The objective of the performed investigation was to ascertain the impact of different doses of sewage sludge (2t, 4t and 8t d.m. sewage sludge·ha^-1·year^-1) on the developmental dynamics of oligotrophic, copiotrophic, cellulolytic and proteolytic microorganisms. Soil samples for microbiological analyses were collected at six dates connected with the developmental phases of spring barley. The incorporation into the soil of organic matter in the form of sewage sludge resulted in a slight increase in the counts of all the analyzed groups of microorganisms. The performed statistical analysis showed a positive correlation between the intensity of the CO₂ release and numbers of the discussed microorganisms in all fertilization treatments.