Effects of straw incorporation combined with nitrogen management on stem quality and lodging resistance of rapeseed following rice

Lodging is a major constraint limiting the yield and stability of direct-seeded rapeseed in the Yangtze River Basin. Straw incorporation from the preceding rice crop can influence lodging resistance in rapeseed by affecting carbon-nitrogen metabolism and stem morphology, especially when combined with tailored nitrogen management strategies. In this study, a split-plot design was used with the rapeseed hybrid Huayouza 62, based on a long-term rice-rapeseed rotation field experiment. The main plots comprised straw incorporation treatments (R0: no straw incorporation; R1: full straw incorporation). Subplots consisted of nitrogen application regimes: CK (conventional nitrogen rate of 240 kg hm^-2 with basal: seedling fertilizer ratio 6:4:0:0) and four 20%-reduced nitrogen treatments (N1, N2, N3, N4), maintaining identical total nitrogen reduction but differing fertilizer ratios (basal:seedling:bolting:flower fertilizer stages): N1 (10:0:0:0), N2 (6:4:0:0), N3 (6:2:2:0), and N4 (6:2:0:2). The effects of these treatments on stem cell wall composition at maturity, stem silicon and calcium content, and stem anatomical structure at flowering were evaluated. Compared with no straw return, full straw incorporation significantly increased aboveground fresh biomass by 29.1% and stem breaking strength by 23.3%. Increases were also observed in stem contents of cellulose (26.3%), total lignin (3.4%), pectin (30.6%), silicon (45.0%), and calcium (9.5%) (<italic>P</italic> &lt; 0.05), contributing to improved stem strength and toughness. However, the gains in plant height and biomass outpaced the improvements in stem strength, leading to a 7.9% average increase in the lodging index. Appropriate nitrogen allocation strategies improved stem structural quality and reduced lodging risk. Notably, the N3 treatment (192 kg hm^-2, applied as 6:2:2:0) under full straw return conditions reduced the actual lodging angle by 2.6%, increased stem breaking strength by 15.2%, and decreased the lodging index by 10.2% compared to the conventional treatment. These improvements were attributed to significant increases in stem cellulose, pectin, and calcium contents, as well as enhanced anatomical characteristics at flowering, including greater cortex and epidermis thickness, increased vascular bundle length and area, and a higher number of vascular bundles. A more uniform vascular bundle arrangement further contributed to improved stem mechanical strength and lodging resistance. Therefore, under high-density direct-seeded rapeseed cultivation with rice straw incorporation in the Yangtze River Basin, an optimized nitrogen regime of 192 kg hm^-2 (basal:seedling:bolting = 6:2:2) is recommended. This strategy not only reduces nitrogen input but also enhances stem strength and lodging resistance, thereby improving mechanical harvest efficiency while maintaining high yield and structural resilience.