Submitted to: Animal, Agricultural and Food Processing Wastes Symposium
Publication Type: Proceedings
Publication Acceptance Date: 10/15/2003
Publication Date: 10/15/2003
Citation: Haan, M.M., Russell, J.R., Powers, W.J., Mickelson, S.K., Ahmed, S.I., Kovar, J.L., Schultz, R.C. 2003. Effects of grazing management on sediment and phosphorus in runoff. In: Prosser, Jr., P.J. (ed.). Proceedings Ninth International Symposium on Animal, Agricultural, and Food Processing Wastes, October 12-15, 2003. Raleigh, NC. p. 318-386. Interpretive Summary: The amounts of sediment and phosphorus (P) in surface runoff from agricultural lands are of concern because of the potential for siltation and eutrophication of waterways. Because of current problems, it is likely that the U.S. Environmental Protection Agency will implement regulations to control the total maximum daily loads of nutrients in watersheds in the near future. At this time, there is limited information on total sediment and P losses in runoff from pastureland in the Midwest. Because aboveground biomass limits soil disruption caused by the impact of raindrops and roots hold soil particles, forages harvested at an appropriate height through suitable grazing management should promote water infiltration and minimize sediment and P loss in runoff water from pastures. The purpose of this study is to quantify the amounts of sediment and P in surface runoff from Iowa pasturelands managed by different systems, develop tools to monitor and control sediment and P transport from pastures, and develop best management practices for producers to control sediment and P losses, while optimizing forage productivity. After two years, we found that by practicing good forage management techniques, the amounts of sediment and nutrients coming off of pastureland can be controlled. Practices such as the use of buffer strips around waterways and rotational grazing of cattle can greatly reduce degradation of surface water resources. The results of this research will provide useful information to cattle producers, local environment groups, and Cooperative Extension and Natural Resources Conservation Service personnel.
Technical Abstract: In spring 2001 (year 1) and 2002 (year 2), three blocks of five 0.4-ha paddocks were grazed by beef cows on hills at the Iowa State University Rhodes Research and Demonstration Farm to determine the effects of grazing treatment on nutrient and sediment loss from pastureland. Grazing management treatments included an ungrazed control, summer hay harvest with winter stockpiled grazing, continuous stocking to a residual height of 5 cm, rotational stocking to a residual height of 5 cm, and rotational stocking to a residual height of 10 cm. At four times (late spring, mid-summer, autumn and early the subsequent spring) in each year, rainfall simulations were conducted at 6 sites within each paddock and 6 sites in a buffer zone down slope from each paddock. Rainfall simulators dripped at a rate of 7.1 cm/hour over a 0.5-m**2 area for a period of 1.5 hours. Runoff was collected and analyzed for total sediment, total phosphorus, and dissolved phosphorus. Simultaneous to each rainfall simulation, measurement was taken of ground cover, penetration resistance, surface roughness, slope, the contents of phosphorus and moisture of the soil, and the sward height and mass of forage. Losses of sediment, total P, and soluble P were greater from grazed paddocks than ungrazed paddocks in year 1. However, in year 2, losses of sediment, total P, and soluble P from paddocks grazed by rotational stocking to a sward height of 10 cm or harvested as hay during the summer and grazed during winter did not differ from ungrazed paddocks. In both years total P losses from the buffer area immediately or 10 m below the paddocks were lower than within the paddocks. Of the physical measurements, the proportion of ground cover was most highly related to sediment loss. Soil Bray-1 P concentrations did not differ between treatments, but are related to the losses of total and soluble P. Results imply that sediment and phosphorus losses in pasture runoff may be reduced by managing rotational stocking to maintain adequate sward height and/or using vegetative buffer strips along pasture streams. Such management practices are particularly important in pastures on soils with high Bray-1 P concentrations.