Effect of Fertilizer Resources and Different Irrigation Regimes on Yield, Yield Component, Antioxidant Activity and Calyx Anthocyanin Contents of Roselle (Hibiscus sabdariffa L.) in Jiroft Area

Roselle (Hibiscus sabdarjffa L.) is an annual or biennial plant cultivated for its stem, fiber, edible calyces, leaves and seeds and belongs to the malvaceae family. Sepals of Roselle have good color and are potential source of antioxidant compounds, Studies conducted on medicinal plants in natural ecosystems suggest that using sustainable agricultural system provides the best conditions for the production of these plants, leading to maximum qualitative and quantitative yield in such conditions. Roselle is one of the plants that needs less water and is resistant to drought. It can be used as a suitable plant for cultivation in southern areas of Iran that face water scarcity.
In order to evaluate the effects of fertilizer resources and different irrigation regimes on yield, yield components, antioxidant activity and calyx anthocyanin content of Roselle (Hibiscus sabdariffa L.), an experiment was conducted at Agricultural Research Farm of Jiroft University in 2013 and 2014 growing seasons. An experiment was conducted as strip plot based on a randomized complete blocks design with three replications. Three irrigation regimes (100, 80 and 60% of crop water requirement) were assigned as horizontal factor and four fertilizer resources (mycorrhiza, vermicompost, cow manure and chemical fertilizer (NPK)) were allocated as vertical factor. Plant water requirement was calculated by AGWAT software. Then, treatments of 80 and 60 percentage of water requirement was determined and irrigation water was recorded in each irrigation period using water meter. The antioxidant activity and anthocyanin content of Roselle calyx were determined using the method described by Abe et al., (1998) and Wanger (1976), respectively. Finally, data analysis was done using SAS 12.5 and means were compared by LSD’s multiple range test at 5% level of probability.
Based on two years data combined analysis, the results indicated that fertilizer resources and irrigation levels had significant effect on plant height, Inflorescence length, number of bolls, boll dry weight, calyx yield, biomass yield, anioxidant activity and anthocyanin content. Calyx harvest index was not affected by fertilizer resources and irrigation levels. The interaction effect of fertilizer resources and irrigation regimes had a significant effect on calyx yield. The evaluation of anthocyanin value at different levels of irrigation showed that, except for in time of using vermicompost, anthocyanin value at the irrigation level of 60% was higher than irrigation levels of 100 and 80% of plant water requirement in combination with other different nutrition sources. The highest anthocyanin value was found in the control treatment when it was under moisture level of 60 percent. It has been stated that flavonoid increased under the water shortage and drought, leading to production of anthocyanin pigment. In a study conducted on Roselle, it was found that applying bio-fertilizers alone or in combination with chemical fertilizers increased carbohydrates and anthocyanin content. The highest calyx yield (1248 kg ha-1) was obtained at 100% crop water requirement 犌 manure treatment and the lowest calyx yield (510 kg ha-1) was obtained at 60% crop water requirement control treatments.
It seems that cow manure and vermicompost can have a positive impact on soil water holding capacity compared to other sources of fertilizers (mycorrhiza and chemical fertilizer) by increasing soil organic matter. Although mycorrhiza can have positive effects on plants growth, it seems that under this experiment, air temperature and low moisture holding capacity and organic matters of soil lead to a reduction in the positive effects of these soil organisms.