Greenhouse Gas Emissions from Agricultural Soils: Sources and Mitigation Potential

The anthropogenic emission of greenhouse gases (GHGs), that is, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), is bringing about major changes to the global environment. Whereas most of the emissions come from combustion of fossil fuels and industrial processes, agriculture accounts for 10%-12% of the total anthropogenic emission of GHGs. Emissions from agriculture amount to 5.1-6.1 Gt CO2-eq/year, including 3.3 Gt CO2-eq/year as CH4 and 2.8 Gt CO2-eq as N2O. Of the total non-CO2 emissions from agriculture, N2O emissions from soils and CH4 emissions from enteric fermentation comprise 38% and 32%, respectively. Biomass burning, rice agriculture, and manure management account for 12%, 11%, and 7% of the emissions, respectively. Compared with 1990, agricultural emissions of CH4 and N2O have increased by nearly 17%, representing a mean emissions increase of about 60 Mt CO2-eq/year. The adoption of improved management practices and mitigation technologies could help in reducing emissions. The strategies for lowering CO2 emissions include reducing the global energy use, developing low-or no-carbon fuel, and sequestering CO2 through natural and engineering techniques. Because engineering techniques are still in developmental stages, C sequestration in soil and vegetation is considered a viable option. Management practices that increase carbon input to the soil or reduce C loss, or both, lead to net carbon sequestration in soils. Appropriate water and nutrient management, cultural practices, and choice of crop cultivars can help reduce CH4 emissions from rice fields. Practices that improve N-use efficiency can reduce N2O emissions and indirectly reduce GHG emissions from N fertilizer manufacture. The global technical GHG mitigation potential from agriculture by 2030 is estimated to be 5.5-6.0 Gt CO2-eq/year. Realizing this potential will require the adoption of best available management practices with reference to soil type and LU system.