Legacy N₂O Emissions Overlooked and Crop-Specific Mitigation Solutions

Agricultural soil nitrous oxide (N₂O) emissions primarily originate from three sources: nitrogen fertilizer-induced direct seasonal emissions and postseasonal legacy emissions, and soil background emissions. While the IPCC has presented the global default value of fertilizer-induced direct N₂O emission factors (EF_D), it did not account for postseasonal N₂O emissions induced by the legacy effects of historical N fertilization in staple crops, leading to significant variance in N₂O estimates in the IPCC EF methodology. Here, we synthesized global long-term field data (≥3 years) to map crop-specific legacy N₂O emission factors (EF_L), reflecting integrated system-level effects, including management and environmental conditions. The global mean value of EF_L was 0.09, 0.17, and 0.04% for wheat, maize, and rice production, respectively. Legacy N₂O emissions from global wheat, maize, and rice were estimated to be 0.02, 0.04, and 0.01 Tg N₂O-N season^-1, accounting for 7.3, 12.6, and 5.6% of N fertilizer-induced emissions, respectively. Fertilizer-induced direct and legacy N₂O emissions from three staple crops totaled 0.87 Tg N₂O-N season^-1, ∼30% higher than IPCC tier 1 estimates. Background N₂O emissions contributed 24.8% of the total emissions from staple crops. Crop-specific mitigation solutions through improving N management could reduce global N₂O emissions from three staple crops by 0.47 Mt, increase crop production by 362.8 Mt, and potentially feed an additional 8 million people by 2100. Our findings update the IPCC EF methodology for accounting fertilizer-induced direct and legacy N₂O emissions from staple crops and provide insights into mitigation strategies for climate-resilient agriculture.