Plastic film mulching and fertilizer application are important practices for increasing yield in dryland agriculture. Balancing yield gains with greenhouse gas (GHG) mitigation remains a key challenge in semi-arid regions. Based on a long-term factorial field experiment of plastic film mulching and nitrogen application on the Loess Plateau, this study evaluates how management practices and climatic conditions interactively affect maize yield, GHG emissions, and soil properties, and elucidate the water-soil-GHG coupling mechanisms. The results showed that the optimal nitrogen rate differed between plastic film mulched and bare soils under contrasting rainfall. An overall range of 150-225 kg N ha-1 achieved good balances between high yield with low emissions. Under plastic film mulching, 225 kg N ha-1 provided the best trade-off between yield and CFy in both normal and dry years, whereas for bare soil it was 150 and 225 kg N ha-1 , respectively. Plastic film mulching increased total GHG emissions, yet yield-scaled carbon footprint (CFy) responses were climate dependent. CFy was generally higher than under bare soil in 2023, whereas it was mostly lower in 2024 (-7.8%-2.5%) under plastic film mulching. Network analysis and structural equation modeling (SEM) revealed the underlying water-soil-GHG coupling mechanisms. Climatic background, together with plastic film mulching and nitrogen input, reshaped the soil coupling structure by stabilizing the hydrothermal environment, alleviating microbial water stress, and enhancing synergies within nitrogen and microbial pools. These processes determined CO2 responses to heat and moisture and regulated pulse and background N2O emissions across different growth stages. Overall, this study demonstrates that the environmental benefits of plastic film mulching-nitrogen strategies depend on interannual water availability, and provides practical recommendations and theoretical support for sustainable agriculture in semi-arid croplands.