Synergistic regulation of soil water and salt through mud blanket mulching and raised fields improves rainfed winter wheat yield on coastal saline-alkali land

Soil salinization induced by shallow saline groundwater severely limits rain-fed winter wheat yield in the Bohai Rim coastal region. Although mulching effectively suppresses salt accumulation, the interactive effect of mulching type and groundwater depth has not been clearly defined, and alternatives to plastic film are urgently required. In this two-year field experiment, mud blanket mulching (MBM), plastic film mulching (PFM), and no mulching (CK) were evaluated in combination with four raised-field heights (0, 0.5, 1.0, and 1.5 m) to assess their synergistic effects on soil water-salt dynamics, crop physiology, and grain yield. The results demonstrated that mulching and raised fields synergistically regulated the soil water-salt environment, and a significant interaction occurred between the two factors. Throughout the growing season, MBM reduced 0–20 cm soil salt content by 15.9–38.3%, increased grain yield by 53.7–70.2%, and enhanced water use efficiency by 16.4–388.5% compared with CK. Improved soil water-salt conditions increased leaf water potential, enhanced photosynthesis, and promoted dry matter accumulation. Path analysis showed that MBM increased yield primarily by increasing spike number through a population quantity-driven pathway, whereas PFM synergistically improved all three yield components. Grain yield exhibited a quadratic relationship with groundwater depth; the optimal depth shifted from 2.14 m under CK to 2.0 m under MBM and PFM. The greatest absolute yield gain occurred within a groundwater depth range of 1.7–2.2 m. Unlike PFM, MBM completely eliminated plastic residue pollution. Therefore, MBM represents a sustainable and eco-friendly mulching strategy that offers practical guidance for the efficient use of rain-fed saline-alkali farmland in comparable coastal areas.