Enhancing rapeseed yield and lodging resistance through combined inorganic nitrogen and long-term organic fertilizer application

To meet the increasing global demand for edible oils, enhancing seed yield and quality of winter rapeseed (Brassica napus L.) through organic fertilizers is a highly effective strategy. But the impact of long-term organic fertilizer on rapeseed lodging is most often ignored, leading to considerable knowledge gaps. To fill this gap, a 3year field experiment (from 2018 to 2021) started in 2012 was performed. The treatments comprised seven N fertilization levels (0, 60, 120, 180, 240, 300, and 360 kg N ha-1), in combination with long-term application of two rates of organic fertilizer (with and without). Seed yield, quality and lodging related attributes were quantitatively assessed. "Safety factor" (SF) method was employed in this study to assess the stem and root lodging resistance, which were quantificated by the value of SFs and SFr. Long-term application of organic fertilizer significantly increased seed yield and its associated traits such as the number of seed and pod and aboveground biomass, compared to no organic fertilizer application. Meanwhile, higher oil yield and better seed quality in terms of protein content, linoleic and palmitic acid were obtained when the seed yield was increased by long-term application of organic fertilizer. Lodging resistance (represented by SF) under long-term application of organic fertilizer was decreased when compared with no organic fertilizer, as was evident from the 30.3 % and 34.9% in SFs and SFr, respectively, across the three cropping seasons. It is crucial to consider the risk of stem and root lodging when implementing organic fertilizer applications to maximize rapeseed seed yield and quality. This study also illustrated a trade-off of seed yield with lodging risk. The results further revealed that root-soil cone diameter has a positive relationship with both root anchorage strength (Sr) and seed yield and is thus a key selection parameter for future's breeding programs to break this trade-off. In addition, prioritizing proper biomass allocation to root and stem tissues is imperative for enhancing lodging resistance, particularly against root lodging, in rapeseed plants.