Foliar N Supplementation Improves Rapeseed Transplanting Survival Rate and Yield

Transplanting shock induced by mechanical transplanting technique in dry land has a negative effect on the growth and grain yield of rapeseed (Brassica napus L.). We hypothesized that foliar nitrogen (N) supplementation plays a positive role in improving rapeseed transplanting survival rate and yield. The aim of the study was to elucidatethe morphological and physiological mechanisms of foliar N supplementation in rapeseed responding to transplanting shock. Through a 1-year pot experiment and a 2-year field experiment, foliar N supplementation at concentrations of 0, 2.5, 5.0, and 7.5 g N m−2 was set up to investigate the regulation of foliar N supplementation on the carbon (C) and N structure of seedlings before transplanting. Then we investigated the responses of morphological and physiological changes of shoot, root regeneration ability, transplanting survival rate, and grain yield to transplanting shock. The results showed that foliar N supplementation prior to transplanting increased the short-term activities of GS, GOGAT, and GDH, may improve the conversion of soluble sugar to soluble protein, increased N accumulation, and lowered the C:N ratio of rapeseed seedlings. Rapeseed seedlings with a low C:N ratio showed greater potential for root development after transplanting. Moreover, appropriate foliar N supplementation (2.5–5.0 g N m−2) not only up-regulated the positive feedback of osmoregulatory substances and antioxidant system for improving stress resistance, but also enhanced the synergistic growth of shoot and root by increasing root growth potential during transplanting shock. Therefore, the transplanting survival rate increased by 13.81–19.20%, and the grain yield increased by 25.15–30.56%. The optimal foliar N supplementation before transplanting may be used as a simple and effective agricultural measure to alleviate the negative effects of transplanting shock on rapeseed.