Submitted to: American Forage and Grassland Council Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/17/2002
Publication Date: 7/17/2002
Citation: HAAN, M.M., RUSSELL, J.R., POWERS, W.J., MICKELSON, S.K., KOVAR, J.L., SCHULTZ, R.C. EFFECTS OF GRAZING MANAGEMENT ON SEDIMENT AND PHOSPHORUS RUNOFF. AMERICAN FORAGE AND GRASSLAND COUNCIL PROCEEDINGS. 2002. V. 11. P. 292-296. 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 Iowa's 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 objectives of this experiment are to quantify the amounts of sediment and P in surface runoff from 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. Early results indicate 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 environmental groups, and Cooperative Extension and NRCS personnel.
Technical Abstract: In spring 2001, grazing treatments were initiated on pastures at the Iowa State University Rhodes Research Farm to determine the effects of grazing management on nutrient and sediment loss from pastureland. Treatments included an ungrazed control, summer hay harvest with winter stockpiled grazing, continuous stocking to a residual height of 2 in., rotational stocking to a residual height of 2 in., and rotational stocking to a residual height of 4 in. In three months (June, August and October) during the 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 2.8 in./h over a 5.4-ft**2 area for a period of 1.5 h. Amounts of rainfall and runoff were recorded at 10-min. intervals during the sampling period. Runoff was collected and analyzed for total sediment, total P, and dissolved P. Simultaneous to each rainfall simulation, measurements were taken of ground cover, penetration resistance, surface roughness, slope, soil water content, total soil P, and the sward height and mass of forage. Slope and forage treatment in paddocks did not significantly affect the concentration and amount of sediment in runoff. However, the concentrations and amounts of total P in runoff from paddocks that were grazed were greater than paddocks that were ungrazed or harvested for hay during summer. The concentrations and amounts of total P in runoff were lower in paddocks that were rotationally stocked to a height of 4 in. than in those that were rotationally stocked to 2 in. The amounts of sediment and total P in runoff from paddocks that were grazed were greater than their respective buffers.