Result for: Crops: Corn for grain Soybeans
4R Practices: Source Rate Time Place

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

Dr. Matthew Helmers

Lead Researcher:

Dr. Matthew Helmers

Director, Iowa Nutrient Research Center and Dean's Professorship in the College of Agriculture and Life Sciences

Iowa State University

Start Date: 2014

End Date: 2017

Collaborating scientists and universities

  • Dr. John Sawyer, Iowa State University
  • Mr. Carl Peterson, Iowa State University
  • Mr. Chad Huffman, Iowa State University
  • Mr. Terry Tuttle, Iowa State University

Matching Funds

  • The Northwest Research Farm Association

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.

Project Goals:

  • Determine the effects of N fertilizer application and N fertilizer application timing on nitrate-N leaching losses along with potential impacts on crop yield.

  • Determine the effects of N fertilizer application and N fertilizer application timing on crop yield.

  • Disseminate project findings through peer-reviewed journal articles, Extension fact sheets, Extension presentations, and other outlets as appropriate; and provide needed scientific information for on-going review and adjustment of the Nutrient Reduction Strategy Science Assessment.

Project Results:

  • Annual variability in precipitation and drainage losses greatly affects nitrogen loads removed from corn and soybean fields.

  • Nitrogen surplus (N inputs minus N outputs) relates to drainage nitrate concentration, but the effect of flow impairs the relationship between nitrogen surplus and nitrate loading from tile drainage.

  • Hydrology of crop land soils and nutrient management need to be considered for a comprehensive assessment of potential nitrogen loss from corn and soybean rotations.

Annual Reports