Protozoa are single-celled microorganisms that contain a cell nucleus (eukaryotes). The main function of protozoa is to make nutrients available to the crop by "grazing" on microorganisms (mainly bacteria).
The activity of protozoa is highly dependent on the presence of moisture in the soil. The range of action of protozoa is limited to water films and water-filled pores. Small pores can protect bacteria from grazing by protozoa.