Influence of beneficial soil microorganisms and mineral fertilizers enriched with them on the flowering, fruiting, and physical and chemical parameters of the fruit of three-year-old strawberry plants in field cultivation

The excessive use of chemicals in plant production, including mineral fertilizers has a harmful effect on the morpho- and physiological state of strawberry plants, their yielding, and the physicochemical properties of the fruit and soil. Increasing the effectiveness of beneficial microorganisms, i.e. filamentous fungi, arbuscular mycorrhizal fungi (AMF) and bacteria, is an essential method of reducing the amount of fertilizers used to fertilize the soil. The aim of the study was to assess the effect of beneficial soil microorganisms (filamentous fungi and bacteria) applied alone or together with mineral fertilizers on the morpho- and physiological state of 'Marmolada' strawberry plants, their yielding, and the physico-chemical properties of the fruit. The experiment included the application of fungi (Aspergillus niger and Purpureocillium lilacinum), bacteria (Bacillus sp., Bacillus amyloliquefaciens and Paenibacillus polymyxa) alone or together with mineral fertilizers (Polifoska 6, Urea, Super Fos Dar 40). The study investigated the number of inflorescences and flowers, the intensity of the green colour of leaves, fruit yield and weight (g and %), pH, extract (°Brix), titratable acidity (g/100 g), fruit firmness (N), as well as the concentrations of macro-and microelements in the leaves of the plants. The obtained results depend on the type of fertilizer and its concentration. Strains of filamentous fungi or bacterial strains only (without fertilizer), increase the fruit yield by 60 and 35%, respectively. Reduced to 60% doses of Polifoska 6, Urea, and Super Fos Dar 40 combined with beneficial soil microorganisms influence the strawberry fruit yield more beneficially than the fertilizers applied in standard doses (100%). The mineral fertilizers enriched with soil beneficial fungi and bacteria increase the mean fruit weight by 25-30%. Both Super Fos Dar 40 enriched with bacterial strains and Polifoska 6 at 100% positively affect the physical and chemical properties of strawberry fruits. The application of reduced to 60% doses of Fos Dar 40 and Polifoska 6 enriched with beneficial bacterial strains increase the nitrogen and potassium contents in the leaves, respectively. Urea and Super Fos Dar 40 at 100% enriched with beneficial bacteria positively affect magnesium content in the leaves. Application of Polifoska 6 and NPK enriched with bacteria beneficially influences the iron content in the leaves. The calcium content in strawberry leaves decreases due to fertilization.