Grazing Management Effects on Sediment and Phosphorus in Surface Runoff
Abstract
Sediment and phosphorus (P) in runoff from pastures are potential non–point-source pollutants in surface waters that may beinfluenced by surface cover, sward height, treading damage, surface slope, soil moisture, and soil P. The objectives of the currentstudy were to quantify sediment and total P loads in runoff produced during simulated rainfall from pastures and to evaluatetheir relationships with the physical and chemical characteristics of the soil and sward. Five forage management treatments—ungrazed (U), hay harvest/fall stockpile grazing (HS), continuous stocking to a sward height of 5 cm (5C), and rotationalstocking to sward heights of 5 (5R) or 10 (10R) cm—were established in triplicate 0.40-ha paddocks in 3 smooth bromegrass(Bromus inermisLeyss.) pastures for 3 years. Rainfall simulations were conducted at a rainfall intensity of 7.1 cmh1for1.5 hours over a 0.5-m2area in 3 locations at 2 slope ranges in each paddock in June, August, and October of each year and thesubsequent April. Forage management did not affect mean sediment load (7.365.0 kgha1h1). Mean total P load was greatest from 5C treatment (0.07160.011 kgha1h1), did not differ among the U, HS, and 10R treatments(0.01960.011 kgha1h1), and was intermediate in the 5R treatment (0.05360.011 kgha1h1). Of the soil and swardcharacteristics measured, percentage surface cover was most highly related to sediment load (R2¼0.16) and total P load(R2¼0.10). Surface runoff from pastures managed to maintain adequate residual forage cover did not contribute greatersediment or P to surface waters than an ungrazed grassland