A Meta-Analysis of the Effects of Increased Planting Density on Maize Yield in Northeast China

Increasing maize planting density is considered as a potential strategy for enhancing grain yield in Northeast China; however, its yield-enhancing effects and underlying regulatory mechanisms remain inadequately characterized. Based on 508 paired observations from 42 publications, this meta-analysis quantified the effects of increased planting density on yield components and elucidated the regulatory roles of environmental and agronomic factors. Results demonstrated that increased density intensified plant competition, raising grains per ear by 43.7% and 100-kernel weight by 6.7%. The optimal regional planting density was determined to be 89,622.6 plants ha^-1, achieving a peak yield of 12,143 kg ha^-1-significantly exceeding current conventional densities (49,000-65,000 plants ha^-1) and highlighting substantial yield potential. Although nitrogen (N) management did not alter peak yield levels, it significantly increased the optimal density threshold (reaching 99,600 plants ha^-1 under high N). Among environmental factors, mean annual precipitation (MAP) was the primary constraint: yield responses to increased density were negligible in arid regions (<400 mm); yield increase 4.0%, whereas optimal density (87,720 plants ha^-1) and peak yield (11,747.2 kg ha^-1) in high-rainfall regions (≥400 mm) were significantly higher than in arid regions. Soil organic matter (SOM) (>20 g kg^-1) and optimal bulk density (BD) (1.25-1.40 g cm^-3) synergistically enhanced optimal density and peak yield. This study confirms the substantial, yet context-dependent, yield potential of increasing planting density in Northeast China, providing a science-based framework for region-specific optimization.