Runoff from open beef feedlots is a contributor of nutrients to the surface waters of Iowa. Currently, efforts are underway to improve the runoff control systems on open feedlot operations of all sizes. Both the Iowa Small Feedlot Team (comprised of ISU faculty and staff, Iowa DNR, and the NRCS) and the Iowa DNR expect vegetative treatment systems to be one of the lower cost, effective runoff control options that Iowa feed-lots can use to reduce beef feedlot runoff impacts on water quality. Improved understanding of the transport and fate of nitrogen and phosphorus within and from vegetative treatment systems is necessary to improve system design and to understand long term effectiveness of the treatment system. Currently, the Iowa State University – Vegetative Treatment Area model used to design and evaluate vegetative treatment system performance is based on runoff control system hydrology. Likewise, system performance has been evaluated based on effluent flow into and out of the treatment system. To improve the design capability of the Iowa State University – Vegetative Treatment Area model and performance of these runoff control systems, nutrient transport and fate needs to be considered. The objective of this proposal is to investigate the dynamics and transport of phosphorus and nitrogen applied to the vegetative treatment area. We propose to: • Measure phosphorus sorption isotherms on soils obtained from four vegetative treatment systems in Iowa • Determine nitrogen mineralization rates for feedlot runoff • Develop phosphorus budgets for four vegetative treatment systems in Iowa • Develop preliminary nitrogen budgets for four vegetative treatment systems in Iowa The deliverables produced as a result of this study will include: • Design guidance for sizing a vegetative treatment systems based on phosphorus loading • Design guidance for sizing a vegetative treatment systems based on nitrogen loading This data will be in direct support of the Iowa Small Feedlot Teams efforts to develop runoff control strategies for open beef feedlots. Data from this study will be used to develop guidance documents for appropriate VTS sizing and ultimately to add nitrogen and phosphorus simulation capabilities to the Iowa State University – Vegetative Treatment Area model. Developing these tools will provide consultants, NRCS, the Iowa DNR, and the Iowa Small Feedlot Team with the tools necessary to install more effective runoff control systems on open feedlots, protecting the waters of Iowa. The results of this study will be used as preliminary data to seek additional funding from the USDA – Agriculture and Food Research Initiative Competitive Grants Program to further evaluate the fate and transformations of nitrogen and phosphorus occurring in these systems. Future research topics that we will seek additional funding from USDA to investigate include; quantification of nitrogen leaching from the treatment area, measurement of gaseous nitrogen emissions from the treatment system, and measurement of the mineralization of organic phosphorus.