Objectives Freezing during seedling and overwinter period of oilseed greatly impact the phosphorous nutrition and seed yield of oilseed rape production in the midstream region of the Yangtze River. This study investigated the mitigating effects of phosphorus fertilizer rates on the oilseed rape.

Methods According to the temperatures, 2022/2023 season was normal year, while 2023/2024 season was freezing year for oilseed production. Field experiments were conducted in 2022/2023 and 2023/2024 at Wuxue and Wuhan City of Hubei Province, respectively. Five P₂O₅ application rate treatments were setup, they were 0, 45, 90, 135, 180 kg/hm² in Wuxue site, and 0, 30, 60, 90, 120 kg/hm² in Wuhan site. The oilseed rape yield, yield components, and P uptake were investigated, and the mitigating effect of P fertilizer rates were assessed.

Results Compared with normal year, freezing reduced yield by 23.0%−58.6% and P accumulation by 31.1%−79.1%. Compared with no P control, P application mitigated the decline in yield and P accumulation in different degrees. The strongest mitigation effect in Wuxue site was at P₂O₅ 90 kg/hm², where the yield and P accumulation losses caused by freezing declined by 14.5 and 34.5 percentage points, and the greatest mitigation was observed in Wuhan site at P₂O₅ 120 kg/hm², with yield and P accumulation reduction of 13.3 and 24.5 percentage points, respectively. In Wuxue site, freezing during the overwintering period (minimum temperature <−5℃ for 3 days) and the bud-flowering period (minimum temperature <0℃ for 6 days) led to reduction of 38.7%−40.1% in pods per plant and 17.2%−28.0% in seeds per pod, the P accumulation on seeds were reduced greatly. While in Wuhan site, freezing lasted only 9 days during the overwintering period and 10 days during bud-flowering period, primarily reducing the number of pods per plant by 20.6%−58.7%. Increased P application rate mitigated the decline in the number of seeds per pod and 1000-seed weight in the Wuxue site, and mitigated the decline in the number of pods per plant in the Wuhan site.

Conclusion Freezing causes a decrease in oilseed rape yield and P accumulation, with the number of pods per plant being most affected. P fertilizer rates should be adjusted based on the soil and freezing conditions to improve the resilience and stability of oilseed rape production.