High planting density benefits to mechanized harvest and nitrogen application rates of oilseed rape (Brassica napusL.)

To evaluate the effects of planting density and nitrogen (N) application rate on agronomic characters, yield and N use of oilseed rape (Brassica napus L.), a split plot experiment was carried out. Two planting densities (1.5 × 105 plant ha−1 and 4.5 × 105 plant ha−1 as main plots) and four N rates (0, 90, 180 and 270 kg ha−1 as sub plots) were designed for two cultivars of Brassica napus. Results indicate that increased planting density could lead to decreased plant height, branch number, canopy layer thickness, effective siliques per plant and harvest index, while branch height and N use efficiency increase. Under a single density, plant height, branch height, branch number, effective siliques per plant and yield increased with increased N application, but the oil content and N use efficiency decreased. For the same target yield (plateau yield) obtained in low-density planting, the N fertilizer requirement decreased by 22.8% and 25.4% in high-density planting in two experimental sites. On the whole, these results demonstrate that increased plant density can improve rape adaptability for mechanized harvest by regulating plant structure, decreasing the N requirement for reaching a target yield and increasing N use efficiency.