Long-Term Carbon Dioxide Flux in Flooded and Non-Flooded Rice Paddy Fields in Temperate and Tropical Regions.

It is thought that increases in greenhouse gases greatly influence a global climate change. Carbon dioxide (CO₂) is a major greenhouse gas resulted from human activities.  A great amount of greenhouse gases is emitted from agricultural fields. Rice is grown in paddy fields in Asian regions, and their areas account roughly 90 % of the total world rice paddies fields. Because various climatic zones existed in the Asian regions, climatic condition, soil environment and cultivation management are different. Carbon dioxide emission is supposed to be affected. Study sites for temperate and tropical regions were selected at paddy fields in Japan and Thailand, respectively. Study periods were between May and November 2015 in Japan, and between June and December 2014 in Thailand. We evaluated CO₂ flux in rice paddy fields using the eddy covariance method. Carbon dioxide flux showed positive values, meaning emission, from transplant to DAT (day after transplant)=20 at the two sites and showed negative values, meaning absorption, afterward. At the both two sites CO₂ absorption rates reached the maximum at the end of reproductive stage (in Japan approximately DAT=70, and in Thailand approximately DAT=80). At the rice paddy field in Japan showed CO₂ emission at around DAT=50 because the field was temporarily drained in the middle of the growing season. At the both sites CO₂ absorption decreased at the end of a reproductive stage and CO₂ emission started again at DAT=100 in Japan, and just before harvest in Thailand. At the both sites where the fields were drained after harvest CO₂ emission was observed.