Methane Fluxes And The Influential Factors In The Typical Farmlands In The North China Plain

Using the enclosed chamber/GC technique, methane fluxes of winter wheat, summer maize and cotton were measured from June, 2005 to June, 2006 at the Yucheng comprehensive experiment station of the Chinese Academy of Sciences in Shandong Province. Methane exchange fluxes of soil were measured by small black chamber and methane exchange fluxes of soil-plant system was measured by big black chamber and transparent chamber. The results showed as the followings: Three kinds of crops showed similar seasonal variations of methane fluxes. In the wheat field, seasonal variations of methane fluxes in the soil-plant system were determined by the seasonal variation of air temperature and the phenology of winter wheat, In the cotton field, seasonal variations of soil methane fluxes were affected mainly by the temperature and most uptake peaks occurred in the day of high temperature. During the growing period of crops, the North China Plain is the sink of atmospheric methane. Diurnal variation of methane fluxes was not obvious in three kinds of farmlands. Plant and light accelerated the methane uptake flux of soil. There was an obviously parabola correlation between soil moisture and methane uptake flux. There was an obviously logarithm correlation between soil temperature and methane fluxes. When soil temperature at 5cm depth is between 0 to 25 °C, the relationship was stable. When soil temperature at 5cm depth is larger than 25 °C, the relationship weakened. There was an obviously parabola correlation between soil NH₄⁺ content and methane fluxes. The results showed that when it is above 3.1 mg·kg^-1, soil NH₄⁺ content can inhibit methane oxidation in the study. Measured data by using transparent chamber is close to actual methane fluxes of soil-plant system when the surface was covered by the crops.