The research aimed at comparing the yield-forming value of various sewage sludges and at determining the extent to which plants utilised nutrients (N, P, K) from the fertilisers applied. Sewage sludge was used at two dates – in autumn and in spring. As suggested by the plant yields obtained, such fertilisation was more effective when sewage sludge was applied in autumn than in spring. The yield-forming effect was stronger for municipal sludge than for industrial sludge. Irrespective of the date of fertilisation and the species or even the part of the cultivated plant, the nitrogen content of plant biomass was highest in mineral fertiliser treatments. In the same treatments plants utilised this component to the greatest extent. The amount of nitrogen utilised by plants in sewage sludge treatments (irrespective of the fertilisation date) ranged between 21.8 and 37.3%. In such treatments the nitrogen content of plants was not higher than in those fertilised with farmyard manure. The phosphorus utilisation was low and regardless of the experimental series and kind of fertiliser ranged from 8.9 to 13.9%. A larger amount of potassium was found in the biomass of plants cultivated in the spring series. Potassium was utilised to the greatest extent in farmyard manure treatments.

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