Using the closed chamber method, the methane emission rate from rice paddies was measured during three complete vegetation periods from 1990 to 1992 in the Beijing area. The emission level of this region was found between 15.0 mg/m2/h and 20.4 mg/m2/h. The methane emission rate showed a strong diurnal variation with the maximum and minimum emission rate in the afternoon and in the morning, respectively. The diurnal methane emission rate closely correlated with soil temperature after the tillering stage. A study on the effect of four kinds of chemical fertilizers (ammonium sulfate, urea, ammonium phosphate, ammonium bicarbonate) was carried out in 1991 and 1992. Application of ammonium sulfate and urea resulted in a reduction of methane emission, while application of ammonium phosphate enhanced the methane emission during the effective period of a chemical fertilizer. No significant influence of ammonium bicarbonate was found. Reasonable application of some types of chemical fertilizers in 1992 resulted in a significant reduction of total methane emission from rice paddies.
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