А. К. Раджабов The production of planting material for fruit, forest and ornamental perennial crops has been recently characterized by a tendency to obtain and use seedlings with a root-balled system (RBS) for setting out new plantings. To obtain the best results in the cultivation of this type of planting material, it is necessary to study a sufficiently large number of parameters, including the selection of the optimal soil substrate, taking into account its composition, which will depend on chemical and physical parameters, resistance to leaching of nutrients, etc. This study was conducted in order to establish patterns of changes in the elements offertility in the soil mixture for cultivating seedlings with the RBS, evaluate the effectiveness of substrates and determine the optimal composition of the substrate for growing apple seedlings with the RBS. The authors studied some regularities of changes in the following components of soil fertility of the substrate depending on its composition: the content of organic matter, the reaction of the soil environment, the absorption capacity, the amount of absorbed bases, and the content of the main macronutrients. According to the data obtained, the use of various components in the soil composition significantly affects the elements of fertility and the dynamics of changes in their parameters during the period of growing seedlings in containers. The use of organic additives contributes to partial compensation of nutrients, due to the process of mineralization of these components. On the other hand, such substrates showed a longer mobilization of nutrients that are provided to plants. The results have shown that perlite and humus are the most effective components of soils that ensure the greatest growth of shoots of the studied plants. The maximum changes in nitrogen were observed in the variant of a sandy substrate. The content of mobile phosphorus in the composition of substrates based on peat and humus was the most stable. A significant decrease in the content of exchangeable potassium was found in the variants using perlite, ver-micompost and humus.
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