Improved canopy structure and post-silking productivity contribute to higher grain yield of densely planted summer maize

Summer maize production in the North China Plain is constrained by rainy weather, low irradiance, and conventional water–fertilizer management. High planting density increases yield potential but may intensify interplant competition, impair canopy light distribution, and weaken leaf function after silking. This study aimed to identify key canopy structural and post-silking traits associated with grain yield and resource use efficiency in densely planted summer maize under drip fertigation. A two-year randomized complete block field experiment was conducted with widely grown cultivars from the Huang-Huai-Hai region. At 97,500 plants ha⁻¹, cultivars within each year were classified into high-yielding (H1), medium-yielding (H2), and low-yielding (H3) groups based on grain yield, and key traits and their relationships were analyzed. H1 achieved a mean yield of 14.3 t ha⁻¹, significantly higher than those of H2 and H3, mainly due to coordinated increases in kernels per ear, 1,000-kernel weight, and kernel number per unit area. H1 had a smaller leaf angle above the ear and a greater leaf orientation value, indicating compact, erect architecture. H1 exhibited a higher leaf area index (LAI) at silking and maturity and greater light transmittance at the ear layer in both years. After silking, H1 maintained greater leaf area duration, a higher leaf photosynthetic rate, higher phosphoenolpyruvate carboxylase (PEPC) activity, greater superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, and lower malondialdehyde (MDA) content. Post-silking dry matter accumulation accounted for 64.1% of total dry matter at maturity, with a harvest index of 0.54. Radiation and heat use efficiencies were 25.1 and 23.9% higher than those of H3, respectively. Correlation analysis showed that leaf angle above the ear was significantly negatively correlated with grain yield. Structural equation modeling (SEM) further indicated that leaf angle above the ear was indirectly associated with harvest index, radiation use efficiency, and grain yield through LAI at silking and post-silking dry matter accumulation. Overall, high-yielding populations were characterized by compact architecture, favorable canopy light transmittance, sustained leaf function after silking, greater post-silking dry matter accumulation, and higher resource use efficiency. Nongda 372, Guansheng 601, MY73, and Longxi 109 showed stable performance in this study and warrant further testing across locations.