Summary:

The condition for improving the properties of soil as well as the yield and quality of plants, as a result of fertilization with compost, is to use a stable and mature material. The degree of compost maturity can be evaluated, among others, basing on the content and properties of humus compounds. The aim of the research was to assess the changes in the content of ash, oxidizable total organic carbon as well as carbon of humus compounds in sewage sludge composted with a wheat straw addition. In addition, the aim of this work was to determine (basing on the obtained results) the degree of maturity of the produced compost. Mineralization of organic matter, which occurred during the composting process, resulted in lowering both the organic carbon content and the value of the C: N ratio, but increasing the ash content. Moreover, an increase in the content of carbon extracted from the compost with the mixture of 0,1 mol ∙ dm-3 Na4P2O7 + 0,1 mol ∙ dm-3 NaOH, and a decrease in the content of carbon extracted with distilled water were stated. The results of the carried out experiment indicated that the obtained compost was mature.