Long-term effects of grazing management and buffer strips on phosphorus runoff from pastures fertilized with poultry litter.

Phosphorus (P) runoff from pastures can cause accelerated eutrophication of surface waters. However, few long-term studies have been conducted on the effects of best management practices, such as rotational grazing and/or buffer strips on P losses from pastures. The objective of this study was to evaluate the long-term effects of grazing management and buffer strips on P runoff from pastures receiving annual (5.6 Mg ha ) poultry litter applications. A 14-yr study was conducted on 15 small watersheds (0.14 ha) with five treatments: hayed (H), continuously grazed (CG), rotationally grazed (R), rotationally grazed with an unfertilized buffer strip (RB), and rotationally grazed with an unfertilized fenced riparian buffer (RBR). Runoff samples were collected using automatic samplers during runoff events. Average annual runoff volumes from H (40 mm yr ) and RBR (48 mm yr ) were lower than CG and RB, which were both 65 mm yr , and from R (67 mm yr ). Rotational grazing alone did not reduce P loads compared with continuous grazing (1.88 and 1.71 kg P ha for R and CG, respectively). However, compared with CG, total P losses from RB pastures were reduced 36% with unfertilized buffer strips (1.21 kg P ha ), 60% in RBR watersheds with unfertilized fenced riparian buffer strips (0.74 kg P ha ), and 49% by converting pastures to hayfields (0.97 kg P ha ). Hence, the use of unfertilized buffer strips, unfertilized fenced riparian buffer strips, or converting pastures to hayfields are effective best management practices for reducing P runoff in U.S. pasture systems.