Simultaneous measurements of CH4 emission,CH4 production and transport through rice plant,gas bubble and diffusion in flooded water show that:low oxidation occurs in the afternoon when CH4 transport efficiency appears higher. CH4 emission rate is lower in cloudy and raining weather when the CH4 oxidation rate in the paddy soil higher. Higher transport efficiency appears in early and middle June for the early rice,while for the late rice,it is in late July shortly after rice is transplanted. This difference is mainly caused by different weather trend in the individual rice growing period. Because the relative importance of methane oxidation is not the same in the whole rice growing period,the seasonal variation of CH4 production rate in the paddy soil can not explain that of CH4 emission. Better correlation between the two parameters may happen only in a short time period when rice growing status and weather condition remain relatively stable.
Obvious concentration gradient is observed in the internal space of rice plant. Higher CH4 emission rates have been measured in the weeds-growing field than in unplanted field , and the former is very similar to that of rice-planted field. The seasonal variation in non-rice-planted field is different from that in rice planted field,with no peak before harvesting. Experiments show that the portion emitted through rice plant is changing during the growing season. For early and late rice,methane emitted through rice plant accounts in average for 73. 18% (43. 07-97. 88%) and 54. 98% (11. 00 - 99. 95%) of the total flux re- spectively. The above result shows that the role of rice plant in methane emission is greater for early rice. The seasonal variation of transport ability of rice plant appears similar for early and late rice, which increases with the time and reaches maximum at mid-heading stage,then decreases with rice riping. The CH4 transport ability of rice correlates well linearly with the plant height. CH4 concentration in soil pore water is much higher than tha
Advances in Earth Sciences
methane,transport,rice plant,rice field.