Variety-Specific Row Spacing Optimization Improves Canopy Structure, Resource Use Efficiency and Grain Yield in Summer Maize Under Dense Planting

Optimizing row spacing can improve canopy structure and productivity in densely planted maize, but variety-specific responses under drip fertigation remain unclear. A field experiment was conducted in Baoding in 2024 and 2025 to evaluate three row spacing configurations (60 + 60, 40 + 80, and 30 + 90 cm) for three maize varieties (DH605, MY73, and JH517) at 90,000 plants ha−1. DH605, MY73, and JH517 achieved their highest yields under 40 + 80, 30 + 90, and 60 + 60 cm, respectively, with values of 15.0, 13.9, and 13.2 t ha−1, indicating clear variety-specific responses. Compared with the other configurations, the optimal row spacings increased leaf area index at maturity, ear-layer light transmittance, net photosynthetic rate, photosynthetic and antioxidant enzyme activities, post-silking dry matter accumulation, and resource use efficiency, while reducing malondialdehyde content. Yield improvement was mainly associated with higher kernel number per ear and thousand-kernel weight. Correlation and random forest analyses showed that grain yield was closely associated with these canopy, physiological, and resource-use traits, with water use efficiency being the strongest predictor. These results suggest that variety-specific row spacing optimization can enhance maize productivity by coordinating canopy architecture, post-silking physiological function, and resource use efficiency under drip fertigation.