Impacts of 4R Nitrogen Management on Crop Production and Nitrate-Nitrogen Loss in Tile Drainage

Project Summary

Corn and soybean producers in Iowa and throughout much of the U.S. Corn Belt are increasingly challenged to maximize crop production to supply feed, fiber, and more recently biofuels (especially ethanol from corn) while at the same time managing soils by utilizing fertilizers and animal manures efficiently and minimizing negative impacts on water quality. In particular, there is concern about nutrient export from subsurface drainage and surface water runoff to water systems in Iowa and the Gulf of Mexico. In addition to local impacts on receiving waters, nitrogen (N) and phosphorous (P) loads from U.S. Corn Belt are suspected as primary drivers of hypoxia in the Gulf of Mexico. The EPA SAB’s 2007 hypoxia reassessment identified both N and P as major contributors to Gulf hypoxia and the 2008 Action Plan called for a dual nutrient strategy of 45% reductions in both N and P loads. Relative to N loss, nitrate‐N is the predominant form in many agricultural watersheds due to subsurface drainage or shallow subsurface flow. Nitrate‐N loading from the Mississippi River is suspected to be a main contributor to the hypoxic zone in the Gulf of Mexico, and the main source of nitrate‐N in the Mississippi River Basin has been linked to subsurface drainage in the Midwest. Based on the need for nitrate‐N reductions to meet water quality goals, new management practices are needed that have the potential to significantly reduce nitrate‐N losses at minimal cost and/or provide economic benefits. Practices are needed that will address the right source at the right rate in the right place. In addition, there is a need to quantify the water quality and crop yield impacts of some traditionally recommended best nutrient management practices such as timing of N application The Iowa Nutrient Reduction Strategy Science Assessment has indicated nitrate‐N loss improvement with certain practices, such as time of application (spring versus fall) and nitrification inhibitor. However, the published data available for the science assessment was limited for those practices, especially from Iowa research. Also, the practice of split or in‐season application had indication of limited benefit to tile drainage nitrate‐N reduction. Among other practices, the Iowa Nutrient Reduction Strategy specifically identified in‐season sensor‐based nitrogen application and nitrogen inhibitors needing of future research that would concurrently document crop production and water quality (nitrate‐N loss) effects.