Managing Non-Growing Season Runoff Phosphorus Losses in Iowa with Grass Filter Strips and Soil Amendments.

Phosphorus losses with surface runoff are greater and more likely during periods with high probability of high-intensity rainfall and when annual crops biomass is not present or limited, especially with little residue cover. For Iowa climate and corn (Zea mays L.) and soybean (Glycine max L. Merr.)  rotation systems, the most critical period for P losses with surface runoff is from March until late June. During this period there is little or no crop vegetation and runoff from late-winter snowmelt and high-intensity spring rainfall occurs. The presentation will share results of recent research to evaluate the impacts of prairie filter strips of different sizes and design as well as amendments on loss of dissolved and particulate P with surface runoff. For the field scale prairie strips study, the treatments were (1) 100% row-crop, (2) 90% row-crop with 10% prairie at the bottom of the watershed, (3) 90% row-crop with 10% prairie integrated along strips, and (4) 80% row-crop with 20% prairie integrated along strips. For the amendments study, a field rainfall simulation technique was used to assess the value of alum and gypsum additions when manure from egg layers was applied.