A field experiment was conducted during 2015 and 2016 seasons at the Experimental Farm, Horticulture Dept., Fac. Agric., Benha Univ. to evaluate the effect of some fertilization treatments [10, 20 and 30 m3 compost/fed + bio fertilizer (nitrobein + phosphorein + potassiumag)] when compared with the recommended dose of chemical fertilizer in the presence of micro-nutrients Fe + Mn + Zn foliar spraying (0.0, 50, 100 and 150 ppm) as well as their interaction between them on some growth parameters, yield and chemical constituents of roselle (Hibiscus sabdariffa L.) plants during 2015 and 2016 seasons.
In this respect, all applied fertilizer treatments statistically and positively affected each of plant height, number of leaves, branches and fruits/plant, fresh and dry weight of leaves, branches and sepals/plant, sepals anthocyanin and vitamin-C content, leaf N, P, K, total carbohydrates, Fe, Zn and Mn content and total indoles but they decreased the values of total phenols contents, especially T2 treatment (the recommended dose of chemical fertilizer) or 30 m3 compost/fed + bio fertilizer (nitrobein + phosphorein + potassiumag), with the exception of sepals acidity with none significant differences in the two seasons. Also, all concentrations of micro-nutrients Fe + Mn + Zn significantly improved all the aforementioned parameters, especially using the high rates. Additionally, the highest values of plant height, number of leaves and branches/plant, fresh and dry weight of leaves and branches/plant, number of fruits/plant, seed yield/plant (g), leaf N, P, K, total carbohydrates, Fe, Zn and Mn content, total indoles as well as the lowest values of total phenols contents were recorded by the combined treatment between T2 recommended dose chemical fertilizer and 150ppm Fe + Mn + Zn acid in both seasons. Moreover, the combined treatment between T5 (30 m3) compost/fed + bio fertilizer and 150 ppm Fe + Mn + Zn gave the highest values of fresh and dry weight of sepals/plant sepals acidity, sepals anthocyanin and vitamin-C content of roselle plants as compared with control in both seasons. Furthermore, the combined treatments of T4 (20 m3) compost/fed + bio fertilizer and 150 ppm Fe + Mn + Zn induced high significant increments in this concern in the two seasons.
Consequently, it is preferable to treat roselle plants with the combined treatment between T2 (recommended dose of chemical fertilizer) or T5 (30 m3) compost/fed + bio fertilizer (nitrobein + phosphorein + potassiumag) and Fe + Mn + Zn at 150 ppm for enhancing growth and productivity of this plants.