The effects of nitrogen fertilizer application on methane and nitrous oxide emission/uptake in Chinese croplands

摘要

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(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.