The results of a five-year study of the mineral fertilizers' effect on the chemical composition of Venyaminovskoe apple cultivar fruits are presented. It is shown that the use of soil and foliar application of nitrogen and potash fertilizers did not have a significant effect on the content of soluble solids, sugars, titrated acids, ascorbic acid, and phenolic compounds in fruits. It was established that the most significant factor affecting the chemical composition of fruits are the weather conditions of the growing season. At the same time, the content of ascorbic acid significantly exceeding the control over an average of five experimental years was found in the option with the introduction of nitrogen and potash fertilizers into the soil at a dose of N60K80 together with foliar top dressing. There is a tendency of increasing accumulation of leucoanthocyanins in fruits over the years. In 2021, there was a significant decrease in catechins with the use of mineral fertilizers at a dose of N60K80, as well as in the following options: without soil and minimal (N30K40) fertilization against the background of top dressing.

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The research aimed to study seasonal dynamics of content of Nmin (ammonium and nitrate forms of nitrogen) in the soil of a young sour cherry orchard as aff ected by nitrogen fertilizers. The experiment was conducted with 4-years old sour cherry trees of the ‘Turgenevka’ variety during the growing seasons of 2018 and 2019. The experimental orchard was situated at forest-steppe zone of the Central Russian Upland (Orel region) with loamy Haplic Luvisol. The treatments included: 1. Control (without fertilizers); 2. N30K40; 3. N60K80; 4. N90K120; 5. N120K160. Urea and potassium sulfate were used as fertilizers and were soil applied once a year at early spring. Soil samples were collected in soil layers from a depth of 0…20, 20…40 and 40…60 cm fi ve times during the growing seasons: in May, June, July, August and September. Without fertilizers, mineral nitrogen content varied within 3.1…31.7 mg/kg during both growing seasons. The fertilizer treatments resulted in essential rise of Nmin to 4.7…147.6 and 20.3…102.5 mg/kg in 2018 and 2019 growing seasons respectively. In both 2018 and 2019 the Nmin concentration in 0…60 cm soil layer was the highest in May…June, and decreased by 1.3-5 times in July…August. The fertilization by urea in N90 and N120 doses led to at essential increase of soil nitrogen content by 1.6-5 times compared with unfertilized soil in early summer. The movement of mineral nitrogen to the deeper soil layers was observed when applying of nitrogen fertilizers at the dose of N120. The greatest productivity of 4-years old ‘Turgenevka’ sour cherry trees was observed at N120K160 treatment (5.38 and 9.33 kg/tree in 2018 and 2019 respectively), but the increase in yield compared to the control was not statistically signifi cant.

The aim of the investigation was to research the mineral nitrogen (Nmin) behavior in loamy haplic Luvisols of orchards located in the forest-steppe zone of the Central Russian Upland. The seasonal dynamics of N min (ammonium + nitrates) was studied during the growing seasons of 2018 and 2019 in field experiments with apple and sour cherry. Fertilizers were applied annually in spring at doses increasing from N30K40 to N120K160. The most important factors influencing the nitrogen dynamics were meteorological conditions, productivity of trees, peculiarities of nitrogen uptake by the studied crops. Fertilization of orchards with nitrogen contributed to an increase in Nmin content by 1.5 … 5 times, depending on the dose. The dynamics of Nmin in the soil of fertilized and unfertilized plots was similar and depended on the biological features of the crops: the lowest indicator’s level in the soil under sour cherry was in July during fruit ripening, while in the apple orchard a low nitrogen content was noted in August. Studies have shown that in the climatic conditions of the Central Russian Uplands, loamy haplic Luvisols without additional application of nitrogen fertilizers can provide a favorable level of nitrogen nutrition for apple and sour cherry trees in the first years of fruiting.

The experiment was carried out to study the relationship between the soil calcium conditions and the content of this element in fruit and leaves of apple trees at ground fertilization with nitrogen and potassium. The experimental orchard is located in the forest-steppe zone of the Central Russian Upland (Oryol region). The soil of the orchard is Loamy haplic luvisol with a slightly acidic reaction and a high content of organic matter. Fruit plantations are represented by apple trees of ‘Sinap orlovsky’ variety on rootstock 54-118 planted in 2013. Ammonium nitrate and potassium chloride were used as soil fertilizers and applied early in spring at doses of N30K40, N60K80 and N90K120. Annually from 2016 to 2019, the content of exchangeable and water-soluble Ca compounds in the orchard soil and the total element content in leaves and fruits were determined. With the annual application of nitrogen and potash fertilizers the changes in the conditions of apple tree calcium nutrition occured already in the first years after treatments. The changes lay in increasing the calcium mobility and subsequent decrease in the element’s concentration in the root zone. At the same time, there was an annual decrease in the calcium status of fruits. The Ca content in fruits was positively correlated with the content in the soil of exchange (r = 0.43; P<0.05) and water-soluble (r = 0.51; P<0.01) forms of the element. There was no statistically significant relationship between the studied soil calcium forms and element content in apple leaves.