Impact of Fulvic Acid and Stimulant Substances on Growth and Productivity of Roselle (Hibiscus Sabdariffa L.) Plant

Abstract

      A field experiment was conducted during the 2023 and 2024 seasons at the Experimental Farm, Faculty of Agriculture, Al-Azhar University, Assiut, Egypt (27°12'16.67" N, 31°09'36.86" E), to investigate the effects of fulvic acid (FA) application methods and stimulant substances on roselle (Hibiscus sabdariffa L. cv. Sabhia 17, dark line) growth, yield, and chemical composition. FA treatments included soil addition (1 and 2 g/l water), foliar spray (500 and 1000 ppm), and combined applications (1 g/l soil addition + 500 ppm foliar spray and 2 g/l soil addition + 1000 ppm foliar spray). Stimulant substances comprised chitosan (250 and 500 ppm), vitamin E (50 and 100 ppm), garlic extract (10 and 20 ml/l water), and a control (no stimulant substances). The combined treatment of 2 g/l FA soil addition with 1000 ppm foliar spray was the most effective in enhancing vegetative growth (branch number, herb dry weight), yield components (sepal and seed yields), and chemical constituents (fixed oil production, anthocyanin and acidity), outperforming the control, which showed the lowest values. Foliar application of chitosan, vitamin E, and garlic extract at all concentrations also significantly improved these parameters, with garlic extract at 20 ml/l yielding the highest results. The interaction of 2 g/l FA soil addition + 1000 ppm foliar spray with 20 ml/l garlic extract was the most effective, highlighting the potential of FA and garlic extract as sustainable, eco-friendly practices for enhancing the productivity of roselle plants. Conclusion: The combined treatment of 2 g/l FA soil addition with 1000 ppm foliar spray was the most effective in enhancing vegetative growth (branch number, herb dry weight), yield components (sepal and seed yields), and chemical constituents (fixed oil production, anthocyanin and acidity).