Fig 1.
Main processes produce N2O in soils.
Table 1.
Soil properties of the sampling area.
Fig 2.
Variations of soil N2O emissions applied with different forms and levels of N addition among five–year experimental period.
L: 50 kg N ha–1 yr–1; H: 150 kg N ha–1 yr–1. Error bars indicate the standard error of the mean (n = 9).
Table 2.
Summary of repeated measures ANOVA results (F values) indicating the effects of different forms and levels of N addition and experimental time on temporal variation of soil N2O emissions and annual cumulative N2O emissions.
Table 3.
Cumulative N2O emission (kg N ha–1 yr–1) from different N addition treatments plots.
Fig 3.
Water filled pore space (WFPS), soil temperature and air temperature in the observed period.
Table 4.
Summary of repeated measures ANOVA results (F values) indicating the effects of different forms and levels of N addition and experimental time on soil temperature at 5 cm soil depth (ST), water-filled pore space (WFPS), and the concentrations of soil inorganic N (NO3− and NH4+).
Fig 4.
Variations of soil NH4+–N concentrations applied with different forms and levels of N addition among five–year experimental period (a) NaNO3 addition plots; (b) (NH4)2SO4 addition plots; (c) NH4NO3 addition plots. L: 50 kg N ha–1 yr–1; H: 150 kg N ha–1 yr–1. Error bars indicate the standard error of the mean (n = 9).
Fig 5.
Variations of soil NO3––N concentrations applied with different forms and levels of N addition among five–year experimental period (a) NaNO3 addition plots; (b) (NH4)2SO4 addition plots; (c) NH4NO3 addition plots. L: 50 kg N ha–1 yr–1; H: 150 kg N ha–1 yr–1. Error bars indicate the standard error of the mean (n = 9).
Fig 6.
Relationships between soil N2O emissions and soil NH4+–N concentration (a), soil NO3––N concentration (b), soil temperature (5 cm depth) (c), WFPS (10 cm depth) (d).