Long-term mulching reduces non-productive water use and increases transpiration and water productivity of maize in the semi-arid Loess Plateau

Mulching management is widely used to improve the productivity of dryland agriculture. To elucidate the eco-hydrological mechanisms governing dryland productivity, an eight-year field experiment (2018–2025) evaluated five treatments under varying rainfall patterns: ridge-furrow planting with film mulching on the ridge (RF), flat planting with full plastic film mulching (FPM), flat planting with full straw mulching (SM), flat planting with partial plastic film mulching (PPM), and flat planting without mulching (CK). Results indicated that mulching effects were contingent on rainfall patterns. Compared to CK, all mulching significantly alleviated topsoil (0–60 cm) moisture deficits. Crucially, deep soil moisture depletion (60–160 cm) induced by vigorous maize root uptake during the growing season under mulching was fully replenished during the mulched fallow periods through enhanced precipitation storage efficiency, preventing permanent soil desiccation. Thermally, plastic mulching increased growing degree-days by 120–260°C, whereas SM exerted a cooling effect of 133–157°C; both regulatory intensities were amplified in dry years due to reduced cloud cover and sparse canopy development, which enhanced solar radiation penetration. By integrating micro-lysimeters and the water balance method to partition evapotranspiration (ET) into evaporation (E) and transpiration (T), we determined that compared to CK, all mulching treatments optimized ET partitioning by suppressed unproductive evaporation, and boosting transpiration by 11.4–46.7%. Collectively, mulching increased biomass by19.4–40.0%, grain yield (GY) by 12.8–34.9%, and water productivity (WP) by 13.6–26.5%, compared to CK. Among them, FPM consistently achieved the highest physiological and agronomic performance with the smallest interannual variation. Partial Least Squares Structural Equation Modeling confirmed that optimized soil hydrothermal conditions drove maximum canopy expansion and robust transpiration, which essentially secured key yield components to maximize GY and WP. Consequently, FPM is the optimal strategy across all rainfall patterns to enhance climate resilience in semi-arid agriculture.