Abstract: In order to find out the optimum sowing date of rapeseed after cotton spraying defoliant, Zhongshuang 11 was used as the test material. Five different sowing dates were set up（on October 11, October 14, October 17, October 20, October 23, expressed as T1, T2, T3, T4 and T5）. When the sowing date of T2 was completed, defoliant and clear water （CK） were spraying in each plot. The effects of cotton defoliant spraying on seed emergence rate and seedling quality of rapeseed at different sowing dates were studied. The results showed that, the seedling emergence rate and fresh weight of rapeseed seedlings at T1 and T2 were significantly lower than CK after spraying defoliant. Seed germination potential and seedling height of rapeseed at T1 sowing date were also significantly lower than CK. There were no significant differences in seedling emergence rate, germination potential, seedling quality and CK among other sowing dates. Different sowing date had no significant effect on seed germination potential, but had significant effect on seedling traits. The seedling quality between treatments and controls was the best at the seeding date of T3. It can be seen from the above that the optimum sowing time of rapeseed is T3, and spraying defoliant after direct sowing significantly affects the normal germination of rapeseed seeds and seedling growth.

Key words: cotton defoliant, sowing date, rapeseed, seed germination