The Effect of Optimum Nitrogen Management and Planting Directions on Ecomorphological Characteristics, Yield and Yield Components of Roselle (Hibiscus sabdariffa L.)

Roselle (Hibiscus sabdariffa L.) is a medicinal plant and belongs to the family Malvaceae, short day plant, self-pollination, one year old or a few years old in the warm and indigenous climate of Africa. The main objective in crop management is to maximize light gain by crop canopy. Nitrogen is the first element that has a shortage in arid and semi-arid regions. Considering that agriculture in the Sistan region is associated with unfavorable environmental factors such as water shortages and nutrients in the soil, and severe 120-day winds. The aim of this research was to investigate the planting direction for determining the most suitable planting direction, optimal use of chemical fertilizers and determining their best application time for the medicinal plant of Roselle under Sistan climate conditions.

A split plot experiment was conducted in a randomized complete block design with three replications at the Research Institute of Zabol University during growing season of 2016-2017. Treatments experiment included two levels of planting directions two levels (North-South, East-West) As the main plot and the split of nitrogen fertilizer from the source of urea in four levels (1/3 per planting, 1/3 four leaf stage, 1/3 stem elongation; 1/2 post planting, 1/2 four leaf stage; 1/2 four leaf stage, 1/2 stem elongation; 1/3 four leaf stage, 1/3 stem elongation, 1/3 Flowering stage) as a subsidiary agent. Ecological parameters such as light, temperature and soil moisture at the end of flowering stage and organic matter, nitrogen and soil carbon were measured after plant harvest. The morphological characteristics were measured at the end of the growth season at the end of the complete inspection of the Sepals. Data were averaged for each sample (measured for 5 samples), with variance and mean computation. The mean test was performed using a 5% mean field test and a knowledge Duncan multiple test. Statistical data analysis was performed using SAS software version 9.1.

The results showed that the effect of planting directions and split of nitrogen fertilizer on traits stem height, stem diameter, number of lateral branch, number of boll, economical yield, sepals dry weight, harvest  index was significant. Except for the number of lateral branches, all morphological traits measured for north-south planting directions were the highest. The highest economical yield was 644 kg.ha-1 the biological yield of 9352 kg.ha-1and the harvest index of 6.39 kg.ha-1were obtained from treatment (1/3 four leaf stage, 1/3 stem elongation, 1/3 flowering stage) The results of correlation coefficients between morphological and ecological traits showed that the highest correlation (0.96) (0.91) was found between the number of flower bowls with economic performance and between stem diameter and economic performance, which was positive and very significant. Thereafter, there was the highest correlation (-0.85) between biological yield and soil organic matter (after plant harvest), which was negative and very significant.

The results showed that planting directions north-south enjoying the better of ecological agents increase the yield and sepals been in medicinal plant Roselle, Also with nitrogen fertilizer management in such a way that soil nitrogen availability is more adapted to the sensitive times of the need for Roselle, It can be used with a nitrogen split application in order to increase the yield of Roselle, Application of treatment (1/3 four leaf stage, 1/3 stem elongation, 1/3 Flowering stage), which is simultaneously with the plant's sensitive vegetative and reproductive stages is recommended. Therefore, the use of chemical fertilizers as a split, while lead to reducing consumption and increasing the efficiency of chemical fertilizers in order to achieve sustainable agriculture and environmental protection is recommended.