Tillage and nitrogen (N) management are key drivers of soil fertility and microbial processes in semi-arid agroecosystems. However, their combined long-term effects under the commonly adopted plastic film mulching system remain poorly understood. In this study, plastic film mulching was applied uniformly across all treatments to conserve soil moisture and temperature, reflecting standard agronomic practices in the semi-arid Loess Plateau of China. A multi-year field experiment was conducted to assess four tillage practices (conventional, rotary, no-tillage, and subsoil) combined with two N rates (200 and 300 kg N ha-1). Maize yield, soil properties, and N-cycling functional groups (amoA-AOA, amoA-AOB, nirK, nirS, and nosZ) were analyzed. Results showed that tillage and its interaction with N significantly influenced crop yield, soil fertility, and microbial community composition, whereas N rate alone had minimal effects. Subsoil tillage with 200 kg N ha-1 (T4N2) increased maize yield and biomass by 13.7 % and 13.2 %, respectively, compared with rotary tillage. No-tillage and subsoil tillage with moderate N input improved soil water content (15-20 %), total N (10-12 %), available P (18-20 %), SOC (12-15 %), and the C:N ratio (8-10 %) relative to rotary tillage. These practices enriched beneficial nitrifiers (Nitrosospira) and denitrifiers (Sinorhizobium, Thauera, Pseudomonas), which were positively correlated with nutrient availability and yield. Structural equation modeling revealed that tillage improved soil C and N status, which stimulated denitrifier diversity and indirectly enhanced maize productivity. Overall, conservation tillage with moderate N input under film mulching offers a practical strategy to improve yield, increase N use efficiency, and foster beneficial microbial communities in semi-arid drylands.