Journal Article

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

Cerri, Carlos Eduardo P., Carvalho, João Luis Nunes, Angnes, Graciele, Cherubin, Maurício Roberto

2025

Overview

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. Our findings show that the average EF for mineral fertilizers is lower than the IPCC defaults, with variation depending on crop and fertilizer type, highlighting the need for Tier 2 methodologies using region‐specific data to improve greenhouse gas inventories. Although this study is a key step in refining N2O estimates, data gaps remain in several regions, underscoring the need for further research and long‐term monitoring.

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Accuracy / Agricultural management / Alternative energy sources / Animal wastes / Assessments / Bibliometrics / Biodiesel fuels / Biofuels / Carbon footprint / Climate change / Corn / Crops / Dissertations & theses / Ecosystems / Emission / Emission inventories / Emissions / Estimates / Ethanol / Fertilizers / Fossil fuels / global climate change / Global warming / Greenhouse gas emissions / Greenhouse gases / Intergovernmental Panel on Climate Change / IPCC / Life cycle analysis / Literature reviews / Measurement techniques / Nitrogen / nitrogen fertilizer / Nitrous oxide / Organic fertilizers / Pig manure / Slurries / Subtropical zones / Sugarcane / Systematic review / Tropical environments / Uncertainty