Effect of Nitrogen Level and Natural Zeolite on Qualitative and Quantitative Function of Stevia rebaudiana (Bertoni) in Ahvaz Climatic Condition

Nowadays due to population growth and higher levels of welfare, one of the main social problems is providing appropriate food resources. In this regard, finding the alternative food resources, improvement of existing technologies and providing new technologies seem inevitable. Although sugar is a very important substance and has special place in household’s basket and economy, the harmful effects of excessive consumption of sugar should not be neglected. Stevia is a plant with a widespread root system which has a couple of years lifetime. The stems of Stevia are brittle and small and produce elliptical leaves. At first the leaves will be dried and then they will be powdered or wetted in the water and will be used for sweetening of beverages, sweet drinks, chewing gums, chocolates, cakes, etc. Stevia is one of 950 genera belonging to the family of Asteraceae plant. Stevia leaves are used for sweetening foods. Sweetness of Stevia comes from the d. terpenoides glycosides that exist in different parts of the plant. Glycosides are the result of secondary metabolism in the plants. In different components of the Stevia body, there are about 10 major glycoside compositions which the steviozede and Rbadiozide glycosides have more importance in sweetening property of Stevia compared to other sweet glycosides. Nitrogen is considered as one of the key elements in the nutrition of crops and the most important element in limiting the plant growth. Due to increased cation exchange capacity and a high tendency to absorb and retain ammonium, use of clinoptilolite on agricultural lands can have an effective role in reduction of nutrient washing especially nitrogen from soil.
In order to investigate the effect of different levels of nitrogen and natural zeolite on qualitative and quantitative yield of Stevia in Ahvaz climate, a trial agricultural research field was selected at the farm of agricultural and natural resources of Ramin Khuzestan in 2012-2013. A split plot experiment in a randomized complete block design with 3 replications was conducted. The levels of nitrogen fertilizer (50, 100, 150 and 200 N kg /ha) were applied in the main plots and based on similar studies, the levels of zeolite (including zero, 3 and 6 tons per hectare) were applied in subsidiary plots. Transplants were cultured in 2013/3/6. Harvest was done after growth and development of plant in 2013/6/10. In order to determine the performance of harvested plants from each plot, after packaging and label-making, the samples were weighted in order to estimate the wet weight. The samples were dried in an oven at 72 °C for 48 hours and reweighted again, and then the dried matter performance was determined. To measure the percentage of steviozide, leaf samples were collected from each plot and dried in an oven at 70 °C for 48 hours, then they were milled, powdered and half a gram of Stevia leaves powder in 50 ml of 70% ethanol was obtained from each sample plot. The Stevia leaf steviozide percentage was measured using a HPLC device. Before the analysis the device was calibrated.
Results showed that the highest biological performance (2253 kg ha-1), the highest leaf performance (1426 kg ha-1), the maximum stem diameter (1.66 cm), the maximum height (69 cm) and the maximum leaf area index (4.88) were obtained at the treatment of 200 kg nitrogen per hectare and the largest number of branches per plant was obtained in the 150 N kg /ha-1 treated with the use of 6 tons zeolite. Maximum percentage of steviozede (10.67) was related to 150 kg pure nitrogen per hectare with 3 tons of zeolite. LAI as a minor component of plant growth was affected directly by nitrogen fertilizer, by increasing the fertilizer, growth and leaf area of plant per square meter will be added. Leaves of the plant that consist the most part of the plant, were influenced by nitrogen fertilizer, with increasing nitrogen, growth and performance of leaves were also increased. The zeolites reduced the amount of nitrogen leaching in the soil due to frequent watering that plant needs. As a result, the plant uses nitrogen and other elements that all are useful in the vegetative growth, effectively. According to the results, interaction effect of nitrogen fertilizer and zeolite levels on the SPAD reading was significant at one percent level. The presence of nitrogen in chlorophyll causes the significant effect of increasing nitrogen fertilizer on chlorophyll content of leaves. Existence of chlorophyll as a light absorbent and synthesis of materials is vital for plant growth. The use of zeolites increases the soil cation exchange capacity and consequently the efficiency of nitrogen fertilizer in the soil. So the plant can use fertilizers better and subsequently vegetative growth increases. According to the results, there is a close relationship between supplying food components and accumulation of glycosides steviol in Stevia.
Stevia is a plant with few years life with several times harvesting each year. This plant was cultivated in 2013/3/6 and harvested in 2013/6/10. Results showed although Stevia was planted for the first time in the study area it had consistency with the regional climate. Use of nitrogen fertilizer and zeolite had a significant effect on chlorophyll components and biological performance of leaves and also on morphological characteristics of plant and nitrogen fertilizer. The zeolites increased cation exchange capacity of the soil which enhanced the efficiency of nitrogen fertilizer in the soil and resulting in the better usage of fertilizers by the plants and increasing the vegetative growth (biological and leaf yield) and percentage of steviozede.