Methane and nitrous oxide emissions from Indian rice paddies, agricultural soils and crop residue burning

Agricultural soils contribute toward the emission of methane (CH4) and nitrous oxide (N2O), the two important greenhouse gases (GHGs) causing global warming. A state-wise inventory of CH4 and N2O emissions from agricultural soils of India was prepared for the base year 2007 using the Intergovernmental Panel on Climate Change (IPCC) national inventory preparation guidelines. For CH4 inventory, state-specific emission coefficients were used for rice grown under upland, rain-fed, irrigated, and deepwater, the four major rice ecosystems of the country. In case of N2O, both direct and indirect emissions from agricultural soils in different states were calculated using indigenous country specific emission factors. The change in annual emission of CH4 and N2O during the period 1980 to 2007 was estimated using the same emission coefficients. Indian rice fields covering an area of 43.86 million ha under the different rice ecosystems emitted 3.37 million tons of CH4 (84.25 Tg CO2 equivalents) in 2007. The annual direct and indirect N2O-N emissions from Indian agricultural soils was estimated to be 118.67 Gg (55.5 Tg CO2 equivalent) and 19.48 Gg (9.1 Tg CO2 equivalent), respectively. The global warming potential of the agricultural soils was estimated to be 148 Tg for the year 2007. Emissions from field burning of agricultural residues resulted in an annual emission of 250 Gg of CH4 (6.2 Tg CO2 equivalent) and 6.5 Gg of N2O (1.9 Tg CO2 equivalent). Emission of CH4 from Indian rice fields has remained almost constant during this period whereas there has been an increase of 176% in N2O emissions from agricultural soils due to increased inorganic fertilizer application, however the greenhouse gas emission intensity has declined over the years due to increase in food production.