FACTORS AFFECTING METHANE EMISSION FROM RICE FIELDS

Emission of CH4 from ricefields is the result of anoxic bacterial meth ane production. Global estimates of annual CH4 emission from ricefield s 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 nega te gains in rice production and productivity. Field studies at the Int ernational Rice Research Institute show that soil and added organic ma tter 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. T he production and transport of CH4 to the atmosphere depend on propert ies of the rice plant. Under the same spacing and fertilization, the t raditional variety Dular emitted more CH4 per day than did the new pla nt type IR65597. Upon flooding for land preparation anaerobic conditio ns result in significant amount of methane being formed. Drying the fi eld at midtillering significantly reduced total CH4 emissions. Large a mounts of entrapped CH4 escape to the atmosphere when floodwater reced es upon drying at harvest. Cultural practices may account for 20% of t he overall seasonal CH4 emissions.