Synergistic Enhancements in Maize Yield and Water Productivity: Dense Planting with Regulated Deficit Irrigation Versus Conventional Practice

Enhancing both grain yield and water productivity (WP) under water scarcity is a critical challenge for sustainable maize production. Conventional farmer practices—characterized by low planting density (D1: 9.0 × 104 plants·ha−1) and excessive irrigation (I5)—often limit the potential for both. To advance the high-density production system enabled by precision stage-specific regulation (HD-PSR), we conducted a multi-region field experiment across arid to sub-humid climates in Xinjiang, China. Treatments included region-specific full irrigation (I5) and four deficit levels (I1–I4, each reduced by 90 mm relative to I5). Compared with the conventional model (D1 + I5), the HD-PSR-based optimized model (D2, 12.0 × 104 plants·ha−1 plus regulated deficit irrigation, Iopt) synergistically increased grain yield by 18.8–25.0% and WP by 8.7–20.0% across sites, while saving 11.1–50.0% of irrigation water. This synergy was driven by improved canopy coverage and sustained dry matter accumulation under precision-regulated irrigation that maintained soil water storage at ~70% of field capacity, thereby reducing non-productive water losses (soil evaporation in arid/semi-arid areas and excessive transpiration in the semi-humid area). Our study provides a quantitative irrigation module for the HD-PSR and identifies a translatable soil water threshold (~70% FC) for sustainable intensification of maize in water-limited regions.