Variation in the emission factor of N_2O derived from chemical nitrogen fertilizer and organic matter : A case study of onion fields in Mikasa, Hokkaido, Japan(Environment)

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Variability in the emission factors of nitrous oxide (N_2O) associated with the application of chemical fertilizer (EF_F) and organic matter (EF_O) were analyzed in two onion fields (GL, Gray Lowland soil [Gleysol; Food and Agriculture Organization/UNESCO]; BL, Brown Lowland soil [Fluvisol; Food and Agriculture Organization/UNESCO]) in Mikasa, Hokkaido, Japan. Nitrous oxide flux was measured using a closed chamber technique in four treatments (FOP, chemical nitrogen fertilization and organic matter application, with plants; F, chemical nitrogen fertilization only, without plants; OP, organic matter application only, with plants; C, control, no fertilization or organic matter application, without plants) for 4 years in GL (2000, 2003-2005) and for 1 year in BL (2005). The application rate of chemical fertilizer nitrogen ranged from 237 to 242kg N ha^<-1> year^<-1> in GL and was 284kg N ha^<-1> year^<-1> in BL; organic matter nitrogen ranged from 81 to 117kg N ha^<-1> year^<-1> in GL and was 181kg N ha^<-1> year^<-1> in BL. The emission factors (EF) were calculated using the equations: EF_F (%) = (N_2O emission in FOP-N_2O emission in OP)/(applied chemical nitrogen fertilizer) × 100 and EF_O=(N_2O emission in FOP-N_2O emission in F)/(applied organic matter nitrogen) × 100. The annual N_2O emissions for treatments FOP, F, OP and C were 7.2-17, 5.7-17, 3.2-9.9 and 2.0-12kg N ha^<-1> year^<-1>, respectively, in GL and 5.6, 2.8, 1.9 and 1.8kg N ha^<-1> year^<-1>, respectively, in BL. The EF_F ranged from 1.3% to 5.5% in GL and was 1.3% in BL. The EF_F was positively correlated with the mean annual air temperature (P < 0.01), suggesting that N_2O emission derived from chemical nitrogen fertilizer increases as air temperature rises. The EF_O, however, differed greatly between GL (ranging from -5.2% to 9.1%) and BL (1.5%). The EF_O was positively correlated with the mean annual relative humidity, although the correlation was not significant (P = 0.23). This finding suggests that much wetter climatic conditions may increase N_2O emissions derived from organic matter nitrogen. The estimated N_2O emissions based on these EF values and the rate of nitrogen application coincided well with the measured N_2O emissions in the FOP treatment in both soils.

Variation in the emission factor of N_2O derived from chemical nitrogen fertilizer and organic matter : A case study of onion fields in Mikasa, Hokkaido, Japan(Environment)

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