Optimized planting density and organic fertilizer substitution improve maize yield by enhancing dry matter translocation and grain-filling characteristics.

INTRODUCTION: Increasing planting density and partial substitution of chemical fertilizer with organic fertilizer are important strategies for improving maize yield. However, how their interaction regulates dry matter accumulation, translocation, and grain-filling characteristics to affect yield formation remains unclear. METHODS: A three-year field experiment (2023-2025) was conducted with three planting densities (70,000, 100,000, and 130,000 plants ha-1) and four fertilization treatments (no fertilization, chemical fertilizer only, and 17% and 34% organic fertilizer substitution) to evaluate canopy light interception, dry matter accumulation and translocation, grain -filling characteristics, and yield formation. RESULTS AND DISCUSSION: The results showed that 17% organic fertilizer substitution improved radiation use efficiency at silking by 7.76%-20.42%. Although increasing planting density reduced per-plant dry matter accumulation by 20.29%-36.53%, 17% organic fertilizer substitution improved dry matter partitioning and partly alleviated the reductions in grain-filling duration and grain weight. Random forest analysis identified aboveground biomass accumulation as the primary predictor of yield and showed that maximum and mean grain-filling rates contributed more strongly to yield prediction than the active grain-filling period. Partial least squares path modeling further revealed that yield reduction under high density was mainly attributed to suppressed post-silking dry matter accumulation, while fertilization promoted dry matter accumulation and translocation, thereby strengthening their positive contributions to grain filling and yield formation. Across three growing seasons, 100,000 plants ha-1 with 17% organic fertilizer substitution (D2F2) increased yield by 7.46%-23.83% compared with conventional management (D1F1). Therefore, D2F2 may serve as a promising management option for improving dry matter translocation, grain filling, and maize yield. These results provide valuable references for optimizing density-fertilization management in semi-arid maize production systems.