Factors controlling diel patterns of methane emission via rice

Methane emissions from flooded rice grown under greenhouse conditions were monitored using a closed chamber technique. The three rice cultivars showed similar diel emission patterns though the amplitudes differed. Variation in emissions (maximum emission rate) from the different cultivars ranged from 0.164–0.241 mg/pot/h at tillering stage, 0.714–2.334 mg/pot/h at heading stage, 0.399–1.393 mg/pot/h at ripening stage. The methane emissions increased in the morning at accelerating rates, reached a maximum in the early afternoon, then decreased rapidly to constant rates during the night. The diel emission pattern was modeled using a Gaussian equation for daytime, and a constant for nocturnal emissions. Applying an Arrhenius equation, more than 90% of the diel variation of methane emissions could be predicted from soil temperature fluctuations. The predictions improved by using a diffusion model based on soil temperature and dissolved methane concentrations in soil solution. Soil temperature and methane concentration in soil solution are the two major factors controlling diel methane emissions.