The Effect of Sowing Date and Plant Density on Yield and Yield Components of Roselle (Hibiscus sabdariffa L.) under Jiroft Climate Conditions

Details of the mutual effect with the agronomic factors, genetic and climatic conditions should be identified to crop a plant in a new area. 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. The plant density is the most important influencing factors on the development and production of medicinal plants and is an important factor in achieving optimal performance. This research has been conducted for determination of best sowing date and intra row Roselle cultivation in Jiroft area. The objectives of the study were to evaluate the effects of plant density and sowing date on yield, yield components and some of morphological traits on Rosellee (Hibiscus sabdariffa L.) and also determine the optimum intra-row spacing and sowing date in order to obtain better yield in Jiroft environment conditions.
The field experiment was split plot in a randomized complete blocks design with three replications in agricultural research field (Long. 57°44´ E., Lat. 28°40´ N., Alt. 650 m) of Jiroft University at 2013-2014 growing season. Main plots were sowing date at five levels of 11th and 30th March, 14th April, 5th and 22th May and intra-rows were spaced of 100, 75 and 50 cm as sub plot. Each plot was 3×6 m. The spacing was 1 m between sub-plots, 2 m between main plots and replications. Traits such as plant height, the number of branches, the number of bolls per plant, boll dry weight of plant, sepal yield, seed yield, biomass yield, seed harvest index, and sepal harvest index were measured.
Plants were harvested on 1th December, 2014. An area equivalent to 2 × 3 square meters from the center of each plot was harvested by removing the effect of marginal plants from the soil surface to measure the yield of sepal and biomass. After drying the plants were weighed in open air and the shade. In addition, properties of the height, the number of bolls per plant, the number of branches per plant, sepal dry weight per plant and seed weight per plant, randomly were picked and measured by the five plants of adjacent lines of each plot middle rows. Sepal and seed harvest index, was calculated from the sepal and seed yield proportion to total biomass, respectively.
The results indicated that sowing date and intra- rows of plants had a significant effect on most of the studied traits. Delayed sowing date reduced plant height, the number of branches, the number of bolls per plant, dry boll weight per plant, sepal yield, seed yield and biomass yield. Sepal harvest index and seed harvest index were not affected by sowing date treatment. By reducing the distance between the row increased height, sepal yield, seed yield, biomass yield and the number of branches per plant, the number of bolls per plant, dry boll weight per plant, seed weight per plant and seed harvest index was decreased. The intra-row had not a significant effect on sepal harvest index. Yield of the seed and sepal in 50cm row spacing showed increment than 75 and 100 cm row spacing about 9%, 19% and 16.5%, 50%, respectively. In this study, according to long-term growth of Roselle plant, it seems that in the distance between 50 cm plant row and with doubling plant density than a distance of 100 cm, has been provided less space and food material for plant. Therefore it causes intensifying the Inter- specific competition and the number of bolls per plant, boll weight, seed weight and sepal weight per plant decreased. But increasing the number of plants per area unit led to increased seed and sepal yield.
According to the obtained results of this study can be say that the delay in sowing date led to reduce the number of bolls, dry boll and sepal weight, as well as reduction of seed and sepal yield. Reduction the distance between rows of plants from 100 to 50 cm causes to reduce the number of bolls, dry boll weight, dry sepal weight and seed weight per single plant but increased seed and sepal yield per unit area. 11th March sowing date produced the highest seed and sepal yield. However, according to the no significant increase of the sowing date relative to 30th March sowing date in order to reduce production costs, Roselle sowing date in the first half of March to mid of May with plant row spacing of 50 cm, seems to be appropriate by the good climatic conditions of Jiroft.