Factors determining the occurrence and number of bacteria of the genus Azotobacter in the soil environment

Bacteria belonging to the genus Azotobacter are microorganisms commonly found in various soils all over the world and capable of fixing atmospheric nitrogen. The biological nitrogen fixation (BNF) process annually supplies approximately 140–170 million tons of this element to the nitrogen cycle, which is of great importance from an ecological and practical point of view. Although the efficiency of atmospheric nitrogen fixation by Azotobacter spp. is not high and amounts to 20 mg N per 1 g of glucose used, these bacteria are sensitive to various environmental factors, including soil reaction, contents of organic matter, soil humidity or nutrient content, and their abundance in soils is small. These bacteria secrete numerous biologically active substances into the soil environment, which have a beneficial effect on the development of plants, which from the ecological point of view plays an important role in the functioning of agricultural ecosystems. An additional advantage of bacteria belonging to the genus Azotobacter, which speaks for their use in agriculture, is the ability to produce antifungal compounds and solubilization of insoluble phosphates. Research on Azotobacter spp. proves that the concentration of hydrogen ions (pH) is a significant factor which determines the presence of this group of bacteria in the soil environment. Many other soil properties have a large impact on the presence and development of this important agricultural group of bacteria.

The aim of the work was to systematize the knowledge on the known occurrence conditions and ecological relationships and interactions between environmental factors and the presence and abundance of Azotobacter bacteria in soils.