Post-Silking Nitrogen Topdressing Optimizes Nitrogen Accumulation and Enhances Yield in Densely Planted Maize

Nitrogen is pivotal for high-yield maize (Zea mays L.), but excessive nitrogen application and improper timing remain common in production. Clarifying nitrogen strategies and population nitrogen accumulation under high density is urgent. This study set two density levels (7.5 × 104 plants ha−1; 12.0 × 104 plants ha−1) and eight nitrogen management methods: the no nitrogen (N0), all-basal nitrogen (Fbase, total nitrogen: 360 kg ha−1), and post-silking topdressing methods (total nitrogen: 360 kg ha−1) with nitrogen proportions of 0% (F0%, post-silking topdressing: 0 kg ha−1), 20% (F20%, post-silking topdressing: 72 kg ha−1), 40% (F40%, post-silking topdressing: 144 kg ha−1), 60% (F60%, post-silking topdressing: 216 kg ha−1), 80% (F80%, post-silking topdressing: 288 kg ha−1), and 100% (F100%, post-silking topdressing: 360 kg ha−1). Fertilization was applied via drip irrigation. Results demonstrated that the highest yield was obtained under F60% at 7.5 × 104 plants ha−1 and under F40% at 12.0 × 104 plants ha−1. Appropriate post-silking nitrogen increments synergistically improved kernel number per ear and 1000-kernel weight. The post-silking nitrogen topdressing proportion significantly affected maize stand nitrogen accumulation. At maturity, the highest nitrogen accumulation was observed under F60% at 7.5 × 104 plant ha−1 density and under F40% at 12.0 × 104 plants ha−1 density. For the 7.5 × 104 condition, the duration of the rapid nitrogen accumulation period was extended by 11.9–39.2 days and maximum nitrogen accumulation increased by 15.52–57.20%; at 12.0 × 104, maximum nitrogen accumulation rose by 15.89–64.46%. In summary, appropriately increasing the proportion of post-silking nitrogen application can enhance maize yield, nitrogen accumulation, and nitrogen uptake efficiency. Specifically, a 60% post-silking nitrogen application ratio is recommended for a 7.5 × 104 plants ha−1 density and a 40% ratio for a 12.0 × 104 plants ha−1 density. These two strategies can significantly increase kernel number per ear and 1000-kernel weight, thereby improving maize yield and nitrogen use efficiency.