Abstract: Limited observation stations and high spatial heterogeneity of CH₄ flux are the challenges for the accurate estimation of CH₄ flux at waterair interface. Poyang Lake is the largest freshwater lake in China. In order to understand the autumn CH₄ flux at the waterair interface in the Lake, closed static chambers and gas chromatography were adopted to measure the CH₄ fluxes at the waterair interfaces in 4 inner lakes of the Lake in October 2010. The environmental factors including meteorological variables and sediment and water properties were also measured. The mean CH₄ flux in the Duchang inner lake was 0.26 mg·m^-2·h^-1, which was obviously higher than that in the inner lakes Xingzi (0.15 mg·m^-2·h^-1), Wucheng (0.13 mg·m^-2·h^-1), and Nanjishan (0.10 mg·m^-2·h^-1). The Lake had a mean CH₄ flux of 0.17 mg·m^-2·h^-1, with the coefficient of variation being 58.6%. The CH₄ flux was positively correlated with wind speed (P<0.01). After excluding the wind speed exceeding 5 m·s^-1, the contents of sediment organic carbon and water body ammonium were significantly positively correlated with the CH₄ flux. The dissolved organic carbon (DOC) content in water body was negatively correlated with the CH₄ flux (P<0.05). The accurate estimation of the CH₄ flux in the Lake would depend on more frequent measurements in larger areas.

Key words: nitrogen postponing application, winter wheat, water stress, photosynthesis, yield regulation.