CH4 emissions from a double-cropping rice field in subtropical China over seven years

Rice paddies are important sources of the greenhouse gas methane (CH4). However, it is difficult to precisely quantify CH4 emissions using the static chamber method because of their discontinuous measurements as well as the spatial and temporal variability of CH4 emissions. To precisely quantify CH4 emissions from rice paddies and gain deep insight into the emission rhythm and environmental effects, a seven-yearlong CH4 flux measurement was carried out continuously using the eddy covariance method in a double cropping rice paddy in subtropical China. The annual CH4 emissions were 42 & PLUSMN; 2 g C m- 2. The half hourly CH4 flux was highly correlated with gross primary production (GPP) and environmental factors, such as soil temperature (Ts), and latent heat flux (LE), which explain 47-91% of the CH4 diurnal variation. However, the peak of CH4 generally appeared at dusk during the vigorous growth period, which was quite different from the GPP peak around noon. CH4 flux seasonal dynamic were more complex, with double peaks during the growing season and lower values during the fallow season. Interestingly, in contrast to previous studies of linear or exponential relationships with short-term datasets, daily CH4 and GPP showed a logarithmic relationship at the vegetative stage in this study with seven-year data, this is crucial in improving the model accuracy in estimating annual CH4 emissions. The result implies that long-term observation is necessary to accurately assess CH4 emissions from rice paddy.