Abstract:

The conflict between rice cultivation and rice-rapeseed rotation stubble is a significant issue in the Yangtze River Basin, with delayed sowing of rapeseed often resulting in slow growth, poor development, and reduced yields. Therefore, optimizing nitrogen management is critical for promoting pre-winter growth and improving the yield of late-sown rapeseed. In this study, we used the variety “Huayouza 137” and conducted large-scale split-plot experiments in Wuhan and Huanggang, Hubei Province. Four nitrogen application rates were tested: N0 (0 kg hm^?2), N1 (150 kg hm^?2), N2 (225 kg hm^?2), and N3 (300 kg hm^?2). Additionally, three fertilization methods were employed: S1 (basal application), S2 (basal application: topdressing at the 3-leaf stage in a 5:5 ratio), and S3 (basal application: topdressing at the 3-leaf stage in a 5:5 ratio). The study investigated the effects of different nitrogen rates and fertilization methods on growth, lodging resistance, and yield of late-sown rapeseed. The results showed that as nitrogen application increased, rapeseed yields in both Wuhan and Huanggang followed a pattern of initial increase and then stabilization. The difference in seed yield between N2 and N3 treatments was not significant, with N2 treatment increasing yields by 20.76% in Wuhan and 15.02% in Huanggang compared to N1. Root neck thickness, number of green leaves, dry matter weight, and yield components followed a similar trend of initial increase and then stabilization. However, Basal and upper stem strengths increased initially and decreased later, while the basal and upper lodging indices increased with higher nitrogen application rates, indicating a greater risk of lodging and reduced resistance to lodging at higher nitrogen levels. Nitrogen use efficiency also followed a pattern of initial increase and then decrease, with the N2 treatment achieving 24.60% and 42.20% increases in nitrogen utilization efficiency compared to N1, and 11.58% and 9.04% increases compared to N3 in Wuhan and Huanggang, respectively. With changes in fertilization methods, rapeseed yield exhibited a trend of increasing and then decreasing. Under S2, yields in Wuhan and Huanggang increased by 11.72% and 11.92% compared to S1, and by 6.16% and 6.66% compared to S3. Root neck thickness, number of green leaves, dry matter weight, and yield components all reached their maximum under the S2 treatment. The basal and upper stem bending forces in both Wuhan and Huanggang first increased and then decreased, reaching their maximum under the N2S2 treatment. Conversely, the basal and upper lodging indices were highest under the N3S3 treatment, indicating poor lodging resistance and a higher risk of lodging under these conditions. Nitrogen partial productivity, nitrogen contribution rate, agronomic nitrogen use efficiency, and overall nitrogen use efficiency were all highest in the S2 treatment. There were no significantly different yield effects between N fertiliser rate and application method in this experiment, and the interaction effect between N fertiliser rate and application method was not significant. In conclusion, the N2S2 treatment (112.5 kg hm^?2 applied at the base and 112.5 kg hm^?2 applied at the 3-leaf stage) was the optimal nitrogen application strategy for late-sown rapeseed, balancing yield and lodging resistance. The findings from this study provide a theoretical basis and technical support for nitrogen management in late-sown rapeseed cultivation in the Yangtze River Basin. 

Key words: rapeseed, late-seeded, yield, nitrogen management mode, lodging resistance