To enhance yield and produce high-quality olive products, it is crucial to implement accurate and balanced fertilization programs. Like other crops, olive trees require the application of specific macro and micronutrients in addition to basic fertilization. This study aimed to evaluate the effects of foliar fertilizer applications containing K as well as N, K, Ca, and B, in addition to basic fertilization, on the yield and quality parameters of the Gemlik olive (Olea europaea L. cv. Gemlik) variety, known for its high economic value and use in black table olives and oil production, during two consecutive seasons in 2021–2022. The research evaluated the effects on olive fruit yield, fruit nutrient content (N, Ca, P, Na, K, Mg, Zn, Fe, Cu, and Mn), oil yield, and quality. In addition to traditional basic fertilization (NPK fertilizer), foliar fertilizers containing K as well as N, K, Ca, and B nutrients were applied before flowering and after fruit set. These applications were organized using a randomized block design with three replicates, each consisting of three trees. The results showed that foliar fertilizer applications, in addition to basic fertilization, had a significant impact on the yield and quality parameters. Specifically, foliar K applications positively affected olive yield in the second year. Moreover, foliar fertilizer applications improved the fruit nutrient content, oil quality (K-232, K-270, peroxide, acidity, and total phenol), and oil composition (%). Therefore, it is recommended that foliar fertilizers are applied during similar periods under similar conditions. However, ensuring the continuity of an optimal fertilization management plan is crucial for olive, as it is a perennial plant.

This study was conducted to determine the nutritional status of olive cultivated land and olive plant in Izmir and Mugla province in terms of boron and other elements. For this purpose, 254 soil samples (0-30 cm depth) and 254 leaf samples were taken simultaneously with GPS coordinates from the olive production areas and analyzed (125 gardens in Datca, Koycegiz, Milas, Ula, Seydikemer districts of Mugla province / 129 gardens in Aliaga, Bayindir, Bergama, Dikili, Foca, Karaburun, Kemalpasa, Menderes, Menemen, Odemiş, Seferihisar, Selcuk, Tire, Torbali and Urla district of Izmir province). In the soil samples texture, pH, EC, lime, organic matter, extractable boron, iron, copper, zinc and manganese analysis were done. In the leaf samples total boron, iron, copper, zinc and manganese content were determined. According to the analysis results, the nutritional studies of olive were determined in term of boron and other elements. According to the results of the research, boron contents of the research areas soils ranged between 0.20 and 5.24 mg kg-1 and the average level was determined as 1.21 mg kg-1. In the boron content distribution of the soils in the research area 13.78% is low, 76.38% is sufficient, 9.45% is more and 0.39% is too high. Boron contents of olive leaves ranged between 8.66 and 29.33 mg kg-1 and the average level was determined as 8.66 mg kg-1. In the boron content distribution of the leaves in the research area 85.04% is low, 14.96% is sufficient. Based on the B contents of all soil and leaf samples it was interesting to note that although 85.83% of the soils have sufficient boron, 85.04% of the leaves show boron deficiency, indicating that boron nutritional problems are experienced. Also according to the results of analysis, it was determined that there were no nutritional problems in terms of iron, and that there were serious nutritional problems in terms of boron and zinc. It was determined that nutritional problems in term of manganese and copper slightly. As with all plant species, fertilization programs for olive plant should be established according to soil and leaf analysis result. According to the results of analysis, it is important to give the deficient macro and micronutrients in addition to phosphorus, nitrogen and potassium fertilizers which will be given with basic fertilization.