Mitigating reactive nitrogen loss from soil is critical for sustainable agricultural intensification. However, the combined effects of the nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) and irrigation strategies on soil nitrogen dynamics remain unclear. A two-year experiment in the North China Plain evaluated how DMPP application, irrigation method (alternate vs. conventional drip irrigation), and irrigation quota (27 mm vs. 36 mm) affected soil NH₃ and N₂O emissions, physicochemical properties, enzyme activities, and microbial communities in summer maize systems. DMPP application, irrigation method and irrigation quota significantly affected soil urease and catalase activities, while alkaline phosphatase was mainly influenced by irrigation method (P < 0.05). Actinobacteriota and Proteobacteria dominated the microbial phyla, accounting for over 40 % of total relative abundance. Compared with treatments without DMPP, DMPP reduced N₂O emissions by 37.4–70.4 % but increased NH₃ volatilization by 13.5–18.7 % due to higher NH₄⁺-N concentrations and enhanced urease activity. Alternate drip irrigation (ADI) consistently lowered both NH₃ and N₂O emissions by 9.6–23.9 % and 17.8–37.6 %, respectively, compared with conventional drip irrigation, and when combined with DMPP under a 27 mm irrigation quota, achieved the lowest global warming potential and greenhouse gas intensity. Random forest regression analysis revealed soil water-filled pore space as the main driver of N₂O emission, while catalase and urease activities primarily controlled NH₃ volatilization. Integrating DMPP with ADI under 27 mm irrigation quota is recommended to mitigate gaseous nitrogen losses. Future research should examine microbial functional genes and long-term soil responses under integrated water-nitrogen management.