Context: How to reduce the loss of reactive nitrogen (RNL), increase the nitrogen fertilizer use efficiency, and alleviate the negative impacts of nitrogen fertilization on the environment has always been the focus of scientific research. Currently, the responses of RNL and nitrogen cycling microorganisms (NCM) in aeolian sandy soil to different levels of subsurface drip fertigation and the mechanisms in temperate arid regions are still unclear. Objective: The aim was to clarify the effects of different levels of subsurface drip fertigation on the soil RNL and NCM in alfalfa fields. Methods: A two-year field experiment was conducted in Yinchuan, an arid region of northwest China, with two subsurface drip irrigation levels (525 and 700 mm) and three nitrogen application rates (0, 150, and 300 kg N ha-1). Results: The pulse emissions of N2O and NH3 significantly increased after irrigation and nitrogen fertilization. Nitrogen fertilization significantly increased N2O and NH3 emissions under the two soil moisture conditions compared with the control, especially the W2N2 treatment, due to that the increase in soil NH4+-N content led to changes in the abundance of nitrogen cycling-related functional genes. The quantities of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) reflected their contributions in the ammonia oxidation, but this contribution varied depending on specific soil environmental conditions. Under low soil NH4+-N content conditions, AOA was more active than AOB and contributed more to total ammonia oxidation. Interestingly, at the high irrigation level (700 mm), nitrogen fertilization had a weaker effect on bacterial diversity than irrigation; Irrigation had a more direct and positive effect on the number and diversity of soil bacteria by increasing soil moisture content and changing soil physicochemical properties. At the high nitrogen application rate (300 kg N ha-1), AOB contributed more to the ammonia oxidation than AOA, which indirectly increased the relative abundance of Actinobacteriota, and led to greater RNL by reducing the abundance of AOA and Firmicutes. Conclusion: The irrigation and nitrogen fertilization affected the diversity and composition of bacterial communities in aeolian sandy soils, and changed N2O and NH3 emissions by changing the abundance of NCM. Significance: This study will deepen our understanding of the regulation of subsurface drip fertigation on soil microorganisms and N2O and NH3 emissions in grassland ecosystems.