Two field experiments were conducted to evaluate the effect of different levels of organic fertilizer (5, 10 and 15 m3 compost/fed.) when used with half dose of chemical fertilizer compare with full dose of chemical fertilizer in presence of ascorbic acid foliar spraying (0.0, 100 and 200 ppm) on some growth parameters, yield and chemical constituents of roselle (Hibiscus sabdariffa L.) plants during 2011 and 2012 seasons. Interaction effects between ascorbic acid and the used fertilization treatments on growth and productivity were studied as well.
The results showed that either treatment of half chemical fertilizer dose+15m3 compost/fed. or full chemical fertilizer dose significantly induced the highest values of plant height, number of leaves, branches and fruits /plant, leaves dry weight(g)/plant, fresh and dry weight of branches and sepals(g)/plant, seed yield(g)/plant, seed fixed oil per plant and per fed., sepals anthocyanin and vitamin-C content, leaf N, P, K, Fe, Zn and Mn uptake, leaf total carbohydrates, total sugars, total free amino acids content. Also, the applied treatment of half chemical fertilizer dose+15m3 compost/fed. and 200 ppm ascorbic acid foliar application were increased auxins, gibberellins and cytokinins content in shoots of roselle plants, but they decreased the values of abscisic acid during second season. Moreover, peroxidase, catalase and superoxide dismutase in leaf contents were decreased as well. However, the highest number of leaves, branches and fruits/plant, the heaviest leaves dry weight(g)/plant, the heaviest fresh and dry weights of sepals(g)/plant, the highest seed fixed oil content per plant and per fed., the highest sepals vitamin-C contents, the highest leaf N, K, Fe and Mn uptake, the highest values of chlorophyll a&b, carotenoids, total carbohydrates, total sugars, total free amino acids, gibberellins and cytokinins as well as the lowest values of abscisic acid, peroxidase and superoxide dismutase were recorded by half chemical fertilizer dose+15m3 compost/fed. treatment combined with 200 ppm ascorbic acid foliar application. Besides, the highest sepals anthocyanin content was recorded by the combined treatment between half chemical fertilizer dose+10m3 compost/fed. and 200 ppm ascorbic acid in both seasons. Moreover, the tallest plants, the heaviest fresh and dry weight of branches(g)/plant, the highest seed yield(g)/plant, the highest leaf P and Zn uptake and the highest leaf auxins content of roselle plants were scored by the full chemical fertilizer dose combined with 200 ppm ascorbic acid, followed by the combined treatment between half chemical fertilizer dose+15m3 compost/fed. and 200 ppm ascorbic acid in both seasons.
Consequently, it could be safely treated that roselle plants with the combined treatment between half dose of chemical fertilizer+15m3 compost/fed. and ascorbic acid at 200 ppm for enhancing growth and productivity of roselle plants.
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