Methane and nitrous oxide emission from irrigated rice fields: Proposed mitigation strategies

Rice fields are major sources of CH4 and N2O. A number of practices have been suggested to minimize the emission of either of these gases, but simultaneous mitigation of these gases are not widely discussed. Mitigating CH4 emission may increase N2O emissions and vice versa. Reducing their emission and making the cumulative radiative forcing a minimum is a priority. The strategies should be effective, applicable on a large scale, technically feasible, economic, less time-consuming, environment friendly and should be easily acceptable. On the basis-of the available literature on CH4 and N2O mitigation, the following measures are suggested by the author to mitigate the emissions of these two gases simultaneously from irrigated rice fields: (1) Application of mid-season drainage which does not coincide with high ammonium in soil, (2) application of urea and NH4+-based fertilizers in 4 splits with nitrification inhibitors to increase N use efficiency, (3) replacement of ammonium sulphate with other sulphate sources to minimize CH4 and N2O emissions, (4) replacement of N broadcasting by foliar-N spray application, (5) sub-surface application of urea supergranules, (6) incorporation or deep placement of prilled urea instead of surface application, (7) application of well-composted organic matter in place of fresh organic matter and green manure, (8) use of single superphosphate (SSP) basally, which in addition to supplying phosphorus, could mitigate CH4 production by supplying sulphur to soil and (9) cultivation of rice varieties with low gas transport capacities and low exudate formation. These practices can be taken up without much difficulty in irrigated rice fields and can reduce CH4 and N2O emission simultaneously.