Abstract: The application of nitrogen (N) fertilizer results in decreases of soil pH, but its effects on CO₂ emission from soils with different inorganic carbon contents remain unclear. An closed-jar incubation experiment was conducted to examine the effects of N fertilizer and nitrification inhibitor (DCD) on soil pH and CO₂ emissions from three soil types with different contents of soil inorganic carbon (SIC), including paddy soil (PS), lime concretion black soil (CS), and eum-orthic anthrosols (AS). There were three treatments for each soil type, including control (N₀), 0.2 g·kg^-1 N fertilizer (N_0.2), and its combination with DCD (N_0.2+DCD). Soil pH, contents of mineral N (NH₄⁺, NO₃^-), and CO₂ emissions were measured. The results showed that N fertilizer addition significantly reduced soil pH and increased soil CO₂ cumulative emissions in each type of soil. Compared to control, the CO₂ cumulative emissions after 49 days incubation from the three soil types were enhanced by 39.4%, 23.4%, and 71.8% for PS, CS, AS soils, respectively. The soil pH of N_0.2+DCD for three soil types were significantly higher than N_0.2 after 49 days incubation, indicating that DCD application inhibited soil nitrification process. There were no significant differences in the mean CO₂ cumulative emissions of PS and CS soils between N_0.2 and N_0.2+DCD treatments; however, N_0.2+DCD treatment significantly reduced cumulative CO₂ emissions from AS soil by 12.5%. Soil inorganic carbon can effectively buffer soil acidification caused by N fertilizer addition. The CO₂ emission in calcareous soil following N addition is not only derived from the mineralization of soil organic carbon, but also from the dissolution of inorganic carbon. Given the large differences in soil inorganic carbon content in different regions of China, the problem of soil acidification and soil inorganic carbon pool consumption caused by long-term large amount of N fertilizer inputs deserve more attention.