Regional N2O Emission Factors From Bioethanol Crops in Brazil: Advances and Data Gaps

The recognition of bioethanol as a key strategy for mitigating greenhouse gas (GHG) emissions is closely linked to the accuracy of N₂O emission factors (EF) used in life cycle assessments. However, previous studies have shown that the default N₂O EF values recommended by the IPCC do not accurately reflect the diverse edaphoclimatic conditions found in Brazil, leading to uncertainties in GHG inventories. Therefore, establishing regional N₂O EF is essential for improving the precision of bioethanol emission estimates. In this study, we conducted a systematic literature review compiling 293 measurements from 45 field studies across different regions of Brazil. This study focuses on sugarcane (20 studies) and corn (25 studies), which are the primary crops used for bioethanol production in Brazil. Our findings indicate that the average N₂O EF for these crops is 0.72%, lower than the value reported for the tropics and sub-tropics (1.6%). When analyzed separately, sugarcane showed an average N₂O EF of 0.65%, with higher emissions from the combined use of mineral and organic N fertilizers (0.79%) compared to mineral (0.55%) or organic fertilizers alone (0.77%). For corn, the average N₂O EF was 0.84%, with mineral N fertilizers presenting the lowest EF (0.40%), while emissions increased with the combination of mineral and organic sources (0.82%), reaching the highest levels with pig slurry application (1.72%). These variations highlight the limitations of using IPCC default values for mineral and organic N fertilizers in Brazil. Our results reinforce the need for Tier 2 methodologies incorporating region-specific data to enhance GHG inventory accuracy and support targeted mitigation strategies. Although Brazil's latitudinal range spans tropical and subtropical zones, regional stratification was not applied due to the limited number of studies within each climate category, especially when further disaggregated by crop type and N fertilizer source. Despite covering key crops, fertilizer types, and multiple biomes, the current dataset still lacks representation for important agricultural regions such as Brazil's midwest, north, and northeast regions. This study represents a significant step toward refining N₂O EF estimates for bioethanol crops, contributing to more precise assessments of the sector's climate impact. However, further research is needed to cover underrepresented areas, understand long-term field dynamics, and evaluate other crop systems and management practices. Future studies should also incorporate modeling tools and real-time monitoring to reduce uncertainties and support the development of Tier 3 estimates.