Abstract

Roselle (Hibiscus sabdariffa L.) is an important tropical and subtropical crop, because of its multi uses in the medicinal purposes as well as food industries. A plot experiment was conducted in a Vertisol in Egypt over two sequential seasons (2013 and 2014) to assess the effect of silicon (Si) fertilization on roselle growth and yield. Specific growth characteristics measured were: plant heights, branching, and leaves; biomass and calyces yield; and concentrations of anthocyanin, total soluble solids (TSS), carbohydrates, N, P, and K in the calyces. The experiment compared five rates of Si fertilization (0.00, 1.75, 3.50, 5.25, and 7.00 kg Si ha^-1).  One-third of each rate was applied as a foliar spray at 45, 60, and 75 days after sowing, respectively. Results showed an increase in plant height, number of branches and leaves to Si fertilization rates. Similarly, anthocyanin and TSS concentration increased with increasing Si rates. Anthocyanin concentration significantly increased by 16.3% as the applied Si rate increased from 0.00 to 5.25 kg Si ha^-1. However, carbohydrate content was not affected by the applied Si rates. Nutrients (N, P, and K) concentrations, in the calyces extract, increased with increasing the applied Si rate. Biomass and calyces yield increased by 23 and 33%, respectively, as the applied Si rate increased from 0.00 to 5.25 kg Si ha^-1. The highest values of all of the measured properties were observed under the Si rate of 5.25 kg Si ha^-1, and the lowest values were obtained from the control treatment (0.00 kg Si ha^-1).

Key words: Calyces, anthocyanin, hibiscus, silicon.