METHANE PRODUCTION AND ITS FATE IN PADDY FIELDS .5. FATE OF METHANE REMAINING IN PADDY SOIL AT HARVESTING STAGE

The fate of CH4 in paddy soil at the harvesting stage was studied in pot experiments. The amount of CH4 retained in soil at the harvesting stage before drainage corresponded to 4-6% of the total amount of CH4 emitted to the atmosphere throughout the growth period. Almost all of the CH4 in soil was released to the atmosphere within 3 d after drainage in the rice-planted treatments, while CH4 was hardly released in the fallow pot without development of cracks. When cracks developed, an amount of CH4 2.8 times as large as that emitted throughout the growth period was released in the fallow pot. Harvesting without drainage, which was considered to accelerate the senescence of roots, did not influence the CH4 emission rates. The small increase of CH4 emission rates by transferring pots into the phytotron (daytime: 30-degrees-C, night time: 25-degrees-C) from the open air (14-25-degrees-C) indicated that the temperature was not the major factor for the low CH4 emission rates at the harvesting stage before drainage.