Reducing Nitrous Oxide Emissions From US Row–Crop Agriculture through Nitrogen Fertilizer Management: Development of An Nitrous Oxide Emissions Reduction Protocol.

Nitrous oxide (N₂O) is the major greenhouse gas emitted by US agriculture. About 80% of N₂O emissions emanate from N fertilizer application and other soil management activities, with cropland emissions alone greater than 1 Tg yr^-1.

Manipulating fertilizer N inputs is a readily accessible management tool for increasing crop N use efficiency, with fertilizer N rate a crucial parameter for estimating both yield and N₂O emissions in row–crop systems.

Quantification of the trade–offs between N₂O emissions, crop yield and fertilizer N rate is essential for proposing strategies which optimize productivity at economically and environmentally favorable N rates.

The relationship between fertilizer N rate and subsequent N₂O emissions is typically assumed linear and insensitive to increasing N rate. However, recent studies at the Kellogg Biological Station in SW Michigan, in winter wheat and corn, using automated chambers to monitor near–continuous N₂O emissions from a field scale, rain–fed N fertility gradient, suggest that a non–linear relationship is more applicable.

Emissions of N₂O in both crops were low at fertilizer N rates below or coincident to those optimizing crop yield, but sharply increased thereafter. This threshold response to increasing fertilizer N rate in row–crop agriculture suggests a substantial decrease in N₂O emissions could be achieved with moderate reductions in N rate and little or no yield penalty.

Our data, in conjunction with a recently developed approach for determining economically profitable N application rates for optimized crop yield in the Corn Belt states, have potential to be incorporated into agricultural N₂O emission reduction protocols and utilized in future projects suitable for inclusion in the burgeoning nutrient cap–and–trade markets.

We will present results from our 2007–2009 field seasons and outline a protocol framework for reducing  N₂O emissions from row–crop agriculture in the US Midwest.