The aim of the study was to determine the influence of PRP SOL and PRP EBV fertilisers and co-inoculation (simultaneous inoculation of plants with bacteria of the Rhizobium genus and endophytic Bacillus subtilis bacteria) on nitrogenase activity, the dynamics of growth of selected soil microorganisms, variation in soil biochemical properties, and soil fertility index in a yellow lupine plantation. There were 12 variants of the field experiment: 1) the control variant of uninoculated yellow lupine, 2) seeds inoculated with the Bacillus subtilis strain, 3) seeds inoculated with nitragin, 4) PRP SOL fertiliser, 5) PRP EBV fertiliser, 6) PRP SOL + PRP EBV, 7) PRP SOL fertiliser + Bacillus subtilis inoculation, 8) PRP SOL fertiliser + nitragin, 9) PRP SOL fertiliser + Bacillus subtilis + nitragin, 10) PRP EBV fertiliser + Bacillus subtilis, 11) PRP EBV fertiliser + Bacillus subtilis + nitragin, and 12) PRP SOL + PRP EBV + Bacillus subtilis + nitragin. Soil samples for microbiological and biochemical analyses were collected at 3 terms: during the emergence of plants, at the beginning of their florescence, and after harvesting. The count of selected groups of soil microorganisms (total bacterial count, moulds, Actinobacteria, copiotrophic and oligotrophic microorganisms) was measured with the serial dilution method developed by Koch. The analysis of soil enzymatic activity such as dehydrogenases and phosphatases in different variants was based on the colorimetric method, and catalase activity was measured with the manometric method. The two-year field experiment was conducted in 2014 and 2015. It showed that PRP SOL and PRP EBV fertilisers and co-inoculation applied to the yellow lupine plantation stimulated nitrogenase activity, the dynamics of growth of selected groups of soil microorganisms, variation in biochemical activity, and soil fertility index.