Effects of nitrogen rate on growth and quality of rapeseed blanket seedling for mechanized transplanting

Cultivating a high quality rapeseed blanket seedling is crucial if the mechanized transplant of rapeseed is to become an effective part of oilseed production in China. Nitrogen (N) strongly affects the growth and quality of the rapeseed seedling. This study investigated the agronomic traits, physiological indexes, the surviving number of blanket seedlings, and the survival rate after transplanting two canola (Brassica napus L.) cultivars (Ningza 1838 and Yangyou 9) treated with five N rates (0, 0.5, 1.0, 1.5 and 2.0 g N per tray). Plant height, leaf age, leaf area, collar length, fresh and dry weights, moisture content, and N concentration in root and shoot all increased as the N rate increased. The survival number, collar diameter, root to shoot ratio at the 30th day after sowing and the survival rate at the 10th day after transplanting increased at first then decreased as N rate consecutively increased. The survival number and survival rate under the 1.0 and 1.5 g N per tray treatments were most improved amongst N treatments, although there was no significant difference between these two N treatments. This suggests that to achieve high-quality blanket seedling needed for mechanized transplanting, the application of N at rates of 1.0 to 1.5 g N per tray at the one-leaf and one-heart stages is recommended.