Submitted to: Agricultural and Environment Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/6/2002
Publication Date: 3/6/2003
Citation: POWERS, W., RUSSELL, J., HAAN, M., SCHULTZ, R., STAUFFER, E., ZAIMES, G., HUNKINS, B., KOVAR, J.L., BOEHM, J., MICKELSON, S. GRAZING SYSTEMS TO MAXIMIZE FORAGE AND MINIMIZE P, N, AND SEDIMENT POLLUTION OF STREAMS. AGRICULTURAL AND ENVIRONMENT CONFERENCE PROCEEDINGS. 2003. P. 23-35. Interpretive Summary: Although degradation of waterways in Iowa is of great concern, information on the amount of sediment and phosphorus leaving pastureland in runoff water is quite limited. Because the foliage of pasture grasses covers the soil and the roots keep soil particles from washing away when it rains, proper management of grazing by cattle is necessary to minimize sediment and phosphorus losses. In spring 2001, a field study was initiated in which we measured sediment and phosphorus losses in runoff water from various grazing management practices on pastures at the ISU Rhodes Research Farm, as well as on privately-owned land in four Iowa Counties. At this early stage of the project, few conclusions can be drawn. However, preliminary numbers suggest that movement of sediment and phosphorus in runoff water are tremendously affected by the amount of moisture in the soil and the height of the grass in the pasture when it begins to rain. These two variables, therefore, will need to be considered in the development of grazing management systems that minimize losses from pastures.
Technical Abstract: The amount of sediment and phosphorus in surface runoff from agricultural lands is of concern because of the potential for siltation and eutrophication of Iowa's waterways. Currently, there is limited information on total sediment and phosphorus loads in surface runoff coming from pastureland in the Midwest. Because foliage of forage limits soil disruption caused by the impact of raindrops and forage roots hold soil particles, forages harvested at an appropriate height through suitable grazing management should maintain water infiltration and minimize sediment and phosphorus losses in surface runoff from pastures. The purpose of this field study was to quantify sediment and phosphorus loss in surface runoff from various upland and riparian grazing management practices. At this early stage of the project, few conclusions can be drawn. However, data suggest that rainfall infiltration rate and thus, sediment and phosphorus flow are highly affected by the ambient soil moisture concentration and sward height. These two variables, therefore, will need to be considered in the development of grazing management systems that minimize sediment and nutrient losses from pastures. Management-specific models that describe phosphorus excretion and movement as a function of animal performance and grazing system may result and serve as part of the development process for Comprehensive Nutrient Management Plans.