Agriculture’s Greenhouse Gas Challenge: A Growing Climate Concern
In 2021, agrifood emissions reached 16 Gt CO2e, representing 30% of total human emissions. Farm operations account for 48% of these emissions, with pre/post-production at 33% and land-use change at 19%.
While working to reduce emissions, the sector must maintain food security, soil health, biodiversity, and farmer income. Key solutions include improving crop yields through responsible crop nutrition. Yet, fertilizer use generates emissions during production, transport, and application.
Nitrogen fertilizer has the largest impact on greenhouse gas emissions. Production creates 0.44 Gt CO2e annually, while field applications generate N2O emissions through soil processes. Total nitrogen fertilizer emissions reach 1.13 Gt CO2e, with China, India, USA, and EU28 responsible for 62%.
Manure and organic fertilizers add another 1.0 Gt CO2e annually in N2O emissions. Together with mineral fertilizers, total nitrogen-related emissions reach 2.13 Gt CO2e or 4% of world’s total emissions, while other fertilizers contribute minimal emissions. Efficient nutrient use can help mitigate emissions, which is why optimizing nitrogen use efficiency and minimizing N2O emissions are particularly important.
The challenge is balancing nitrogen fertilizer use for crop production and climate impact reduction. In this Issue Brief, we examine how responsible plant nutrition can mitigate emissions through improved practices and technologies, while addressing implementation challenges and measurement issues.
Key Trends and Global Challenges in Agricultural Nitrogen Management
- Global Nitrogen Fertilizer-Related Trends
From the 1960s to 1990s, nitrogen fertilizer use and crop production increased while nutrient use efficiency in croplands declined. Recent decades saw rises in crop production and nitrogen input, with global nutrient use efficiency reaching 55% in 2021. Nitrogen surplus has stabilized at 80 million tons, with significant regional variation. Farm gate N2O emissions increased to 2.1 Gt CO2e by 2021, mainly from fertilizer use. The key challenge is reducing the nitrogen surplus and N2O emissions while improving productivity and nutrient use efficiency.
- Characteristics of Nitrous Oxide Emissions
Soil N2O emissions mainly come from microbial nitrification and denitrification processes, regulated by environmental and abiotic factors. N2O emissions increase after applying nitrogen fertilizers and heavy rainfall due to excess nitrogen and moisture. These emissions occur in concentrated ‘hot spots’ and during ‘hot moments’, making them spatially and temporally variable. Soil conditions, climate, and management practices affect emission levels, creating challenges for measuring emissions and implementing mitigation strategies.
- Interventions to Reduce N2O Emissions
Novel fertilizers and improved farming practices can reduce soil N2O emissions. While these methods combined with balanced nutrition can reduce agricultural greenhouse gas emissions, increasing soil organic carbon may boost N2O emissions, requiring careful nitrogen management.
- Interventions to Increase Yields and Nitrogen Use Efficiency
Regions with low nitrogen use have only limited potential to reduce their N2O emission. However, these areas need increased yields on existing cropland to ensure food security and prevent deforestation. Their degraded soils require mineral and organic fertilizers, plus improved agronomic practices through Integrated Soil Fertility Management.
From Farm to Policy with Effective Actions
- Recommended Implementation Actions
Success in reducing N2O emissions requires farmer buy-in and adoption of proven practices. While some ‘win-win’ practices are already adopted, others need incentives to encourage implementation. Here, we outline three action targets.
Target 1 addresses regions with excessive nitrogen rates and substantial surplus. Implementing the Right Rate principle can reduce emissions while increasing profits. Non-linear emission factor models will accurately capture emission reductions.
Target 2 focuses on regions with optimal nitrogen rates, emphasizing reduced ammonia loss through improved timing, placement, and inhibitor use. This will reduce indirect N2O emissions while rate adjustments to account for avoided ammonia loss will boost yields and profits.
Target 3 applies where yields and efficiency are already optimal. It prioritizes direct N2O emission reduction through controlled-release fertilizers and inhibitors. Since these may not increase profits, support mechanisms could be needed.
- Policies to Drive Implementation
These measures aim to improve nutrient use efficiency and reduce greenhouse gas emissions while maintaining food security. Policy changes and subsidies should incentivize cost-effective practices that balance yield, profit, and environmental impact.
While evidence for effective policies remains limited, carbon markets offer another path forward by rewarding farmers for reducing emissions. This includes reducing fertilizer application, increasing nutrient use efficiency, and using emission-reducing technologies.
Financial incentives can come through sustainability financing, with governments redirecting support and banks offering better terms for environmentally-conscious farming practices. These approaches are especially important for practices that benefit the public more than individual farmers.
Metrics to Monitor Progress
Metrics are needed to track progress on emission reduction and efficiency goals. Current sustainability metrics focus on nitrogen rates while neglecting practices like placement and inhibitors. This limited scope affects which practices qualify for incentives and may lead to undesired yield losses.
A practical alternative is estimating N2O emissions through partial crop nitrogen balance – the difference between nitrogen inputs and crop nitrogen removal. This method shows stronger correlation with emissions than nitrogen application rates alone. While easily implemented through farm software, this approach may miss short-term emission peaks and inhibitor effects.
Recent advances show that emission reduction through Responsible Plant Nutrition is feasible. Yet, it requires aligned stakeholder action and appropriate incentives to overcome adoption barriers.
Who needs to do what to reduce greenhouse gas emissions?
Governments:
- Create policies incentivizing proven nitrogen efficiency and greenhouse gas reduction practices, including inhibitors and controlled-release fertilizers
- Partner with industry on delivery programs and market-compatible emission reporting
- Update methodologies to track emission reductions in national greenhouse gas inventories
Industry:
- Implement Scope 3 emissions reduction programs with documented results
- Follow N2O emission reduction standards and participate in carbon markets
- Train crop advisers to verify emission-reducing practices
- Develop greenhouse gas mitigation technologies, including smart fertilizers and precision nitrogen management
- Support regional research on 4R practices
Carbon market participants and investors:
- Create transparent standards for carbon credits based on N2O emission reduction practices
- Develop carbon market programs that reward farmers for reducing N2O emissions through improved practices
Farmers and other practitioners:
- Apply 4R nutrient practices based on crop needs and soil conditions, using decision-support tools
- Track and document farm practices, share data for sustainability metrics and exchange knowledge with peers
Researchers:
- Study new methods to boost nitrogen use efficiency and cut emissions
- Create better tools and models for estimating emission reductions
- Assess practice effectiveness and work with farmers to identify practical solutions
