The Effect of Newly Developed Microbial Biopreparations on the Chemical Composition of Strawberry (Fragaria × ananassa Duch.) Fruit Grown in an Organic Farming System

Non-chemical methods of fertilisation and protection have been gaining importance in recent years. This trend is closely linked to current European Union (EU) agricultural policy and the growing consumer awareness of the impact of nutrition on health. Newly developed biopreparations have to be tested for their agricultural efficiency alongside a quality assessment of the resulting food. The aim of this study was to determine whether the use of newly developed microbially enriched fertilisers in organic strawberry cultivation had an effect on fruit chemical composition and heavy metal accumulation. In the research, five biopreparations (K2–K6 combinations) containing selected Bacillus strains and plant extracts were tested in 2021 and 2022 on three strawberry cultivars: ‘Honeoye’, ‘Rumba’, and ‘Vibrant’. After the vegetation period, the collected fruit samples were frozen, freeze-dried, and subjected to chemical analyses to determine the total carbon and nitrogen content, as well as the concentration of microelements (Mn, Fe), macroelements (Na, Mg, K, Ca, P) and heavy metals (Cd, Pb, Cu, and Zn). The application of the tested biopreparations did not significantly impact the total carbon content of strawberry fruit. For most of the tested traits, cultivars reacted differently to the tested preparations. A higher total nitrogen content was found for treatments treated with biopreparations, especially for the ‘Vibrant’ cultivar—ranging from 15.2 g·kg−1 K2 (BacilRoots) to 16.3 g·kg−1 K3 (BacilRoots + BacilExtra) and K5 (BacilRoots + BacilExtra + BacilHumus)—being about 10–18% higher than on the control object (K1). The content of sodium, phosphorus, calcium, and magnesium did not change significantly under the influence of biopreparations. The use of the K3 and K5 treatment resulted in significantly lower iron contents when compared to those of the control (strawberries sprayed with water with no biopreparations added)—respectively, by 16.1% and 17.9%. ‘Vibrant’ treated with water (control treatment) showed the highest contents of iron, copper, and zinc when compared to those treated with biopreparations. No exceedances of the permissible heavy metal content were found in the samples tested.