Optimal nutrient intake has an important effect on the growth and developement of fruit trees. Deficiency and toxicitiy of macro- and micronutrients is especially noticeable in intensive farming, where mineral nutrition can be a decisive factor contributing to yield size and fruit quality. With an experiment, which included fertilization with two nitrogen fertilizers KAN and calcium cyanamide (AD), as well as aplication of foliar fertilizers and biostimulators (FP), we studied the correlation between the mineral nutrition and yield, pomological value of nuts and kernel phenolics content of the walnut cultivar 'Elit'. We analysed the effects of fertilization by collective yield weighing, pomological analysis of the fruit and laboratory extraction of soluble and insoluble phenolic compounds in the kernels of each of the treatements KAN, AD, KAN + FP, AD + FP and the control (unfertilized). Due to adverse weather conditions in spring, the yields were low. The trees in the KAN + FP treatement gave the highest yield (5.1 kg/tree), a third more than the control. With the AD + FP combination, we got heavier nuts and kernels, as well as a greater width of the nuts. A three-time KAN fertilization gave the highest kernel ratio, while the AD + FP treatement had the lowest kernel ratio. The different nutrition treatements did not affect the nut shape, thickness and smoothness of the shell, seam closeness, ease of removal form shell or kernel color. The kernels contained 3.5 to 4.4 times more insoluble phenolics compared to the soluble fraction. The kernels in the control had the lowest insoluble phenolics content, which is very beneficial to our health. Considering the exceptional climatic conditions in 2018, further research is needed, as well as an inclusion of other cultivars, to provide a more reliable research outcome and confirm the effect of mineral nutrition on yield and nut quality in common walnut.
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