Optimized planting density and nitrogen rate improved grain yield of drip-fertigated maize by enhancing canopy structure and photosynthetic capacity

The planting density regulation and nitrogen fertilizer application have been widely utilized in maize (Zea mays L.) production. Improving the canopy structure can enhance the light energy interception and photosynthetic capacity of maize. However, the mechanisms by which canopy structure influences maize yield under varying planting densities and nitrogen rates remain poorly understood. A two-year field experiment was conducted in northwest China, with three planting densities (LD: 80,000 plants ha-1; MD: 100,000 plants ha-1; HD: 120,000 plants ha-1) and four nitrogen rates (N0: 0 kg N ha-1; N1: 120 kg N ha-1; N2: 180 kg N ha-1; N3: 240 N kg ha-1). Increasing planting density increased SDLA by 29.6 % in upper layer, 20.4 % in middle layer, and 12.7 % in lower layer compared to LD. Compared to N0, nitrogen application increased SDLA in middle layer by 30.0 %, in upper layer by 17.0 %, in lower layer by 11.6 %, separately. Compared to N0, the leaf base angle of the upper layer showed a significant increase by 6.4 % in N1, by 8.3 % in N2, and by 13.3 % in N3. Leaf base angle in N3 exhibited significantly increase by 10.5 % in middle layer and 11.1 % in lower layer. Compared to LD, the aboveground dry matter accumulation in the middle layer showed an increase of 23.0 % in MD, with no significant difference between MD and HD. In comparison to the aboveground dry matter accumulation of each layer under N0, the aboveground dry matter accumulation increased by 18.7 % in N1, 31.2 % in N2, and 33.3 % in N3, respectively. Increasing planting density led to a 10.8 % increase in IPAR in MD and a 17.1 % increase in HD over the entire reproductive period compared to LD, respectively. The MDN3 and MDN2 produced the highest grain yields in both years, at 17644 kg ha-1 and 16217 kg ha-1, respectively. Structural equation modeling indicated that nitrogen fertilization and planting density affected the intercepted light energy and ultimately dry matter accumulation and yield by influencing leaf basal angle and SDLA. This study contributes to a deeper understanding of the mechanisms behind yield variations under different planting densities and nitrogen rates, providing a scientific foundation for developing high-yield planting strategies.