Improving agroecosystem sustainability requires optimizing water and nitrogen use efficiency while minimizing environmental impacts. A two-year field study (2022-2023) was conducted on China's Loess Plateau to investigate the effects of three mulching practices (black film, white film, and no mulching) combined with four nitrogen management strategies (conventional urea at 270 kg N ha-1, optimized urea at 200 kg N ha-1, and controlled-release urea at 170 and 140 kg N ha-1) on soil hydrothermal dynamics, total dry matter production (DMP), evapotranspiration (ETc act), water productivity (WP), and nitrogen use efficiency. White film mulching significantly improved the early-season soil thermal environment compared to no mulching. Crucially, film mulching substantially enhanced DMP and multifunctional water WP without increasing seasonal ETcact. White film, in particular, achieved the highest DMP and water productivity metrics among all treatments. The 170 kg N ha-1 controlled-release urea fertilization maintained yield while reducing N input by 37 %, decreasing soil nitrate N accumulation by over 60 %, and enhancing partial factor productivity of N (PFPN). Structural equation modeling indicated that improving soil hydrothermal conditions and regulating evapotranspiration were key factors associated with synergistic improvements in WP and PFPN. The combination of white film mulching and reduced-dose controlled-release urea (170 kg N ha-1) offers an effective strategy to enhance WP and support yield stability in water-limited agroecosystems. These results provide a practical management strategy for sustainable agricultural intensification in semi-arid, rainfed agroecosystems.