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Methane emissions from rice fields in China were measured at eight sites in five provinces under conditions representative of local practices for rice cultivation. Methane emission rates during the rice growth period varied greatly from site to site and with treatments at the same site, ranging from 0.3 to 205 g CH 4 /m 2 . Flooded or waterlogged rice fields in the nonrice growth season continuously emitted CH 4 substantially. The average CH 4 emission rate from a rice field in Chongqing was as high as 36.2 g CH 4 /m 2 in the nonrice growing season. Furthermore, flooding in the nonrice growth season also significantly stimulated CH 4 emission during the rice growth period in the next year. Increases in the rate of CH 4 flux after rice transplanting were less when the number of consecutive upland crops grown before rice transplanting was greater. CH 4 emissions from rice fields located on downslope was larger than from those on midslope and upslope in hilly areas due to poor drainage of the former. Application of rice straw in fall when winter wheat was sown did not increase CH 4 emission significantly during the following rice growth period. CH 4 emission was depressed by the application of ammonium sulfate but was, in general, not significantly affected by urea application.
Cai et al. (Sat,) studied this question.