4R N Management Science Consensus to Modify Nitrous Oxide Estimation in the Field to Market Fieldprint Calculator

Many leaders of the global food supply chain are members of the large Field to Market Alliance for Sustainable Agriculture (>100 members). Several have committed to sizably reduce emissions of greenhouse gases (GHGs) (e.g., Pepsico - 25% by 2015; Walmart 20 MMT reduction by end of 2015; Unilever carbon positive by 2030; Monsanto - cumulative reduction of 45% from 2002; Kellogg’s – 65% by 2050), and recognize that nitrogen (N) inputs often account for the largest portion of cropping system GHG emissions. Several companies and environmental non-governmental organizations have incorrectly thought U.S. farmers (esp. corn farmers) universally apply 20 to 30% more N than needed for optimal yields; though in 2012, the USDA Economic Research Service and IPNI reported that corn farmers steadily improved their use since 2000. By 2010, 65 to 70% of U.S. corn farmers applied N at rates at or below university research-based N recommendations; and on average, those who rotated with soybeans used rates quite close to the university recommendations. Field to Market’s Fieldprint Calculator uses a constant factor to estimate both direct and indirect emissions of nitrous oxide (N₂O: potent GHG with ~300x warming effect compared to carbon dioxide) using a single coefficient from the Intergovernmental Panel on Climate Change (IPCC). These factors caused many food supply chain members to ask farmers to reduce fertilizer N use, for reduced N₂O emissions.

Project leaders assembled scientists to develop suites of 4R N management practices that are critically important for GHG emission reduction; and that N₂O emissions are sensitive to land resource regions in the U.S. (including cropping systems and soil texture). A new method of N₂O emission estimation was proposed for U.S. corn, soybean, and wheat systems. The new estimation method is being piloted by Field to Market in 2017 offers advantages because it:

· is consistent with current USDA GHG modeling that is sensitive to different land resource regions, surface soil texture, and crop;
· is sensitive to the actual applied N inputs by farmers (not just historic rates); and
· allows for downward adjustments of N₂O emissions (7 to 14%) if farmers use N science-consensus-developed suites of N management practices that represent Intermediate or Advanced/Emerging 4R practice implementation.

An Issue Review was published in 2016 (http://www.ipni.net/issuereview) on the suites of 4R N management practices; which are also important to improved crop yields, water quality, and soil health.