Soaking seeds of winter rapeseed with Quizalofop-P-Ethyl alters plant growth and improves yield in a rice-rapeseed cropping system

Intercropping is an effective strategy to maximize production potential, profits, and land use efficiency. Sowing winter rapeseed in rice fields is a common cultivation technique in the Yangtze River basin in China, which is the world's largest region for rapeseed production. However, the 10-15 days crop overlap in rapeseed-rice cultivation results in low and unstable yields. In this study, we investigated, using both pot and field experiments, whether presoaking oil rape seeds with Quizalofop-p-ethyl (QPE) improved winter hardiness and yield. For the field trials, rapeseed was cultivated during two growing seasons from 2009 to 2011, in no-tillage fallow rice fields at the experimental site of Wuhan. Without QPE application, seedling quality was low for rapeseed sown in pots, and grown in shady conditions, or in the fallow rice field. Seedlings showed excessive elongation of the crown, resulting in low yields and yield-related traits at maturity. Soaking seeds in QPE improved the growth and survival of rapeseed seedlings, and improved their length, weight, and root neck diameter traits. Furthermore, the treatment decreased crown length during winter. Overall yield and related traits were enhanced by the QPE treatment. The most effective concentration of QPE was 120 ppm. Storing seeds for 2-10 months after soaking in QPE reduced any inhibitory effect of the treatment on germination rate and plant height. Our analyses demonstrated that treating seeds with QPE (120 ppm) increased the yield of rapeseed in a rice-relay cropping system.