Establishment Method Affects Oilseed Rape Yield and the Response to Nitrogen Fertilizer

Individual plant morphology and crop structure are contrasting between direct sown oilseed rape (Brassica napus L.) (DOR) and transplanted oilseed rape (TOR) in China due to altered plant density and growth duration. This study was conducted to compare the yield performance and response to N fertilizer between DOR and TOR. The effects of establishment method (direct sowing or transplanting) and N rate (0 or 180 kg N ha–¹) on yield, dry matter, and N uptake were determined through nine on-farm experiments in China. The DOR produced lower and more inconsistent yields compared with TOR under identical N rates. The yield reduction was 78.7% for DOR and 66.7% for TOR when N fertilizer was omitted, demonstrating that DOR was more sensitive to N deficiency. Furthermore, TOR outperformed DOR in terms of individual growth, dry matter yield, N uptake, harvest index, and N efficiency. Compared with the steady development of TOR, DOR exhibited fluctuating dry matter accumulation and N uptake during plant growth, mainly due to the differences in population dynamics and initial N concentration. The TOR plant density was consistent throughout the growing season, whereas DOR showed 73.3 and 38.5% plant loss in no-N and N-fertilized plots, respectively. Nitrogen application increased DOR plants survival based on improved individual growth. Hence, DOR exhibited a relatively greater response to N fertilizer. In conclusion, crop performance, yield level, and responses to N fertilizer were significantly different between DOR and TOR, suggesting that the N fertilizer management strategy should be adjusted depending on the establishment method.