Sediment and phosphorus (P) in runoff from pastures are potential non–point-source pollutants in surface waters that may be influenced by surface cover, sward height, treading damage, surface slope, soil moisture, and soil P. The objectives of the current study were to quantify sediment and total P loads in runoff produced during simulated rainfall from pastures and to evaluate their 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 rotational stocking to sward heights of 5 (5R) or 10 (10R) cm—were established in triplicate 0.40-ha paddocks in 3 smooth bromegrass (Bromus inermis Leyss.) pastures for 3 years. Rainfall simulations were conducted at a rainfall intensity of 7.1 cm·h−1 for 1.5 hours over a 0.5-m2 area in 3 locations at 2 slope ranges in each paddock in June, August, and October of each year and the subsequent April. Forage management did not affect mean sediment load (7.3 ± 5.0 kg·ha−1·h−1). Mean total P load was greatest from 5C treatment (0.071 ± 0.011 kg·ha−1·h−1), did not differ among the U, HS, and 10R treatments (0.019 ± 0.011 kg·ha−1·h−1), and was intermediate in the 5R treatment (0.053 ± 0.011 kg·ha−1·h−1). Of the soil and sward characteristics measured, percentage surface cover was most highly related to sediment load (R2 = 0.16) and total P load (R2 = 0.10). Surface runoff from pastures managed to maintain adequate residual forage cover did not contribute greater sediment or P to surface waters than an ungrazed grassland.
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Vol. 59 • No. 6