The application of nitrogen(N) fertilizer to increase crop yields has a significant influence on soil methane(CH_4) and nitrous oxide(N_2O) emission/uptake.A meta-analysis was carried out on the effect of N application on(i) CH_4 emissions in rice paddies,(ii) CH_4 uptake in upland fields and(iii) N_2O emissions.The responses of CH_4 emissions to N application in rice paddies were highly variable and overall no effects were found.CH_4 emissions were stimulated at low N application rates(<100 kg N ha~(-1)) but inhibited at high N rates(>200 kg N ha~(-1)) as compared to no N fertilizer(control).The response of CH_4 uptake to N application in upland fields was 15%lower than control,with a mean CH_4 uptake factor of-0.001 kg CH_4-C kg~(-1) N.The mean N_2O emission factors were 1.00 and 0.94%for maize(Zea mays) and wheat(Triticum aestivum),respectively,but significantly lower for the rice(Oryza sativa)(0.51%).Compared with controls,N addition overall increased global warming potential of CH_4 and N_2O emissions by 78%.Our result revealed that response of CH_4 emission to N input might depend on the CH_4concentration in rice paddy.The critical factors that affected CH_4 uptake and N_2O emission were N fertilizer application rate and the controls of CH_4 uptake and N_2O emission.The influences of application times,cropping systems and measurement frequency should all be considered when assessing CH_4 and N_2O emissions/uptake induced by N fertilizer. The application of nitrogen (N) fertilizer to increase crop yields has a significant influence on soil methane (CH 4) and nitrous oxide (N 2 O) emission / uptake. A meta-analysis was carried out on the effect of N application on (i) CH 4 emissions in rice paddies, (ii) CH_4 uptake in upland fields and (iii) N_2O emissions. These responses of CH_4 emissions to N application in rice paddies were highly variable and overall no effects were found. CH_4 emissions were stimulated at low N application rates (<100 kg N ha -1) but inhibited at high N rates (> 200 kg N ha -1) as compared to N application (control). The response of CH_4 uptake to N application in upland fields were 15% lower than control, with a mean CH_4 uptake factor of-0.001 kg CH_4-C kg -1 N.The mean N_2O emission factors were 1.00 and 0.94% for maize (Zea mays) and wheat (Triticum aestivum ), respectively, but significantly lower for the rice (Oryza sativa) (0.51%). Compared with controls, N addition overall increased global warming potential of CH _4 and N_2O emissions by 78% .Our result revealed that response of CH_4 emission to N input might depend on the CH_4concentration in rice paddy. Critical part that affected CH_4 uptake and N_2O emission were N fertilizer application rate and the controls of CH_4 uptake and N_2O emission.The influences of application times, cropping systems and measurement frequency should all be considered when assessing CH_4 and N_2O emissions / uptake induced by N fertilizer.