Response of roselle (Hibiscus sabdariffa L.) as a medicinal plant to planting date and micronutrient spraying in alley cropping

Roselle (Hibiscus sabdariffa L.) is an annual or biennial medicinal plant and belongs to the Malvaceae family, that cultivated for its stem, fiber, edible calyces, leaves and seeds. Sepals of Roselle have medicinal properties and culinary uses (MohammadpourVeshvaei et al., 2015). Cultivation of medicinal plants using sustainable agricultural system provides the best conditions for the production of these plants and leading to maximum qualitative and quantitative yield (Matinkhah et al., 2003). The purpose of sowing date determination is to find the desired planting time as environmental factors at the time that is suitable for growing, seedling and plant’s survival and resume of growth and development and the plant does not meet unfavorable conditions. For adequate plant growth and production, micronutrients are needed in small quantities; however, their deficiencies cause a great disturbance in the physiological and metabolic processes in the plant. Micronutrients, especially Fe and Zn, act either as metal components of various enzymes or as functional, structural, or regulatory cofactors (Hemantaranjan, 1996). The objectives of this research were to determine the effects of sowing date and zinc and iron spraying on growth parameters and yield of roselle in Bam in alley cropping. This experiment was conducted in 2015 in Bam under in alley cropping. The experimental design was split plot based on randomized complete block design with three replications. Sowing date including April 9 and 30 and May 20 comprising the main-treatment and micronutrient spraying including placebo (sprayed with distilled water), iron sulfate and zinc sulfate at 0.5 percentage and combination of them as sub-treatments. Micronutrient spraying was carried out at two stages of two-leaf stage and 6 to 8-leaf stage. Sepals harvested at the end of growth season. Five plants were randomly sampled from each plot and plant height, number of lateral branches, number of bolls per plant, boll weights, fresh weight of shoot, sepal yield, content of anthocyanin and protein in sepals, content organic matter, ash, potassium and phosphorus in seed were measured. Data were analyzed using SAS 9.2 statistical package. The Duncan Multiple Range Test (DMRT) at 5% level was used to compare the means of treatments. Results indicated that planting date of April 9 and zinc spraying had the greatest significant impact on plant height. Interaction of planting date and zinc and iron micronutrient spraying was significant on number of lateral branch and boll per plant, boll weight, protein percentage and anthocyanin content in sepal, sepal yield, content of organic matter and ash and concentration of potassium in seed. The greatest number of lateral branch and sepal yield and protein percentage was observed in plants sowed in April 9 and sprayed with iron plus zinc and the greatest sepal anthocyanin content, potassium content, organic matter and ash content was observed at plants sowed in April 30 and sprayed with iron plus zinc. Sowing date of April 9 due to longer growth season produced larger plants. Across micronutrient treatments, spraying of zinc by increasing the amount of growth regulators, helping metabolism of the material, and contributing to cell division of the meristem tissues increased bull number and sepal yield. The results suggested that to achieve maximum production of medicinal plant roselle planting date of April 19 to 30 along with iron plus zinc spraying would be suitable