Effects of sowing date and planting-row spacing on agronomic traits and yield of roselle in purple soil area

To investigate the effects of different sowing dates and planting-row spacing on the agronomic traits, yield and yield components of roselle in purple soil areas, so as to provide theoretical and technical support for the high-yield of roselle cultivation in Hengyang area.Two intercropping modes（peach forest/roselle intercropping and citrus forest/roselle intercropping）were set up with roselle as the experimental material, three sowing dates（April 5, April 20 and May 5）were taken as the main plots, and three planting-row spacing（1 m×1 m, 1 m×1.5 m and 1.5 m×2 m）as the subplots, indicators such as plant height, crown width, sepal yield and its components were determined. The results showed that under the same planting-row spacing, with the delay of sowing date, the plant height and crown width of roselle intercropped under peach forest increased significantly, while those of roselle intercropped under citrus forest showed a trend of first decreasing and then increasing; both intercropping modes reached the maximum values at the sowing date of May 5. For peach forest/roselle intercropping, the 1000-seed weight decreased, while the fresh weight per sepal, fresh sepal weight per plant, fresh fruit yield per plant, fruit number per plant, dry sepal weight per plant and dry sepal yield showed an increasing trend or a trend of first increasing and then decreasing; the dry sepal yield peaked at 14217.55 kg·hm⁻² on April 20. For citrus forest/roselle intercropping, the 1000-seed weight first increased and then decreased, while the fresh sepal weight per plant, fresh fruit yield per plant, fruit number per plant, dry sepal weight per plant and dry sepal yield first decreased and then increased; the dry sepal yield reached the maximum on May 5. At the same sowing date, as the planting-row spacing increased from 1 m×1 m to 1.5 m×2 m, the plant height of roselle decreased significantly and the fresh weight per sepal increased significantly in both intercropping modes; the crown width, fresh sepal weight per plant and fresh fruit weight per plant basically showed an increasing trend or a trend of first increasing and then decreasing. Under peach forest/roselle intercropping, the fruit number per plant, 1000-seed weight and dry sepal weight per plant increased, whereas the dry sepal yield decreased. Under citrus forest/roselle intercropping, the fruit number per plant and dry sepal yield decreased, and the dry sepal weight per plant showed a decreasing trend or a trend of first increasing and then decreasing. The dry sepal yield of both intercropping modes was the best at the planting-row spacing of 1 m×1 m. Exploring the suitable sowing date and rational planting-row spacing of roselle in Hengyang can improve space utilization and increase roselle yield. The optimal combination for intercropping roselle under forests in Hengyang is sowing on April 20 with a planting-row spacing of 1m×1 m, which results in excellent agronomic traits and high dry sepal yield of roselle. The sowing date can be appropriately delayed to May 5 in case of poor soil fertility or concentrated rainy seasons.