The characterization of an C 2 H 2 inhibition-based N 2 O production curve was conducted to estimate the N 2 O-reducing activity of denitrifying communities in soil. By normalizing the N 2 O production curve and calculating the value of the area under the curve (AUC), visual differences in the time course of N 2 O production in the presence and absence of an C 2 H 2 treatment were quantified in a series of experiments. The effects of liming and the addition of selected inorganic salts on the N 2 O-reducing activity of soil were analyzed. The average N 2 O/N 2 +N 2 O ratio, which is the ratio of the AUC value in the absence and presence of C 2 H 2 , indicated that a declining pH and the addition of Cl − and Ca 2+ resulted in the inhibition of the N 2 O-reducing activity, whereas liming (pH 6 using calcined lime, dolomite, charcoal, and ash of the charcoal) and SO 4 2− and Mg 2+ addition resulted in enhancing the N 2 O-reducing activity. Since the charcoal addition resulted in lowering the average N 2 O/N 2 +N 2 O ratio despite the fact that charcoal contained larger amounts of Cl − and Ca 2+ than SO 4 2− and Mg 2+ , the alkalinity of the charcoal (pH 9.3) rather than the types of anions and cations may be the most significant factor in the stimulation of the N 2 O-reducing activity. In addition, we found a non-linear negative relationship between the average N 2 O/N 2 +N 2 O ratios and the specific increasing rate constant of the N 2 O production curve. This result indicated that the application of a growth inhibitor of denitrifying communities into soil decreases the N 2 O-reducing activity of soil.