Whole Farm Nutrient Balance Under Different Grazing Systems: Project Overview

The amount of phosphorus (P) in surface runoff from agricultural lands is of concern because of the potential for eutrophication of Iowa’s waterways. Currently, there is limited information about the total P loads in surface runoff coming from pastureland in the Midwest. Much of the P runoff is likely associated with sediment. Because foliage limits soil disruption caused by the impact of raindrops and because forage roots hold soil particles, forages harvested at an appropriate height, through suitable grazing management, should maintain water infiltration and minimize sediment and P loss in surface runoff from pastures. Grazing management may influence utilization of P by the animal, by impacting P digestibility. The objective of this project is to quantify P flows through systems operated under different grazing management practices. Figure 1 illustrates P inputs and outputs in the grazing system