Effect of Foliar and Soil Fertilizers Application on the Chemical Composition of the Leaves of Plum (Prunus Domestica L.) Cv. 'Stanley'

The experiment was conducted in the period 2019-2022 in plum (Prunus domestica L.) cv. 'Stanley' plantation of the Institute of Agriculture – Kyustendil, Bulgaria. The orchard was established in 2013 with distances between trees of 5x5 m. The soil and foliar fertilizers were applied as follows: V 1 – unfertilized – (control), V 2 – Ecofol program, V 3 – Humustim, V 4 – Chicken manure Vita organic 2.5 kg/tree and V 5 – Chicken manure Vita organic 5.0 kg/tree. The influence of the fertilization treatments on the nitrogen, phosphorus and magnesium content of the plum leaves cv. 'Stanley' was non-statistically significant. The Vita organic chicken manure with a rate of 2.5 kg/tree increased the potassium content in the leaves by 15.3% above the control, and the rate of 5.0 kg/tree – by 21.0%, confirmed by the analysis, which showed statistically significant differences (P 0.001). The foliar treatment has been proven to increase the calcium content – Humustim – by 11.3% at P 0.001, and the application of the Ecofol program – by 14.3%. A positive correlation was established for the pairs nitrogen-yield – r = 0.576*, phosphorus-calcium – r = 0.564*, phosphorus-magnesium – r = 0.655* and calcium-magnesium – r = 0.683*.