The Effect of Potassium, Boron and Zinc Foliar Application on Fruit Characteristics of some Olive (Olea europaea L.) Cultivars

Olive tree (Olea europaea L.) is one of the most important fruit crops that, has a huge economic price. The plant is significant in the Mediterranean countries and Iran for table olive and oil. The nutritional requirements of olive are much lower than those of other fruit trees, but shortfall in these needs costs tree important physiological disorder. Fertilization, especially Potassium and micronutrients is a cultivation technique that strongly affects the productivity of olive trees. The amount of oil and fruit quality is effected by the correct nutrition. Leaf spraying is an important tool for correcting food deficiencies and improving the quality of the fruit of the planted olive trees under unsuitable conditions, which provides nutrients directly and as soon as possible to the branches and leaves, or fruit. Studies have shown that leaf feeding with potassium, boron and zinc can be useful for increasing the qualitative and qualities characteristics of fruit in most products, especially in arid and semi-arid regions. Thus, the present study was aimed to assessing the effect of zinc sulphate, boric acid and potassium sulphate foliar application on oil content and the qualitative and quantitative characteristics of fruit of three olive, “Caillet”, “Koroneiki” and “Mission” cultivars in unfavorable temperature conditions in Ahwaz. This study was carried out to investigate the effect of foliar spraying of Potassium, Boron and Zinc on the oil content and the qualitative characteristics of the fruit of three olive, “Caillet”, “Koroneiki” and “Mission” cultivars in the olive orchard of Shahid Chamran University in 2016. Spray treatments were included T0 (Distilled water as control),T1 (1000 mg/l boric acid + 1000 mg/l potassium sulfate + 1000 mg/l zinc sulfate) and T2 (2000 mg/l boric acid+2000 mg/l potassium sulfate +2000 mg/l zinc sulfate ) which applied on olive cultivars in four time including a week before the full bloom (the second half of March), two weeks after the full bloom (the first half of April), at pit hardening (the first half of June of the month) and at the stage of oil synthesis and accumulation (first half of July). The research was performed in a factorial experiment based on a randomized complete block design with three replications thirty fruits from each tree were harvested, then the qualitative characteristics of fruit such as fruit fresh weight, pit fresh weight, fresh weight of the pulp, pulp/pit ratio, length and diameter of fruit and pit and also, to determine the amount of nutrients in the fruit and 5dry weight of the pulp, the samples were placed an oven for 48 hours at 80°C. After drying, the dry weight of the pulp was calculated, then the samples were completely powdered with the milling machine and the Kjedahl method was used Nitrogen, from a Flame Photo Meter to measure Potassium concentration and Atomic Absorption Spectrophotometry method was used for measuring Zinc and Boron of the available in fruit. Data analysis was performed using SAS software and mean of comparison was done by Duncan's multiple range test at 5% probability level. The results indicated that the foliar spray had a significant effect on fruit fresh weight, fresh and dry weight of pulp, the ratio of Pulp/Pit weight, Oil content and amount of K, N, B and Zn of fruit, also fruit and pit dimension, but no significant difference in pit fresh weight were observed. Maximum oil content was 23.69% in Koroneiki cultivar sprayed with T1 treatment. Minimum oil content was 19.62% in Mission cultivar treated with distilled water. The highest and lowest rates in most of the studied traits were related to ‘Mission’ cultivar sprayed with T2 treatment and ‘Koroneiki’ cultivar treated with distilled water. The highest oil content was 23.69% in Koroneiki cultivar treated with T1 treatment. The highest amount of fresh weight of fruit (2.48 g) and pulp fresh weight (1.83 g) were obtained in ‘Mission’ cultivar treated with T2.It can be argued that food is responsible for activating cell division in addition to photosynthesis and organic matter transfer, Boron. Zinc and Potassium nutrients are treated trees, interfering with cell division and the synthesis of acid nucleic and increasing the formation and transfer of carbohydrates and by activating carbohydrate enzymes during fruit growth and development, improve the trait fruit. The results of this study indicated that the spraying of the leaves of olive fruit trees, especially with T2 treatment (2000 mg / L of potassium sulfate, zinc sulfate and acid-boric), had the most positive effect on the increase of fruit properties compared to other treatments ,and increased the qualitative and quantitative traits of the fruit. Also, the results indicated that the cultivar had an influence on the characteristics of the fruit and by creating appropriate environmental conditions, especially the supply of nutrients during the growth stage of the fruit. Finally, the Mission cultivar has best response to T2 treatment by spraying of potassium, zinc and boron. There were significant differences between mission cultivar treated with T2 and other cultivars on fresh fruit weight, fresh and dry weight of pulp and fruit oil percentage, as well as the concentration of nutrients in fruit. The improvement in fruit characteristics should be due to the formation of more fruits, larger fruit and more fruit weight due to the role of Zinc and Boron in cell division and prolongation of the cell and increasing the volume of intercellular space in mesocarp cells. Conversely, Koroneiki cultivar showed the least reaction to spraying. Therefore, the characteristics of fruits are different in different cultivars, and the type of cultivars and soluble concentrations are effective on the quality of yield, which implies that leaf application can be used to increase the quality of olive fruit in hot areas.