Interactive Effects of Planting Density and Row Spacing on Maize Root Distribution and Yield

Effective spatial arrangement in maize population can reduce inter-plant competition, promote root development, and enhance nutrient uptake. This study aimed to clarify how planting density and row spacing affect maize growth and yield. A four-year field experiment (2011–2014) was conducted using three planting densities (50,025, 67,500, and 100,050 plants ha−1) combined with two row spacings. Grain yield increased with higher planting density, whereas plant dry weight and nutrient (N, P, K) contents declined. Higher density restricted root growth both vertically and horizontally, particularly in the 0–10 cm soil layer and inner root zone. Narrower row spacing increased grain yield, plant dry weight, and shoot nutrient contents and improved vertical and inner-zone root growth while reducing growth in the outer root zone. At the highest density, these effects were most pronounced in fine roots (<2 mm diameter), with significant increases in root length and surface area in the 0–10 cm layer in both vertical and inner horizontal zones. Overall, higher density intensified root competition and inhibited root development, whereas narrower row spacing alleviated such competition, enhanced nutrient acquisition, and improved crop yield. These results highlight the central role of fine roots in mediating maize responses to planting density and row spacing, suggesting that a moderate planting density (~67,500 plants ha−1) combined with narrower row spacing is optimal for balancing root development and yield.