[Characterization of CH4, N2O emission and selection of rice cultivars in double cropping rice fields]

Methane and nitrous oxide emission fluxes of rice cultivars in the double cropping rice fields were measured by static chamber-gas chromatography in field experiments. The results showed a single-peak pattern in seasonal variations of methane emission and a double-peak pattern in variations of nitrous oxide emission for the early season rice, and a single-peak pattern in variations of both methane and nitrous oxide emission for the late season rice. There was significant difference among the rice cultivars in the average emission fluxes of methane and nitrous oxide during the whole growing season. The ranges for the methane and nitrous oxide average emission fluxes were 0.58 mg x (m2 x h)(-1) and 5.89 microg x (m2 x h)(-1) for the early-season rice cultivars, and 4.06 mg x (m2 x h)(-1) and 5.70 microg (m2 x h)(-1) for the late-season rice, respectively. The ranges of GWP (global warming potential) contributed by the amount of greenhouse gases emission and GWP per unit yield of rice cultivars were 2.92 kg x hm(-2) and 0.097 kg x kg(-1) for the early-season rice cultivars, and 2 256 kg x hm(-2) and 0.28 kg x kg(-1) for the late-season rice cultivars, respectively. The GWP and GWP per unit yield of rice types were sorted in a descending order: traditional rice > the super hybrid rice > the hybrid rice. For the early season rice, the methane and nitrous oxide emission fluxes of the blank region without rice were 27.1%-31.8% and 33.6%-88.3% of those measured for the region with rice planted, respectively, whereas the corresponding percentages for the late season rice were 23.8%-28.8% and 38.6%-45.3%, respectively. Based on these results, Luliangyou No. 819, Jinyou No. 402 and Xiangzaoxian No. 24 were selected as suitable early-season rice cultivars, whereas Yueyou No. 9113 and Xiangwanxian No. 12 should be chosen for late-season rice planting.