Legacy N₂O Emissions Overlooked and Crop-Specific Mitigation Solutions

Area of Science:

• Agricultural Science
• Environmental Science
• Climate Science

Background:

• Nitrous oxide (N₂O) emissions from agricultural soils are a major concern, primarily from nitrogen fertilizer use.
• Current IPCC guidelines may underestimate N₂O emissions by not fully accounting for legacy effects of nitrogen fertilization.
• Significant variance in N₂O estimates necessitates a more comprehensive approach to emission factors.

Purpose of the Study:

• To map crop-specific legacy N₂O emission factors (EF_L) for wheat, maize, and rice using global long-term field data.
• To quantify the contribution of legacy N₂O emissions to overall agricultural emissions from staple crops.
• To update the IPCC emission factor methodology and inform mitigation strategies for climate-resilient agriculture.

Main Methods:

• Synthesized global long-term field data (≥3 years) on N₂O emissions from wheat, maize, and rice.
• Calculated crop-specific legacy N₂O emission factors (EF_L) considering management and environmental conditions.
• Compared total N₂O emissions (direct + legacy + background) with IPCC Tier 1 estimates.

Main Results:

• The global mean EF_L was 0.09% for wheat, 0.17% for maize, and 0.04% for rice.
• Legacy N₂O emissions from global wheat, maize, and rice were 0.02, 0.04, and 0.01 Tg N₂O-N season^-1, respectively.
• Total fertilizer-induced direct and legacy N₂O emissions from these crops were ~30% higher than IPCC Tier 1 estimates, with background emissions contributing 24.8%.

Conclusions:

• Legacy N₂O emissions are a significant, often overlooked, component of agricultural greenhouse gas inventories.
• Improved nitrogen management practices in staple crop production can substantially reduce N₂O emissions.
• Mitigation strategies offer potential for significant reductions in N₂O emissions, increased crop yields, and enhanced food security.