牲畜和水稻系统中的甲烷排放——来源、量化、缓解和指标（英）-352页_3mb

Summary of Methane Emissions in Livestock and Rice Systems

Core Content

This document, published by the Food and Agriculture Organization (FAO) in 2023, provides a comprehensive overview of methane emissions from livestock and rice systems, including their sources, quantification methods, mitigation strategies, and metrics for assessing their climate impact. It serves as a reference for policymakers, stakeholders, and researchers aiming to reduce greenhouse gas (GHG) emissions in the agrifood sector.

Main Sources of Methane Emissions

• Ruminant livestock are the primary source of methane emissions, particularly through enteric fermentation.
• Manure contributes significantly to methane emissions, especially during storage and application.
• Soil acts as both a source and a sink for methane, influenced by microbial activity and land management practices.
• Anaerobic digestion is a process that can produce methane, but also has potential for mitigation through leakage reduction.

Methane Sinks

• Soil can absorb methane, but this capacity is affected by various factors such as soil type, moisture, temperature, and microbial activity.
• Land management practices can enhance or reduce the soil's ability to act as a methane sink.

Quantification of Methane Emissions

• Measurement techniques include:
  • Animal-based methods: Gas exchange, tracer, open-path laser, and in vitro techniques.
  • Facility-based methods: Manure storages and soil flux measurements.
  • Large-scale methods: Aircraft and satellite/drone imagery.
• Estimation approaches are:
  • Bottom-up: Models based on detailed data on animal and manure management.
  • Top-down: Comparative analysis with bottom-up data to validate emission estimates.
• Uncertainties in quantification are acknowledged, emphasizing the need for improved methodologies and data.

Mitigation Strategies

Livestock-related Mitigation

• Animal breeding and management:
  • Increased production can reduce methane per unit of product.
  • Selection for low methane-producing animals is a promising strategy with moderate efficacy.
  • Improved feed efficiency reduces methane emissions by optimizing nutrient use.
  • Improved animal health can lower emissions through better productivity and reduced stress.
  • Improved reproduction enhances productivity and reduces emissions.
• Feed management:
  • Increased feeding levels improve efficiency and reduce methane per unit of output.
  • Decreased forage to concentrate ratio lowers methane emissions by altering microbial activity.
  • Starch concentrate sources and processing influence methane production.
  • Supplementation with lipids can reduce methane emissions.
  • Other seaweeds and tannin extracts show potential for methane suppression.
  • Saponins and biochar are explored as mitigation tools.
  • Direct-fed microbials and early life interventions are considered for their impact on rumen microbiota.
  • Phage and lytic enzymes offer a novel approach to targeting methanogens.

Manure and Land Application

• Biogas collection and utilization is an effective way to capture methane and convert it into energy.
• Decreased manure storage temperature reduces methane emissions.
• Manure acidification through dietary or direct amendment can suppress methanogenic activity.
• Methane inhibitors are chemical compounds that reduce emissions from manure.
• Decreased storage interval minimizes methane release.
• Solid-liquid separation and composting/aeration improve manure management and reduce emissions.
• Biofilters and scrubbers help in capturing methane from manure systems.
• Manure incorporation and injection can reduce emissions by altering soil conditions.
• Application timing of manure affects methane release.

Rice Paddy Methane Emissions

• Water management is a key strategy to reduce methane emissions from rice paddies.
• Organic amendments and fertilizer use influence methane production.
• Planting methods and crop management can decrease emissions.
• Rice variety selection plays a role in reducing methane output.
• Straw burning reduction is essential for mitigating emissions.
• Emerging technologies offer new possibilities for methane abatement in rice systems.

Cross-cutting Mitigation

• Integrated approach is encouraged for methane mitigation, considering the entire production chain.
• Life cycle assessment (LCA) and carbon footprinting are used to evaluate the climate impact of different systems.
• Cost-benefit and cost-effectiveness analyses help in choosing the most viable mitigation options.
• Policy frameworks are suggested to support methane reduction in agriculture.

Metrics for Methane Impact

• Global Warming Potential (GWP) and Global Temperature Potential (GTP) are used to quantify methane's climate impact.
• Pulse-emission metrics and step-pulse metrics are discussed for their differences in assessing short-term and long-term climate effects.
• Time horizon and discount rates are important considerations in metric selection.
• Non-radiative forcing impacts are also evaluated, such as effects on air quality and health.
• A metric selection guide is provided, outlining key features and limitations of various metrics.

Conclusion

The report highlights the importance of methane mitigation in achieving climate goals, particularly under the Global Methane Pledge, and supports the FAO's strategy on climate change. It emphasizes the need for scientific research, policy integration, and innovative solutions to reduce emissions from livestock and rice systems. The LEAP Partnership has played a critical role in analyzing and summarizing the data, offering a robust basis for future actions.