Figure 1. CH₄, CO₂ and N₂O concentrations (mean ± standard deviations, n = 3) in soil air at various soil depths in a winter wheat–summer maize double cropping rotation receiving 0, 200, 400 and 600 kg of N ha⁻¹ year⁻¹, in 2007–2008 (A); NO₃-N contents (mean ± standard deviations, n = 3) at various soil depths as function of N fertilizer application rate, in 2007–2008 (B); Profiles of concentration and annual cumulative flux of CH₄, CO₂ and N₂O, in 2007–2008 (mean ± standard deviations, n = 4).

Same letters next to the bars indicated no significant differences between slope positions (P<0.05). (C). Note the differences in X-axes.