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The purpose of this study is to investigate the microbial activity and the number of different groups of microorganisms in the soil under organic agricultural systems.A range of analyses was conducted on soil samples taken from calcareous chernozem soils managed under organic (7 sites) and conventional agricultural systems (1 site). Laboratory measurements were performed in the Laboratory of Microbiology, Faculty of Agriculture, Novi Sad. The total number of bacteria, actinomycetes, fungi, aminoheterotrophs and azotobacters was determined using the dilution method. Soil dehydrogenase activity was measured spectrophotometrically.The greatest number of the Azotobacter sp. bacteria was recorded in the soil devoted to pumpkins (132.61 × 10 2 ) and in the soil devoted to apples (126.39 × 10 2 ). The greatest number of aminoheterotrophs (1786.05 x10 6 ) and the total number of bacteria (1370.82 x 10 6 ) and actinomycetes (235.45 × 10 4 ) were determined in the soil devoted to carrots. Fungi were more abounded in the soil devoted to chard (36.82 ×10 4 ) than in the soil devoted to other plants. The research results show that the soil devoted to wheat in organic production indicated a greater number of aminoheterotrophs, total bacteria, actinomycetes and fungi, whereas only the number of Azotobacter sp. was greater in the soil devoted to wheat in the conventional agricultural system. The highest dehydrogenase activity level was determined in the soil devoted to radishes, whereas the lowest dehydrogenase activity level was determined in the soil devoted to apples.

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