## 2 Materials and Methods  
### Study Site and Crop Management  
The experiment was conducted from 2018 to 2020 on the Ganfu Plain, Jiangxi Province, China (Figure 1). The climate in the study region is characterized as subtropical, humid and monsoonal. The mean annual temperature is 18.1 \({}^{\circ}\)C, and the mean annual precipitation is 1634 mm. The soil is a paddy soil with a clay loam texture.  
The experiment was conducted at ST1 in 2018 under transplanted and mild AWD irrigation. The detail of mild AWD has been reported by [PERSON] [21]. To observe the variation in CH\({}_{4}\) flux under direct-seeded and local farms' traditional irrigation method, another experiment was conducted at ST2 in 2019-2020. Local farmers generally adopt the flooded irrigation method with mid-season drainage, which would avoid ineffective tillering. However, as reported by [PERSON] et al. [54], in 2019, Jiangxi experienced continuous drought in summer and autumn, the influence of which was the widest and strongest since meteorological records. Frequent flooded and non-flooded alternates occurred at ST2 in 2019 owing to farmers' lack of timely irrigation. Therefore, the irrigation methods for late rice in 2019 and 2020 were AWD and flooded with mid-season drainage respectively. Mid-season drainage in 2018 late rice and 2020 early rice were failed because of rainfall events during the period. Owing to frequent rainfall events and instrument malfunctions, the data from early rice in 2018 and 2019 were not qualified. As reported by [PERSON] et al. [49], during the  
Figure 1: Location of Ganfu Plain. (**a**) Sketch map of the station location; (**b**) Setup of the eddy covariance system at ST2 with a WindMaster Pro ultrasonic anemometer, LI7500A open-path CO\({}_{2}\)/H\({}_{2}\)O analyzer, and LI-7700 open-path CH\({}_{4}\) analyzer; (**c**) Google Earth map of ST1 and ST2 (the yellow circles indicate the position of the eddy covariance towers).  
rainy periods the raindrops and dirt would accumulate on the mirrors. Continuous rainfall prevented the self-cleaning system from cleaning the mirror because the cleaning fluid stored in the washer was used up in a short time, thus the signal strength of the instruments was very low (10%) during the rainy periods. Therefore, the data from early rice in 2018 and 2019 were not included in the analysis. Both sites were located in the centre of homogeneous paddy fields. Since the 2 sites were only 1.45 km away, the climate pattern, soil type, wind direction and rice cultivar were the same. However, the field management among years was different to create variability between the influencing factors, and the timing of the crop rotation at the two sites is listed in Table 1. The seeds of the rice at ST2 were broadcast at a rate of 300 seeds m\({}^{-2}\), and the late rice at ST1 was transplanted at a rate of 100 seeds m\({}^{-2}\). The total N fertilizer applied was 162 kg N hm\({}^{-2}\) for the late rice at ST1, and fertilizer was applied as basal fertilizer and at the tillering and panicle initiation stages at a ratio of 5:3:2. The total N fertilizer applied was 160 kg N hm\({}^{-2}\) for both rice seasons at ST2 and was applied at a ratio of 5:5. Mid-season drainage was the only time of drainage during the whole growing season, the timing of which is listed in Table 1. Natural drying downs were allowed in the AWD treatments.