Measurements of CH4and N20 emissions from rice paddies in Fengqiu, China

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Abstract
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 CH4 flux in 1994. The results showed that CH4 emissions were low compared with those recorded in previous reports and the means of CH4 fluxes ranged from 0.16 to 1.86 mg CH4 m-2 h-1 in the growing season (108 d). The lowest mean flux of CH4 was observed in the clayey plot in both years. Statistically, soil temperature and soil Eh at 5 em depth significantly affected the fluctuations of the CH4 flux measured in the morning and afternoon, but they were not the main factors controlling the seasonal variation of the CH. 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 CH4. In contrast, the studied plots had high emissions of N20, 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 N20 emission. Therefore, the mitigating effect of CH4 emission under the water regime would be offset by an increase in N20 emission. Rice fields where water management involves intermittent draining may contribute substantially to the total amount of N20 emitted to the atmosphere.