Research ArticlesGrazing Management Effects on Sediment and Phosphorus in Surface Runoff
Section snippets
INTRODUCTION
Erosion of sediment and transport of nutrients in surface runoff are natural processes that may be accelerated by land management practices (Smeck 1985). Soil losses from forage systems are generally low (Gard et al. 1943) because of improved soil structure (Entz et al. 2002), increased soil microporosity (McDowell et al. 2003), rainfall infiltration (Alderfer and Robinson 1947), protection of soil surface from raindrop impact (Pearce et al. 1998), and filtration of sediment from surface runoff
Site Description
For 3 years, 2001–2003, pastures located at the Iowa State University Rhodes Research and Demonstration Farm (lat 42°00′N, long 93°25′W) were managed to determine the impacts of beef cow grazing on sediment and P losses in surface runoff from pastures. Pastures had slopes of 0°–15° and were primarily composed of smooth bromegrass (Bromus inermis Leyss). Soils at the study site were characterized as Downs silt loam (fine-silty, mixed, mesic Mollic Hapludalf), Gara loam (fine-loamy, mixed, mesic
Treatment Effects
Forage management practices that maintain high levels of soil organic matter, litter, and vegetative cover have been shown to improve rainfall infiltration (Naeth et al. 1990). No surface runoff was generated during 44.8% ± 5.1% of rainfall simulations conducted in the U treatment, which did not differ from the 10R (31.6% ± 5.1%) treatment, and was greater (P < 0.05) than the number of simulation events, which did not generate runoff in the HS (19.5% ± 5.1%), 5R (16.7% ± 5.1%), and 5C
MANAGEMENT IMPLICATIONS
Some sediment and P loss will occur in surface runoff from pastures, even in the absence of forage harvest by either grazing or hay harvest. Losses can be accelerated by forage harvest by grazing or hay harvest. Forage management practices that leave adequate forage residue on the surface, such as the 10R and HS treatments in smooth bromegrass pastures, will improve infiltration rate and protect the soil surface from the force of raindrops impacting the soil surface. These factors will result
Acknowledgments
The authors would like to thank the numerous graduate and undergraduate students who assisted with data collection and analysis and the staff at the Iowa State University Rhodes Research Farm for assistance with animal management.
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Research was funded, in part, by the Iowa Agricultural and Home Economics Experiment Station, Ames, IA, and by grants from the Iowa Dept of Natural Resources, Iowa State University Leopold Center for Sustainable Agriculture, and the Iowa State Water Resources Research Institute.