| The experiment was conducted to investigate the effects of different forms of nitrogen application(ammonium, NH+4-N; nitrate, NO-3-N; and amide-N, NH2-N) and different concentrations(40, 200 and 800 mg/L) on N2O flux from the fluvo-aquic soil in a lab-simulated freezing and thawing process. N2O flux slowly decreased with soil freezing, and then increased slowly with soil thawing, reaching a peak at the initial thawing stage. The average N2O fluxes with addition of NH+4-N, NO-3-N and NH2-N are 119.01, 611.61 and 148.22 μg·(m2·h)-1 respectively at the concentration of 40 mg/L; 205.28, 1 084.40 and 106.13 μg·(m2·h)-1 at the concentration of 200 mg/L; 693.95, 1 820.02 and 49.74 μg·(m2·h)-1 at the concentration of 800 mg/L. The control is only 100.35 μg·(m2·h)-1. N2O flux with addition of NH+4-N and NO-3-N increased with increasing concentration, ranging from 17.49% to 425.67% for NH+4-N, and 563.38% to 1 458.6% for NO-3-N compared with control. There was a time lag achieving stable N2O emission flux with concentration increase. In contrast, by adding NH2-N to soil, N2O flux decreased with increasing concentration. In sum, inorganic nitrogen such as NH+4-N or NO-3-N fertilizer incorporated in soil enhanced the cumulative N2O flux from the fluvo-aquic soil relative to amide-N. This study suggested that ammonium and nitrate concentration in overwintering water should be less than 200 mg/L and 40 mg/L in order to reduce N2O emissions from soil, regardless of amide-N. |
