Nitrogen Fertilizer-Induced N2o Emission Factors for Corn Ethanol Life-Cycle Analysis

In existing biofuel regulations such as the Renewable Fuel Standard, benefit of corn ethanol relative to petroleum fuels in terms of greenhouse gas emissions (GHG) is typically evaluated based on life-cycle carbon intensity. It is well recognized that N fertilizer-induced N₂O emissions from corn production contributes significantly to ethanol carbon intensity. Typically, N₂O emissions from N fertilizers applied are calculated by multiplying N rate with a N₂O emission factor, which could be measured via field experiment or derived from a meta-analytic approach of published literature. Recently, there is a growing interest to capture spatial variations in N₂O emissions and to understand management and environmental drivers.

The objectives of this study are to (1) update fertilizer-induced N₂O emission factors using latest studies and (2) to assess impacts of spatial variability in emission factors on carbon intensity of corn ethanol. Existing N₂O emission database used in GREET life-cycle model was built in 2012 and since, about 280 new papers on this topic were published according to Web of Science. We expand existing database through a meta-analysis of published literature regarding N₂O emissions from corn-based farming systems in US. Literature review covers US-based studies published between 1990 and 2019 to update current N₂O emission factor. Fertilizer management and environmental factors will also be evaluated. Findings obtained from the meta-analysis will be used to characterize the significance of N₂O emissions in the overall GHG emissions profile of corn ethanol production in various US states.