Characterization of methane emissions from rice fields in Asia. III. Mitigation options and future research needs

Methane (CH4) emissions from rice fields were determined using automated me asurement systems in China, India, Indonesia, Thailand, and the Philippines . Mitigation options were assessed separately for different baseline practi ces of irrigated rice, rainfed, and deepwater rice. Irrigated rice is the l argest source of CH4 and also offers the most options to modify crop manage ment for reducing these emissions. Optimizing irrigation patterns by additi onal drainage periods in the field or an early timing of midseason drainage accounted for 7-80% of CH4 emissions of the respective baseline practice. In baseline practices with high organic amendments, use of compost (58-63%) , biogas residues (10-16%), and direct wet seeding (16-22%) should be consi dered mitigation options. In baseline practices using prilled urea as sole N source, use of ammonium sulfate could reduce CH4 emission by 10-67%. In a ll rice ecosystems, CH4 emissions can be reduced by fallow incorporation (1 1%) and mulching (11%) of rice straw as well as addition of phosphogypsum ( 9-73%). However, in rainfed and deepwater rice, mitigation options are very limited in both number and potential gains. The assessment of these crop m anagement options includes their total factor productivity and possible adv erse effects. Due to higher nitrous oxide (N2O) emissions, changes in water regime are only recommended for rice systems with high baseline emissions of CH4. Key objectives of future research are identifying and characterizin g high-emitting rice systems, developing site-specific technology packages, ascertaining synergies with productivity, and accounting for N2O emissions .