Influence of Foliar Application with Potassium and Magnesium on Growth, Yield and Oil Quality of “Koroneiki” Olive Trees
Background: The successful orchard management practices are directed toward obtaining a suitable yield with good fruit quality. One of the most important cultural practices is the mineral nutrition especially in the new reclaimed lands. Under sandy soil conditions the water and nutrient holding capacity is poor, so foliar application is a high efficiency to satisfy plant requirement with nutrient elements directly and quickly and economic than soil fertilizer. Although, the well known physiological roles of magnesium and potassium in plant metabolism, the number of studies addressing their significance effects on olive oil quality appears very limited. Objective: Therefore, the objective of this study was to evaluate the effects of foliar application with magnesium and potassium on growth, yield, fruit quality, physical and chemical oil properties. Materials and Methods: This study was conducted during two successive seasons 2014 and 2015 on 10 years old Koroneiki olive trees planted at 5×5 m grown in sandy soil at the experimental research station of National Research Center at El-Nobarya, El-Behera governorate Egypt. Trees were sprayed twice at final fruit set stage and 1 month later with magnesium sulphate at (0.5 and 1.5%) and potassium sulphate at (3 and 5%), besides control (spraying with water only). Results: Results indicated that the different concentrations of foliar application with magnesium and potassium sulphate especially 1.5 and 3% respectively improved the vegetative growth, fruit set, yield, fruit quality and oil content of Koroneiki olives. All samples of oils were classified as extra virgin olive oil. Free fatty acids, peroxide, iodine values, K232 and K268 significantly decreased. While, the oxidative stability significantly increased, furthermore it is higher in second season than the first season. Analysis of fatty acids composition by GC-capillary column of these oils indicated that the monounsaturated fatty acid (MUSFA) in particular oleic acid for samples which applied with magnesium and potassium sulphate was increased, whereas polyunsaturated fatty acids (PUSFA) in particular linoleic acid was decreased. The highest oleic acid content and the lowest K232 and K268 factors express the effectiveness of treatment on oil quality. Conclusion: The results of this study clearly demonstrate that spraying magnesium sulphate at 1.5% and potassium sulphate at 3% twice at final fruit set stage and one month later improving growth, yield, fruit quality and physical and chemical oil properties of Koroneiki olive. Thus, it may be recommended spray with this treatment under similar conditions.