Plant fertility and soil quality are determined by many environmental factors. Good quality crops occur when plants are grown with optimal development, nutrition and formation of crop structural elements. With the intensification of agricultural production, the use of plant protection products and mineral fertilizers is increasing. This has led to a decrease in the humus content of the soil and to a deterioration of soil quality. One of the most effective measures to maintain soil fertility is fertilization with organic fertilizers. Recently, with the declining use of organic fertilizers, a partial solution to the problem may be fertilizers enriched with humus, amino acids, seaweed extracts and other plant nutrition activators. Microbiological products strengthen the root system, accelerate the process of photosynthesis, strengthen the plant's immune system, increase resistance to adverse environmental factors and improve soil structure. Rising prices of energy resources and the EU ecological policy goals are forcing farmers to seek solutions to reduce production costs and energy resources. At the same time, new and efficient measures are sought to increase soil fertility and quality.

The investigations were carried out at the Experimental Station of Vytautas Magnus University Agriculture Academy, Lithuania, in 2019–2020, in Calc(ar)i-Endohypogleyic Luvisol, a semi-neutral (pH_KCl 6.9), high phosphorus (232.6 mg kg^-1 P₂O₅), mid-potassium-level (111.0 mg kg^-1 K₂O), mid-humus-level (2.39%) soil, in order to evaluate the effect of biological preparations on winter wheat crop. Treatments of the experiment: Factor A – biological preparations: 1) without spraying, 2) complex of fulvic and humic acids with microorganisms (biological preparation A) was sprayed (norm 1.0 L ha^-1) in autumn, 3) complex of industrial biological waste (molasses) with microorganisms (biological preparation B) was sprayed (norm 2.0 L ha^-1) in autumn. Factor B - nitrogen rates: 1) fertilized with N₁₀₅, 2) fertilized with N₁₆₅.

Available phosphorus content was significantly higher in the soil where was applied biological preparation B at both levels of nitrogen fertilization. Biological preparation A increased available potassium content in the soil where the higher amount of nitrogen rate was used compared with the control. The use of biological preparations did not have a significant effect on the germination of winter wheat but tended to promote the tillering of winter wheat and increase the number of productive stems. The use of biological preparations tended to increase the assimilation area of winter wheat leaves, the weight of 1000 grains, quantity of grain per spike, mass of grain per spike and significantly (P≤0.05) increased winter wheat yield to compare with the control. Application of biological preparations significantly (P≤0.05) increased the decomposition of winter wheat straw.