Evaluation of Yield, Harvest Index, and Water Use Efficiency of Roselle (Hibiscus sabdariffa L.) in Different Treatments of Irrigation and Sowing Date

In order to evaluate different irrigation regimes and planting date on yield, water use efficiency, and harvest index of Roselle (Hibiscus sabdarjffa L.), an experiment was conducted in form of split plot in randomized complete blocks with three replications in Karaj in 2017. Experimental treatments included irrigation round (Irrigation intervals of 8, 10, and 12 days) as a main plot, andplanting date treatments at three levels of 4th June, 18th June, and 2th July as a sub-plot. Results showed that the main effect of irrigation treatments was significant on all traits except harvest index. Planting date had a significant effect only on plant height, stem diameter, biological yield, flower water use efficiency, and sepal water use efficiency. The interaction of irrigation treatment levels and planting date only made a significant difference in biomass water use efficiency. Also, the flower harvest index was not affected by any of the applied treatments.The greatest plant height (181.2 cm), stem diameter (2.91 cm) and biological yield (14.6 t.ha-1) were obtained in the irrigation interval of 8 days. The highest sepal water use efficiency of (0.18 g.L-1), flower water use efficiency (0.034 g.L-1) and sepal harvest index (11.12 %) were observed in the irrigation interval of 12 days. The irrigation interval of 10 days had the highest sepal yield (1.59 t.ha-1) and flower yield (307.7 kg.ha-1).Delay in planting caused a decrease of 12, 16, and 7% in plant height, stem diameter, and biological yield, respectively and increase in the sepal water use efficiency and biological yield water use efficiency by 22 and 20%, respectively compared to optimum planting time. The highest biological yield water use efficiency (2.41 g.L-1) was obtained in irrigation interval of 12 days and one month delay in planting. Based on the obtained results, irrigation interval of 10 days is recommended to achieve maximum flower yield and sepal yield, increase the flower water use efficiency and sepal harvest index. Also, in order to shorten the cultivation period and save water consumption, the date of 18th June is recommended for plant cultivation in Karaj.