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INCREASING population and demand for food are placing unprecedented pressure on agriculture and natural resources 1,2 . Agriculture is estimated to account for 10-12% of anthropogenic emissions of greenhouse gases (GHGs) worldwide, including 60% of global nitrous oxide (N 2 O) emissions and 50% of methane (CH 4 ) emissions 3 . Rice paddies are considered one of the most important sources of atmospheric CH 4 , but they also emit N 2 O and the intensity of emissions is related to the nitrogen (N) fertilizer application rate 4,5 . The increasing demand for rice in the future has raised tremendous concerns about increasing GHG emissions 6,7 . Rice paddies could contribute to more than 80% of CH 4 and N 2 O emissions driven by microbial activities. The application of N fertilizer is one of the primary methods for enhancing rice production. Field measurements have reported that N fertilization significantly stimulated CH 4 and N 2 O emissions 4 , but some studies found reduction in CH 4 emissions with N fertilizer application 8 . Based on these existing data, it is difficult to determine an optimal rate of N fertilization for high productivity while reducing GHG emissions. Thus information regarding factors influencing rice yield and tendency to reduce GHG emissions is urgently needed to aid cropping technique innovation. Furthermore, it is important to explore the relationship between CH 4 and N 2 O emitted from rice fields. Thus the present study is aimed (i) to assess the actual relation between CH 4 and N 2 O emitted from rice and (ii) to scale rice productivity under varied CH 4 and N 2 O emission potentiality.

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