[Biological activity of the soils of the rice irrigation systems in the southern Ukraine].

The biological activity of soils was studied in the irrigation systems of the Southern Ukraina. Aerobic microorganisms were found to be widely distributed in all these soils. The cell number of Azotobacter and the activity of nitrogen fixation differed among various irrigation systems. Active nitrogen-fixing microbial associations were isolated from the soils; some of them were capable of fixation of 19.4 mg N per 1 g of assimilated glucose. The microbiological processes of certain irragation systems were characterized by reductive processes such as the intensive growth of sulphate reducing bacteria and the high activity of denitrification. The activities of protease, catalase and dehydrogenase differed among various soils, and were the lowest at a level of ground waters being 0.8 m. Flooding is one of ecological factors affecting the biological activity of the soils of irrigation systems.