Abstract:Biochar can influence soil nitrogen nitrification and N2O emission. An indoor incubation experiment was conducted to study the net nitrogen nitrification rates and N2O emission in acidic (pH 5.10) and calcareous (pH 8.15) upland purple soils under different application rates of maize straw biochar (0, 1%, 2%, 5%, and 10% dry soil weight) with ammonium nitrogen fertilizer. The results showed that: 1) biochar addition inhibited net nitrogen nitrification rate in purple soils, compared with control treatment (no biochar application), biochar application reduced the average net nitrogen nitrification rate by 33.7%-93.7% in acidic purple soil and 7.5%-40.9% in calcareous purple soil. With the increase of biochar application rate, the inhibition was enhanced in acidic purple soil but irregular in calcareous purple soil. 2) Biochar addition significantly increased N2O emission, compared with the control treatment, cumulative N2O emission in acid purple soil decreased by 15.9% and 27.7% with 1% and 2% biochar addition rates, respectively. But cumulative N2O emission in calcareous purple soil increased by 60.1% and 93.2% with 5% and 10% biochar addition rates, respectively, and cumulative N2O emission of all biochar addition treatments in calcareous purple soil were significantly higher than that of the control treatment. 3) In general, biochar has no positive effect for calcareous purple soil in inhibiting nitrification and mitigate N2O emission, while 1% and 2% biochar addition rates are optimal for in acidic purple soil.