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 significant concern, primarily from nitrogen fertilizer. The IPCC methodology, while providing default emission factors (EF_D), overlooks postseasonal N₂O emissions from legacy nitrogen fertilization effects.
• This oversight leads to substantial variance in N₂O estimates, particularly for staple crops like wheat, maize, and rice, impacting climate change assessments and mitigation strategies.

Purpose of the Study:

• To synthesize global long-term field data to map crop-specific legacy N₂O emission factors (EF_L) for wheat, maize, and rice.
• To provide a more accurate accounting of total fertilizer-induced N₂O emissions, including both direct and legacy components.
• To identify crop-specific mitigation strategies for reducing N₂O emissions and enhancing agricultural sustainability.

Main Methods:

• Global synthesis of long-term (≥3 years) field data on N₂O emissions from wheat, maize, and rice cultivation.
• Calculation of crop-specific legacy N₂O emission factors (EF_L) that integrate management and environmental conditions.
• Comparison of synthesized emission estimates with current IPCC Tier 1 methodology.

Main Results:

• The global mean legacy N₂O emission factors (EF_L) were determined as 0.09% for wheat, 0.17% for maize, and 0.04% for rice.
• Legacy N₂O emissions from global wheat, maize, and rice were estimated at 0.02, 0.04, and 0.01 Tg N₂O-N season^-1, respectively, constituting 7.3%, 12.6%, and 5.6% of N fertilizer-induced emissions.
• Total direct and legacy N₂O emissions from these staple crops were ~30% higher than IPCC Tier 1 estimates, with background emissions contributing 24.8%.

Conclusions:

• The study provides updated, crop-specific legacy N₂O emission factors, improving the accuracy of global N₂O accounting from staple crops beyond current IPCC guidelines.
• Implementing crop-specific nitrogen management strategies can significantly reduce global N₂O emissions (by 0.47 Mt), increase crop production (by 362.8 Mt), and support global food security.
• Findings offer critical insights for developing climate-resilient agricultural practices and refining climate change mitigation policies.