Nitrous Oxide Emissions from the Application of Fertilizers: Source Partitioning

Meta-analysis review of the 4R impacts on nitrous oxide emissions in the Midwest U.S.

IPNI-2011-USA-CA32

02 Jan 2013

2012 Annual Interpretive Summary


One of the undesirable N loss pathways from cropland is the emission of nitrous oxide (N2O), a potent greenhouse gas and ozone depleting substance. This study explores the potential of alternative agronomic management practices to mitigate N2O emissions from corn cropping systems in major corn producing regions in the USA and Canada by synthesizing available data from peer-reviewed literature. An acceptable number of side-by-side comparisons for meta-analysis was available for manure versus synthetic fertilizer, polymer coated urea versus conventional urea fertilizer application, synthetic fertilizer with vs. without urease plus nitrification inhibitor, no-till versus tilled cropping systems, and continuous corn cropping systems vs. corn-soybean rotations. For studies that included unfertilized control N-treatments, fertilizer induced emissions (FIE) were determined as the difference in N2O emissions in fertilized and unfertilized plots, divided by the N-rate. The FIE index normalizes N2O emissions for differences in environmental characteristics and N-rate between studies. Consequently, FIE was used to assess the effects of agronomic management practices across studies, as a way to overcome the gap in data availability.

Based on currently available data, the use of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) in combination with the nitrification inhibitor dicyandiamide (DCD) was the only management strategy that consistently reduced N2O emissions. Manure application caused higher N2O emissions compared to the use of synthetic fertilizer N. This warrants further investigation in appropriate manure N management, particularly in the Lake States where up to 30% of corn cropland typically receive manure. The N2O response to increasing N-rate varied by region (USDA Land Resource Regions in the USA and Ecozones in Canada), and was either linear, exponential, or not significant. N2O emissions did not show a better fit to N-surplus, defined as the difference between N applied and grain N removed by harvest, compared to N-rate. In general, great variability around N2O emissions and a highly significant effect of region on FIE suggest that N2O emissions and appropriate mitigation strategies are best assessed on a regional as opposed to national or international level. Furthermore, more data on side-by-side comparisons of common and alternative management practices, especially those pertaining to N-placement, N-timing and N-source, will be needed to further develop and improve N2O mitigation strategies for corn cropping systems in the major corn producing regions in the USA. CA-32