Reference values for fruit analyses at early vegetation and differences among cultivars in apple trees

Fertilizers are commonly applied to improve the yield and quality in orchards. Leaf analyses are usually used worldwide for conscious fertilization. However, there may not be linear relationships always between leaf and fruit nutrient contents. On the other hand, fruit quality problems are directly related to fruit nutrient contents. Therefore, fruit analyses assessed together with leaf analyses are more reliable in assessing nutritional status of orchards. Fruit analyses on the other hand are possible with the reference values to be established for fruits. In this study, 260 apple orchards were selected from Isparta province of Turkey in where apple is cultivated intensively. Fruit samples were taken at 6 different periods covering the timeframe from June drops to harvest and the reference values representing deficiency and excess limits for N, P, K, Ca, Mg, Fe, Mn, Zn and B in each period were determined. To determine the reference values for all sampling periods, the regression curves were created by using the reference values of each period. A decrease was observed in reference values of all nutrients with increasing number of days from the full bloom. The cultivar-induced differences were also put forth in assessment of fruit analyses. Cultivars were compared in 68 orchards composed of different cultivars grafted on seedling rootstocks and at full-yield in two districts with different soil characteristics. Cultivars were found to be significant for all nutrients, except for N, Fe, Cu and Zn and the greatest values were observed in Granny Smith.