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).