Promoting rapeseed yield: Improving canopy structure and formation of large pod via adjusting planting density

Increasing planting density is a common practice to enhance rapeseed (Brassica napus L.) yield via an increase in pod quantity. However, excessive density may lead to a deterioration in pod quality. Therefore, we hypothesized that improving pod quality based on a certain level of pod quantity could further increase seed yield. A randomized block experiment was conducted with five density levels (2.4, 3.6, 4.8, 6.0, and 7.2 × 10⁵ plants ha⁻¹, referred to as D1, D2, D3, D4, and D5) using two hybrid varieties of Qinyou10 and Ningza1838. The plot seed yield reached the maximum value in D2 or D3, and there was no significant difference between these two density levels. An increase in planting density resulted in a decrease in canopy thickness, but an increase in lodging angle and pod density. According to the number of seeds per pod, the pods were categorized into low-productive pod (≤14), middle-productive pod (15‒17), and high-productive pod (≥18). The number of high-productive pod in D2 and D3 ranged from 48.15 × 10⁶ to 54.22 × 10⁶ ha⁻¹, accounting for 53.76%‒63.28% of the total pod number and 76.89%‒82.83% of the total seed yield. With the planting density increasing from D3 to D5, there was a significant transition from high-productive pod to middle-productive and low-productive pods, causing a decrease in seed yield. Therefore, when the seed yield was targeted as 4500 kg ha⁻¹, the suitable planting density ranged from 3.6 × 10⁵ to 4.8 × 10⁵ plants ha⁻¹, and the optimal number of pods in population ranged from 83.0 × 10⁶ to 94.0 × 10⁶ ha⁻¹, and the quantity proportion of high-productive pod maintained >50%. This study provides a guide for high-yield cultivation of rapeseed in China and presents a novel approach to promoting a potential yield of rapeseed.