Excessive fertilizer application to cropland results in high N 2O emissions; thus cropland becomes an important source of greenhouse gas (GHG) emissions. To reduce N 2O emissions, an experiment was conducted to investigate the effects of fertilizer types on N 2O emissions in spring maize fields in northern China, which was monitored continuously by automatic measurement system. The responses of grain yield, in addition to N 2O emissions, were examined to explore feasible strategies to reduce N 2O emission. Four fertilizer application treatments including no fertilizer application treatment (control), urea treatment (U), urea and phosphorus treatment (NP), and nitric phosphate treatment (NOP) were designed in field experiment. Results showed that the total N 2O fluxes in each treatment were 0.21 kg N/ha in the control, 1.19 kg N/ha in U, 0.93 kg N/ha in NP, and 0.69 kg N/ha in NOP treatments, respectively. The N 2O emissions were mainly influenced by fertilizer application, irrigation, precipitation and soil temperature. Soil N 2O uptake was observed during the late growth stage of spring maize when soil mineral N was lower than 7 mg N/kg. The N 2O emission factor (EF) of each fertilizer treatment was lower than 1% which was suggested by the Intergovernmental Panel on Climate Change (IPCC). This means that the default EF should not be used for estimation of the regional N 2O fluxes in spring maize fields in northern China. Phosphorus fertilizer not only could reduce the N 2O emission but also increase maize grain yield, whereas nitric phosphate was significantly more effective than urea in reducing N 2O emissions. Evaluation based on crop yield and N 2O emissions showed that NOP treatment was a better management practice in the sense that, when compared to U and NP treatments, it reduced not only N 2O emission by 42% and 26%, respectively, but also the farmers' expenditure reduced by 15% and 30%, while crop yield was maintained.
