Effect of soil water contents in the non-rice growth season on CH4 emission during the following rice-growing period

A pot experiment was carried out to investigate the effect of soil water content in the non-rice growth season (winter season) on CH4 emission during the following rice-growing period. The results showed that CH4 fluxes increased significantly with the increase of soil water content in the winter season, except air-dry water condition. The mean CH4 fluxes of treatments with soil water contents in the winter of 3.89-5.37% (air-dry), 25-35%, 50-60%, 75-85% and 107% (flooded) of field water capacity (FWC) were 13.04, 4.04, 8.61, 13.26 and 20.47 mg m(-2) h(-1), respectively. Antecedent soil water contents also markedly affected temporal variation patterns of CH4 fluxes and soil redox potential (E-h) during the rice-growing period. The higher soil water contents in the winter season were, the quicker soil E-h decreased, and the earlier CH4 emission occurred after rice transplanting, except air-dry water condition. Though the seasonal mean CH4 flux was significantly correlated with the seasonal mean soil E-h, the seasonal variation of CH4 fluxes was not always significantly correlated with soil E-h. For the treatment flooded in the fallow season, there was no significant correlation between CH4 flux and soil E-h, but there was significant correlation between CH4 flux and soil temperature during rice growth season. In contrast, for the other four treatments, it was soil E-h, not soil temperature that significantly affected the temporal variation of CH4 emissions. Soil water contents in the fallow season significantly influenced concentrations of soil labile organic carbon (including undecomposed plant debris), active Fe and Mn immediately before rice transplanting. The mean CH4 fluxes during rice-growing period were significantly correlated with soil labile organic carbon contents (positively) and contents of soil active Fe and Mn (negatively).