Measurements of CH_4 and N_2O Emissions from Rice Paddies in Fengqiu, China

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Methane emissions were measured by a closed chamber method in rice plots with sandy, loamy, and clayey soil, respectively, under a water regime consisting of a flooding and draining cycle in Fengqiu, Henan Province, China in 1993 and 1994. Nitrous oxide emissions were measured for every two measurements of CH_4 flux in 1994. The results showed that CH_4 emissions were low compared with those recorded in previous reports and the means of CH_4 fluxes ranged from 0.16 to 1.86 mg CH_4 m^<-2>h^<-1> in the growing season (108 d). The lowest mean flux of CH_4 was observed in the clayey plot in both years. Statistically, soil temperature and soil Eh at 5 cm depth significantly affected the fluctuations of the CH_4 flux measured in the morning and afternoon, but they were not the main factors controlling the seasonal variation of the CH_4 flux. Flooding and draining cycle, as well as high rate of water percolation and low organic matter content of the soils resulted in low emissions of CH_4. In contrast, the studied plots had high emissions of N_2O, ranging from -9.02 to 1,640 μg N m^<-2> h^<-1>, with arithmetic means of 168.8, 76.9, and 65.2 μg N m^<-2> h^<-1> in the sandy, loamy, and clayey plots, respectively, which were comparable in magnitude to those observed in cultivated upland soils. Flooding and draining cycle, i.e., dynamics of water status in the studied plots, was considered to be an important factor controlling N_2O emission. Therefore, the mitigating effect of CH_4 emission under the water regime would be offset by an increase in N_2O emission. Rice fields where water management involves intermittent draining may contribute substantially to the total amount of N_2O emitted to the atmosphere.
社団法人日本土壌肥料学会の論文

Measurements of CH_4 and N_2O Emissions from Rice Paddies in Fengqiu, China

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