Abstract: A field experiment was conducted to investigate influence of cropping systems on CH4 and N2O emissions from paddy field during the winter upland crop growing season.The experiment was designed to have five treatments,i.e.fallow,oil-seed rape with nitrogen(OR-N) or without nitrogen(OR-ck),wheat with nitrogen(W-N) or without nitrogen(W-ck).Results show that paddy field was obviously an N2O source,and a weak source or sink for CH4 as well during the winter upland crop season.Results also demonstrate that N2O emissions were significantly enhanced by nitrogen fertilization and peaked after each rainfall event,showing significant influence by soil water content.The seasonal mean of N2O fluxes for W-N and OR-N treatments was 18.51 and 13.47 μg·m-2·h-1,respectively,while the cumulative seasonal emission was 87.31 and 59.48 mg·m-2,respectively,being obviously higher than those in the control and fallow treatment.Though there was no significant difference in seasonal mean,there was in cumulative emission between wheat and oil-seed rape.On a 100-year time horizon,the integrated global warming potential of the treatments was assessed to be in the following sequence: OR-N>W-N>W-ck>fallow>OR-ck,in which N2O was the major contributor from the N fertilized treatments while CH4 was the major contributor from the no N treatments and that is unnegligible.

Key words: CH4, N2O, paddy field, upland crop, cropping system, fallow, wheat, oil-seed rape, integrative global warming potential