Abstract
Pot experiment was run out to study the impacts of different nitrogen sources on microbial biomass (C and N) and other soil biological properties in Kovarvany brown forest and meadow chernozem soil types incubated at temperature 25±3°C. Pots were filled up with soil amended with sewage sludge at the levels of 0, 12.5, 25, or 50% (w/w) in comparison with soil amended with ammonium nitrate at 0, 11.5, 23 and 46 mg/kg soil for eight weeks. The results were compared with a pot containing a combination between ammonium nitrate at 23 mg/kg soil mixed with 25% of sewage sludge and with untreated control. Soil aerobic heterotroph bacterial enumeration, fungal population, soil basal respiration, total soil organic carbon, dehydrogenase and fluorescein diacetic acid (FAD) potential activities were investigated. Results indicated that the addition of sludge or NH 4 NO 3 caused changes in the sizes of microbial population which increased significantly with the increases of the application rates of organic N source (sewage sludge) more than the inorganic N source (NH 4 NO 3 ). In addition, sewage sludge had a stimulatory effect on the soil enzymatic potential activity and increases the total organic carbon. The highest number of fungi observed in meadow chernozem soil even treated with NH 4 NO 3 . It was found that Kovarvany brown forest soil had lower soil biomass and biological properties when treated with NH 4 NO 3 . Moreover, meadow chernozem soil had higher biological properties when treated with sewage sludge than NH 4 NO 3 over the Kovarvany brown forest soil. These results suggest that the positive correlation between organic fertilizer amendment and soil quality where enhance both microbial and enzymatic activities. However, the results indicated that soil enzyme activities have been proposed as appropriate indicators because of their intimate relationship to soil biology, ease of measurements, and rapid response to a small change in soil management.
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