## 3 Results and Discussion
### Inter-Seasonal Variations in CH\({}_{4}\) Fluxes and Driving Factors
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**CH\({}_{4}\) (g CH\({}_{4}\) m\({}^{-2}\))**} & \multicolumn{2}{c}{**GPP (g CO\({}_{2}\) m\({}^{-2}\))**} & \\ \cline{2-7}
**Rice Season** & **Whole** & **Before Mid-Season** & **Whole** & **Before Mid-Season** & **Mean T\({}_{\text{a}}\) (\({}^{\circ}\)C)** & **F(CH\({}_{4}\)/GPP) \%** \\  & **Season** & **Drainage** & **Season** & **Drainage** & **Drainage** & **Drainage** \\ \hline
2018 late rice & 21.63 & 13.70 & 889.53 & 242.26 & 25.83 & 2.43 \\
2019 late rice & 19.13 & 16.24 & 1245.95 & 471.40 & 26.46 & 1.54 \\
2020 early rice & 14.52 & 6.78 & 746.57 & 134.71 & 23.11 & 1.94 \\
2020 late rice & 23.95 & 21.14 & 1081.13 & 460.60 & 24.74 & 2.22 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: CH\({}_{4}\) emissions, GPP during the whole season and before mid-season drainage, mean T\({}_{\text{a}}\), and the ratio of CH\({}_{4}\) to GPP for the whole growing season in the four growing seasons. Figure 6: Time series of (**a**) SWC, (**b**) CH\({}_{4}\) fluxes, and (**c**) T\({}_{\text{5}}\) for 24–29 August 2019.  
between 2019 and 2020 late rice were originated from the CH\({}_{4}\) emissions from 24 July to 27 August. Figure 7 shows that the total precipitation and times of rainfall events greater than 10 mm from 24 July to 27 August in 2019 were clearly greater than those in 2020. As shown in Figure 5, CH\({}_{4}\) emissions of late rice in 2019 dropped sharply after mid-season drainage and remained low thereafter. Therefore, it is assumed that the drier soil conditions in the vegetative stage contributed to the lower CH\({}_{4}\) emissions in late rice in 2019. The mean T\({}_{\text{a}}\) of early rice was slightly lower than that of late rice, while the GPP was significantly lower. In addition, the total precipitation during the 2018-2020 late rice seasons and the 2020 early rice season was 415.0, 201.6, 409.8 and 1265.2 mm, respectively. It is speculated that photosynthesis decreased because of the lower temperatures and frequent rainfall events, which would have resulted in a decrease in methanogenic substrates. Thus, the difference between the CH\({}_{4}\) emissions of early and late rice originated from variations in the growth state of rice plants. The ratio of CH\({}_{4}\) emissions to GPP (FCH\({}_{4}\)/GPP) was proposed by [PERSON] et al. (2019) as being useful for estimating CH\({}_{4}\) emissions at the regional scale. The FCH\({}_{4}\)/GPP (%) values in 2018-2020 late rice and 2020 early rice in Nanchang were 2.52, 1.56, 1.97 and 1.94%, respectively. Simultaneous observations of CO\({}_{2}\) and CH\({}_{4}\) via EC are limited worldwide, and FCH\({}_{4}\)/GPP (%) has been observed to range from 1.3 to 2% in India ([PERSON] et al., 2019) and Japan ([PERSON] et al., 2019) and from 0.2% to 0.9% in a California rice paddy from 2009-2015 ([PERSON] et al., 2019). [PERSON] et al. (2019) suggested that FCH\({}_{4}\) could be estimated as a variable fraction of GPP that increases linearly with increasing T\({}_{\text{S}}\), which may be the reason why the FCH\({}_{4}\)/GPP in Nanchang was greater than that in California. Studies have indicated that FCH\({}_{4}\)/GPP depends on the soil, fertilizer type ([PERSON] et al., 2019) and flood water management ([PERSON] et al., 2019). The mechanisms by which these factors influence FCH\({}_{4}\)/GPP are an issue that merits further research.