A pot experiment was aimed to determine changes in some chemical properties of soil after the application of sewage sludge as a fertiliser. The sludges used in the experiment came from a chemical plant treating tannery sewage and two mechanical-biological plants treating municipal sewage. It was found that the soil fertilised with sludge had a significantly higher reaction at a lower acidity than the soil receiving mineral salts and farmyard manure. The organic carbon content of soil depended more on the kind of fertiliser than the time of its application (spring vs. autumn), the results, however, were not complety clear. Sewage sludge caused a significant increase in the total nitrogen content of soil. After two years of investigations the level of bioavailable phosphorus and potassium decreased sharply in the soil of all experimental treatments.

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