Effect of drainage in the fallow season on reduction of CH4 production and emission from permanently flooded rice fields

Field and incubation experiments were conducted during 2007-2009 to study the effect of drainage in the fallow season on CH4 production and emission from permanently flooded rice fields. It was found that drainage in the fallow season significantly affected the temporal variations of CH4 production and emission from permanently flooded rice fields. CH4 production and emission from permanently flooded rice fields (Treatment FF) mainly occurred during the rice season, where they were found to be much lower in the late fallow season. No CH4 flux was detected from drained fields (Treatment DF) in the fallow season. Compared with Treatment FF, Treatment DF was delayed not only its onset of CH4 production and emission, but also appearance of the highest peak of CH4 production during the rice season. A significant positive relationship was observed between CH4 production rates of paddy soil and corresponding CH4 fluxes (P < 0.01). CH4 production in rice roots was the highest in rate at the rice booting stage, but was obviously lower at the rice tillering, grain filling and ripening stages, and the highest value reached at the same time as the peak of CH4 production occurred in the paddy soil. Drainage in the fallow season significantly decreased CH4 production and emission from Treatment FF. Compared with Treatment FF, Treatment DF was about 42-61% lower in mean CH4 production rate in the paddy soil during the rice season, and was reduced by approximately 56% in mean CH4 production rate in rice roots. Accordingly, Treatment DF was 20.6-30.2 g CH4 m(-2), 39-52% lower than Treatment FF in total CH4 emission during the rice season, and 44-57% lower in annual total CH4 emission. Rice yield in Treatment DF tended to be 4-7% lower than that in Treatment FF.