Factors affecting methane emission from rice fields

Emission of CH4 from ricefields is the result of anoxic bacterial methane production. Global estimates of annual CH4 emission from ricefields is 100 Tg. CH4 emission data from limited sites are tentative. It is essential that uncertainty in individual sources is reduced in order to develop feasible and effective mitigation options which do not negate gains in rice production and productivity. Field studies at the International Rice Research Institute show that soil and added organic matter are the sources for initial methane production. Addition of rice straw enhances methane production. Roots and root exudates of wetland rice plants appear to be the major carbon sources at ripening stage. The production and transport of CH4 to the atmosphere depend on properties of the rice plant. Under the same spacing and fertilization, the traditional variety Dular emitted more CH4 per day than did the new plant type IR65597. Upon flooding for land preparation anaerobic conditions result in significant amount of methane being formed. Drying the field at midtillering significantly reduced total CH4 emissions. Large amounts of entrapped CH4 escape to the atmosphere when floodwater recedes upon drying at harvest. Cultural practices may account for 20% of the overall seasonal CH4 emissions.