Effects of a range of phosphorus levels on yield, phosphorus efficiency, and canopy sunlight interception in direct‐seeded winter rapeseed

Phosphorus (P) fertilization is a crucial practice for winter rapeseed (Brassica napus L.) production. With the shift to a direct seeding cropping system, the P fertilizer supply should be re‐evaluated for the requirement of direct‐seeded winter rapeseed in southwest China. A two‐factor field experiment was conducted in 2017–18 and 2018–19 in the region. The experiment aimed to investigate the responses of a wide range of P levels (0, 45, 90, 135, and 180 kg P ha−1) on yield, P‐efficiency, and canopy sunlight interception of direct‐seeded winter rapeseed. The results demonstrated that winter rapeseed yield was enhanced as the P fertilizer rate increased from 0 to 90 kg P ha−1, and excessive P fertilizer supply did not significantly contribute to higher grain yield at high P levels. Rapeseed produced 7.1–10.1 kg seed ha−1 to supply 1 kg P ha−1 average across different five P levels from 0 to 180 kg P ha−1. Phosphorus efficiency significantly firstly increased (0–90 kg P ha−1) and then progressively decreased with the rise of P levels (around 120 kg P ha−1). Greater P fertilizer rates were absorbed by the stem and pericarp while playing a negligible role in boosting winter rapeseed yield. When the target yield of 3000 kg ha−1 was set, the corresponding winter rapeseed canopy area index should be 1.42–2.71 to facilitate yield formation depending on the growth stages. Meanwhile, it intercepted 30.8%–88.7% of sunlight by the rapeseed canopy. A reduced P‐fertilizer level of 90–120 kg P ha−1 was recommended to obtain target yield with less environmental risks in direct‐seeded winter rapeseed planting regions. Core Ideas Greater P‐fertilizer rates did not contribute to a higher seed yield, only promoting the absorption of P by stem and pericarp. A reduced P‐fertilizer level attributed to relatively sufficient canopy area index and sunlight interception. A reduced P‐fertilizer level achieved target seed yield with lower environmental risks in direct‐seeded winter rapeseed.