H), continuously grazed (CG), rotationally grazed (R), rotationally grazed with an unfertilized buffer strip (RB), and rotationally grazing with an unfertilized fenced riparian buffer (RBR) with three replications per treatment in a completely randomized design. Each paddock was fenced and hydrologically isolated with earthen berms and equipped with flumes and automatic water samplers which sampled runoff from each event during the 15 year period. All of the fields were fertilized with poultry litter at a rate of 5.6 mg ha^-1 each year in spring. Phosphorus concentrations and P loads in runoff varied annually, coinciding with trends in precipitation. Soluble reactive P was the dominant form of P in runoff and comprised about 80% of the total. Average flow-weighted total P concentrations in runoff water from CG and R paddocks were not significantly different (3.09 and 2.60 mg P L^-1, respectively); however, they were higher than that from H, RB, and RBR (2.02, 1.77, and 1.50 mg P L^-1, respectively). Rotational grazing did not significantly reduce P loads when compared to continuous grazing (1.66 and 1.76 kg P ha^-1 for R and CG, respectively). Total P loads from RB pastures were reduced by 32% with unfertilized buffer strips, by 56% in RBR paddocks with unfertilized fenced riparian buffer strips, and by 44% by converting pastures to hayfields.