3.2 Seasonal variation in CO2 efflux rate
The average CO2 efflux rate of each cultivation period was 13.8, 16.4, 21.5, and 16.6 mg CO2-C m−2 h−1 (first-year), 15.8, 19.4, 27.3 and 23.0 mg CO2-C m−2h−1 (second-year), and 20.1, 22.8, 35.9, and 34.8 mg CO2-C m−2 h−1(third-year) in the C, B, M and BM treatments, respectively (Fig. 1 and Table 3). The CO2 efflux rates were significantly impacted by treatments, time, and their interactions (Table 2). For all treatments, the average CO2 efflux rate in the cultivation period of the first year tended to be smaller than that of the second and third years. During the non-cultivation period, the average CO2 efflux rate was 9.8, 12.5, 12.5, and 11.7 mg CO2-C m−2 h−1(first-year), and 9.9, 10.5, 13.5, and 12.7 mg CO2-C m−2 h−1 (second-year), in the C, B, M and BM treatments, respectively (Fig. 1). The CO2efflux rates in all treatments were generally high during the rainy season and low during the dry season. The CO2 efflux rate in the C treatment was significantly and positively correlated with soil moisture throughout the experimental period (Fig. S2a).
During all cultivation periods, there were no significant differences in CO2 efflux rate between the C and B treatments (Table 3); however, the CO2 efflux rate in the B treatment tended to be higher than that in the C treatment. During all cultivation periods, the CO2 efflux rate in the M treatment was significantly higher than that in the C treatment, while the CO2 efflux rate in the BM treatment was significantly higher than that in the B treatment only at the cultivation period of the third year. There were no significant differences in CO2 efflux rate between the M and BM treatments, except for the cultivation period of the first year. During this period only, the CO2 efflux rate in the BM treatment was significantly lower than that in the M treatment (Fig. 1 magnified part). There was a significant interaction effect of biochar application and FYM application on CO2 efflux rate only at the cultivation period of the first year (Table S2).