Optimum Transplanting Date for Rape Forage and Grain Yields in the Ridge Culture Place Planting System on the Yangtze River Delta

The ridge culture place planting system (RCPPS) is a promising technique for planting rapeseed that can promote the growth of rapeseed by late rice stubble, which has been widely adopted in the Yangtze River delta. To determine the optimum planting date for rape (Brassica napus L.) forage and grain yield in an intensive rice–rape rotation system, a field experiment was conducted with five transplantation dates (from 20 October to 30 November at 10 day intervals) in RCPPS. The forage/grain yield, nutrition, and growth parameters were analyzed. At podding, rape biomass yield was highest, and no significant differences were found among treatments. It was around 12.0% crude protein, 11.4% ether extract, 38.8% neutral detergent fiber, and 34.9% acid detergent fiber. In the treatments of 20 and 30 November, crude protein content increased and acid detergent fiber content decreased significantly. Compared with 20 October, the grain yield of rape transplanted in November decreased significantly by 17.2% to 22.5%. The grain yield was significantly correlated with the number of secondary branches, pods, and seeds. At the final flowering stage, rape transplanted in November had noticeably reduced leaf growth, rhizome width, and yield than 20 and 30 October. Overall, for multiple uses of rapeseed in the Yangtze River delta belt with RCPPS, it is optimal to plant in mid to late November for forage use with higher nutritional value, being coordinated with the previous rice crop, whereas late October is the appropriate planting time to obtain a higher grain yield.