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Influence of cultivar and fertilization treatment on the yield and leaf nutrients content of apple (Malus domestica Borkh.)

Fertilisation strategy can have a big impact on apple (Malus domestica Borkh) yield, with considerable environmental and economic implications. This research paper presents the yield and leaf nutrients content of three apple cultivars fertilised with three treatment regimes over 2 years (2020-202) in Bosnia and Herzegovina. The specific apple cultivars investigated were: Jonagold Decosta, Red Idared and Gala Schnitzer®Schniga, each fertilised with three treatments: T₁ (control‒without fertilization); T₂ (300 kg ha^-1 NPK (6:18:36) + 150 kg/ha N (calcium ammonium nitrate‒CAN)) and T₃ (foliar nutrition‒mixture organic-mineral fertilizer commercially named "FitoFert Kristal" (0.6%) (10:40:10) + "FitoFert Kristal" (0.6%) (20:20:20) + "FoliFetril Ca" (0.5%) (N:Ca)) in Bosnia and Herzegovina in the period of two years (2020-2021). Significant differences of different yield categories (yield per tree, yield per hectare and yield efficiency) were found among cultivar/treatment combinations, cultivars, treatments and years. Yield per tree, yield per hectare and yield efficiency were lowest in cultivar Jonagold DeCosta. Fertilization treatment T₁ significantly influenced the lowest yield per tree and yield per hectare with the magnitudes 7.55 kg tree^-1 and 27.96 t ha^-1, respectively. The highest yield efficiency was found in trees fertilised with treatment T₃ with 9.21 55 kg tree^-1, 34.11 96 t ha^-1 and yield efficiency of 0.25 kg cm^-2. Six mineral elements in the apple leaf, such as boron (B), calcium (Ca), manganese (Mn), iron (Fe), potassium (K), and zinc (Zn), were presented in known magnitudes. The cultivar Jonagold DeCosta's leaves had the highest K, B, and Zn contents with 8500.8 mg kg^-1 FW (i.e. fresh weight of leaves), 33.8 mg kg^-1 FW, and 12.2 mg kg^-1 FW, respectively, while cultivar Red Idared's leaves had the highest Ca, Fe, and Mg contents. The fertilisation treatment T₃ influenced significantly the highest content of Ca (301.37 mg kg^-1 FW), Fe (116.5 mg kg^-1 FW), B (41.6 mg kg^-1 FW), Mn (22.4 mg kg^-1 FW), and Zn (14.9 mg kg^-1 FW) in leaves, while the highest content of K was found in leaves from trees fertilised with treatment T₂ (8130.5 mg kg^-1 FW). The experimental outcomes have proven that the cultivar/treatment combinations, cultivars, treatments, and time duration (in years) are the key factors affecting the potassium, calcium, iron, boron, and manganese contents. It was concluded that the foliar application enables easier mobility of elements, which results in a greater number of fruits and larger fruits, which leads to a higher yield. This study is the first of its kind in Bosnia and Herzegovina, and the findings of this research will pave the way for future research activities involving increasing the number of cultivars and different fertilisation treatments on apple yield and leaf mineral composition.