Abstract: Microorganism-driven nitrification is a key process in the nitrogen cycle. Soil ammonia oxidation is the first rate-limiting step in nitrification, and nitrogen application can affect soil ammonia-oxidizing microorganisms. The effects of different types of nitrogen fertilizers (urea, ammonium sulfate, and potassium nitrate) on soil ammonia-oxidizing microorganisms community and nitrification potential are still debated and can be a crucial reference for alleviating nitrogen loss and improving nitrogen cycle in farmland. In this study, four treatments i.e. no nitrogen fertilizer applied (CK), application of ammonium sulfate (AS), application of urea (UR), and application of potassium nitrate (PN) were established in a pot experiment using calcareous purple soil. Their effects on soil ammonia oxidation were investigated by measuring soil chemical factors, nitrification potential, and community structure and α diversity of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA). Our results indicated that, compared to CK treatment, AS and UR treatments significantly reduced soil pH by 2.52 and 0.32 (P<0.05), and significantly reduced carbon-nitrogen ratio by 40.0% and 20.0% (P<0.05), respectively, while significantly increased total nitrogen (TN) and ammonium nitrogen (NH₄⁺-N) contents by 53.6%−83.0% and 1 359.5%−1 740.4% (P<0.05), respectively. Compared to CK treatment, Soil alkaline hydrolyzed nitrogen (AN) and nitrate nitrogen (NO₃⁻-N) contents were significantly increased by 164.9%−233.1% and 434.6%−1 485.3% (P<0.05) under all three nitrogen fertilization treatments, while AS treatment significantly reduced soil available phosphorus (AP) content by 33.7% (P<0.05). The differences in soil organic carbon (SOC) under different treatments were not significant. The lowest nitrification potential was observed under AS treatment, which was reduced by 42% than that under CK treatment, while nitrification potential was significantly increased by 292.0% and 62.6% (P<0.05) under UR and PN treatments, respectively. Moreover, compared to CK treatment, the amoA gene abundance of AOA under AS and UR treatments significantly increased by 84.1% and 44.4% (P<0.05), respectively; the amoA gene abundance of AOB under AS treatment significantly reduced by 44.0% (P<0.05), and UR treatment significantly increased by 1 821.3% (P<0.05). Redundancy analysis showed that pH and NH₄⁺-N were the main factors influencing the AOA community structure, whereas AOB community structure was mostly influenced by C/N, SOC, and AN. Stepwise regression analysis showed that NH₄⁺-N and AN were the main factors influencing amoA gene abundance in AOA, while AP and AN were the main factors influencing amoA gene abundance in AOB. Partial least squares analysis showed that the amoA gene abundance of AOB, SOC, AP, AN, and pH had significant effects on soil nitrification potential (P<0.05). Our findings suggest that the application of ammonium sulfate significantly reduces the nitrification potential by increasing the AN content and reducing the AP content and amoA gene abundance of AOB, whereas urea application increases the nitrification potential by increasing AN content and amoA gene abundance of AOB. The AOB community was the primary driver of soil ammonia oxidation in the calcareous purple soil, and different nitrogen fertilizers exhibited different effects on the ammonia-oxidizing microbial community and nitrification potential. Ammonium sulfate application mainly reduced the nitrification potential by increasing AN content, reducing AP content, and the amoA gene abundance of AOB, whereas urea mainly increased the AN content and amoA gene abundance of AOB, leading to increased nitrification potential.