Effect of Grazing Management and Buffer Strips on Erosion from Pastures

Abstract

Excessive nutrient and sediment losses in runoff from pastures can lead to accelerated eutrophication. Several studies have shown that grazing management practices impact soil physical properties. Many studies have shown that rotational grazing can minimize soil compaction when compared to overgrazing, resulting in increased forage yields and vegetative cover. Improved forage growth reduces rainfall impact, increases infiltration rates, and prevents soil erosion. However, very limited information exists on the effects of grazing management on soil erosion. Likewise, few studies have shown the effects of buffer strips on sediment losses from grazed pastures. The objectives of this study were to evaluate the effects of grazing management practices on: (1) forage growth, (2) soil physical properties, (3) pasture hydrology, and (4) nutrient, metal, and sediment loads in runoff from pastureland receiving broiler litter. Field studies were conducted for seven years on 15 small watersheds (0.14 ha each). The soil series at this site are Enders (clayey, mixed, thermic, Typic Fragiudult) and Leadvale (fine silty, siliceous, thermic Typic Fragiudult), with Enders occurring at the top and Leadvale at the bottom of the slope. The watersheds were hydrologically isolated from each other and surrounded by earthen berms that were constructed with off-site soil. Barbed-wire fences were constructed on top of each of the berms. The base of each watershed narrowed to a point and was equipped with a covered 30.5 cm H-series fiberglass flume equipped with a pressure transducer for measuring runoff volumes. The transducer was connected to a housed automatic water sampler. The watersheds were hayed during year 1 when background data was collected. During years 2-7, five grazing-management strategies (GMS) were evaluated; (1) hayed, (2) overgrazed, (3) rotationally grazed, (4) rotationally grazed with an application buffer, and (5) rotationally grazed with a fenced riparian buffer. There were three replications per treatment in a completely randomized design. Broiler litter was applied during years 2-7 at a rate of 5.6 Mg ha-1. Soil bulk density increased as grazing pressure increased and was lowest under hayed conditions. Runoff volumes were highly correlated to bulk density. Percent cover and forage production were inversely related to stocking density, with hayed watersheds having the highest yields. Average annual sediment losses at the edge of field were 79.4, 70.9, 71.0, 37.1, and 26.5 kg ha-1 for overgrazed, rotationally grazed, rotationally grazed with buffer, rotationally grazed with fenced riparian buffer and hayfields, respectively. These results indicate that pasture management influences a wide range of parameters, including forage yields, hydrology, nutrient runoff, and soil erosion.