How film mulching and organic fertilization regulate root-shoot architecture to improve drought resistance and productivity of dryland wheat

Film mulching technology and partial substitution of inorganic fertilizer with organic manure are mainstream agronomic strategies for raising crop productivity and water productivity (WP) in rain-fed farmland. However, few systematic studies have clarified their interactive effects on underground and aboveground growth balance, soil water consumption and yield formation of rain-fed winter wheat. To fill this gap, a three-consecutive-year fixed-site field experiment was conducted on the Loess Plateau with two soil surface covering patterns (bare land, P0; full plastic film mulching, P1) and three nitrogen application modes (single chemical fertilizer, CF; half organic substitution, CFM; pure organic manure, M). Field monitoring demonstrated that film mulching significantly increased soil water storage at all developmental stages of wheat, with more pronounced benefits under seasonal drought conditions. Compared with CF and M treatments, CFM significantly increased root length density (RLD), root diameter (RD), aboveground biomass, leaf area index (LAI), chlorophyll concent, and photosynthetic rate, while reducing the root–shoot ratio (R/S). Averaged three planting years, the P1-CFM integrated management obtained the highest grain yield and WP, with increases of up to 35.4% and 45.2% respectively, relative to the P0-CF combination under drought stress. Correlation analysis and structural equation modeling further revealed that optimized root morphology effectively boosted canopy physiological performance and modulated photosynthate allocation, thereby improving yield formation and water utilization. We conclude that the combination of plastic film mulching with 50% organic fertilizer substitution synergistically coordinates root and shoot growth, strengthens drought tolerance, and improves the productivity of rain-fed winter wheat on the Loess Plateau.