Sewage sludges mixed with peat at a dry weight ratio of 1 : 1 were kept in PCV containers, and water losses were periodically made up during storage. The original materials and the materials stored for 1 month and 36 months were examined for pH, electrolytic conductivity, and the levels of dry matter, organic carbon, humus compound fractions, nitrogen and heavy metals (Zn, Pb, Cu, Cd). The results were compared with those for farmyard manure and peat. It was found that the dry matter content, pH value and electrolytic conductivity of the sludge-peat mixtures increased after 36-month storage, while the organic carbon content and, to a lesser degree, the total nitrogen content tended to decrease with time. As a result of the transformations of organic matter occurring in the mixtures, the amounts of soluble organic compounds systematically decreased. The proportion of carbon extracted with sodium pyrophosphate and sodium base was lower than 20% of the total organic carbon content whereas that of nonhydrolysing carbon exceeded 80%. The humus compounds in the mixtures contained more humic acids carbon than fulvic acids carbon. The level of the mobile forms of heavy metals in the sewage sludge-peat mixtures was low, which indicates that these elements occurred in the form of less bioavailable compounds.

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