Evaluation the Effects of shade and Humic Acid on the Eco-Physiological Traits of Roselle (Hibiscus sabdariffa L.) under Different Irrigation Regimes

Roselle (Hibiscus sabdariffa L.) is important due to its versatility and multiple uses, ranging from food and beverages to traditional medicine and cosmetics. The field experiments were conducted at the research farm of Shahed University, and the grew under 0 and 50% shade, three irrigation regimes (2, 4 and 6 hours per week) and 4 levels of humic acid (0, 3, 6, and 12 kg/ha) through a split-split experiment based on a randomized complete blocks design with 3 replications. Measured parameters were plant height, stem diameter, number of flowering branches, sepal and capsule weight, number of fruits per plant, 1000-seed weight, plant dry weight, harvest index, fresh fruit length and diameter, inflorescence length, seed biological yield, flower protein (%), essential oil (%), anthocyanin (%), seed oil (%), and relative leaf water content. Results showed that shade treatments affected growth of roselle and significant differences in the most of above parameters were occurred. The highest means of sepal, seed and biological yields were observed in combination of unshade with 12 kg/ha humic acid application by 836, 1817 and 25710 kg/ha respectively. Results indicated that, 2 and 4 hours irrigation reduced seed yield 44 and 49% and biological yield 45 and 48% respectively. Shading caused a notable decline of essential oil (44%), anthocyanin (71%), protein (30.5%), and oil content (25%) compared to combinations of unshade and humic acid application treatment. In conclusion, this experiment demonstrated that shading and water deficiency had decreased the morphological traits and biological yield of the roselle plant, and applying humic acid in these conditions mitigated the adverse impacts of the stressors.