Impact of fertilization method on soil nitrous oxide emissions and ammonia volatilization during summer maize growth period

【Objectives】The temporal and spatial patterns of soil NH4+-N, NO2--N and NO3--N content variation under different nitrogen fertilization methods, and the soil air N2O and O2 concentrations were investigated in the present study. The aim is to explore the mechanism of soil NH3 volatilization and N2O emission. 【Methods】The tested N fertilization methods were: 1) local farmers' conventional practices in which urea is broadcasted on soil surface followed by irrigation (BC), 2) broadcasting urea on soil surface and followed by the application of nitrification inhibitor DCD on soil surface (BC+DCD), 3) band application of urea in the middle of two adjacent maize rows and backfilled with soil (Band). Field experiment was conduct in a summer maize field from July 23 to August 8, 2014. Crop yield and nitrogen uptake were measured in the ripe period. Soil N2O emissions were measured with static chamber-gas chromatograph (GC) method and NH3 volatilizations with PVC tube-venting method. Soil N2O and O2 content were measured with soil-air equilibration tube-GC and soil-air equilibration tube-pump determinator, respectively. 【Results】 The N2O emission and NH3 volatilization induced by farmers' practice was N 395 g/hm2 and N 22.9 g/hm2 respectively, the soil NO2--N showed accumulation to some extend. Compared with BC, the application of DCD precluded the accumulation of soil NO2--N in soil, reduced N2O emission by 89.4%,whereas increased NH3 volatilization by 27.1%; By contrast, band application of urea induced high soil NO2--N accumulation in the fertilizer band, doubled N2O emission, whereas reduced NH3 volatilization by 69.4%. O2 and N2O concentration is soil air was regulated by WFPS. When WFPS was over 60%, O2 concentration reduced while N2O concentration increased significantly in the 0-20 cm soil layer. A negative relationship was observed between N2O and O2 concentration in soil air. There was nether significant difference among the three treatments in maize yield, nor total N uptake of aboveground part. 【Conclusions】 The accumulation of NO2--N in soil induced by ammonium fertilizer relies on N management strategies. Band application of ammonium fertilizer increased NO2--N accumulation in soil and soil N2O emission significantly (P0.05). There is a trade-off between the nitrogen fertilizer management strategies with different mitigation objectives. The application of DCD reduced N2O emission while it increased NH3 volatilization on the other hand, whereas the band application of urea reduced NH3 volatilization but it increased N2O emission. The N2O emission and NH3 volatilization were both high in farmers' traditional practices. Band application with DCD may reduce N2O emission and NH3 volatilization in the same time, which needs further research.