In order to study the effect of sowing date and plant density on yield and yield components of roselle, a split-plot experiment was carried out in the research field of Islamic Azad University, Birjand Branch, Birjan, Iran in 2008 based on a randomized complete block design with three replications. The main plot was sowing date at three levels of May 4, May 25 and June 14 and the sub-plot was plant density at four levels of 6.7, 8, 10 and 13.3 plants/m2. The results showed that the delay in sowing from May 4 to June 14 decreased fruit number per plant significantly, fruit number per m2, sepal yield per unit area, sepal dry yield and single-plant biomass by 43.6, 39.5, 44.9, 45.7 and 47.3%, respectively. As the density was increased from 8 to 13.3 plants/m2, fruit number per plant, sepal yield per fruit and plant and single-biomass decreased significantly by 29.8, 24.4, 39.1, 55.4 and 33.6%, respectively, but fruit number/m2 increased by 18.2%. The interaction between sowing date and plant density significantly affected only fruit number per plant and sepal dry yield per plant. Given the results of this study, the treatment of sowing date of May 4 with the density of 8 plants/m2had the highest sepal dry yield with an average amount of 395.33 kg/ha; and so, it is recommended for the cultivation of roselle in Birjand, Iran.
Key words: Roselle, sowing date, plant density, yield, yield components.
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