were determined using FAAS; the N-NH 4 and N-NO 3 content was analysed using a SAN ++ SFA continuous flow colorimeter (Skalar Analytical B.V., Holland). The solubility index (I), presented as the percentage share of water-extractable forms of macro-and micronutrients in the total content, was calculated according to Eq. (1): p-macro-or microelement, pw-water-extractable form of element, pt-total content of the element. Statistical analysis. Results were statistically verified using Statistica 12.5. Means were compared by the Tukey test, at a confidence level of P < 0.05. Results and discussion pH and ec during composting. Changes in H + concentration were observed during composting of MSW, reflected by analysis of water solution pH (Table 1). The lowest pH values (6.9) were found for water extracts from raw material. During the composting process, the pH increased, with the highest values being observed at between 54 and 126 days. In the following phases of the composting process, a slight decrease in pH was observed (8.0-8.1), but the result was significantly higher than those observed in the first days of the composting process. The decomposition of organic matter, particularly its components like proteins, amino acids and peptides, causes the release of ammonium which contributes to an increase in pH 36. Changes in the EC of water extracts during the composting process were observed as well (Table 1). The values of this parameter depended on the length of the composting process, significantly decreasing with an increased in composting time. After about 54-70 days of composting, the EC value was about 2 mS/cm, and in the final phase it increased slightly to 2.15 mS/cm. From the 54th to 68th day of composting, we observed some stabilization of EC, and lower values with respect to that of the initial material, indicating a reduction in the amount of soluble salts in the matured compost. The results obtained, according to many authors 36,37 , suggest that the concentrations of soluble salts in the compost analysed here were in the range considered non-phytotoxic.

Soil amendments from peats, brown coals and composts produced from segregated biodegradable waste or biomass from fallow land can increase soil fertility and improve soil productivity. The aim of the study was to determine the possibility of using willow (Salix viminalis L.) biomass composts as a substrate component in horticulture. The objects of the research were composts produced from willow carried out in a pile under aerobic conditions. The addition of hay and mineral nitrogen (Nmin) was used to improve process efficiency. In order to verify the type and determine fertilizing value, basic chemical parameters were analyzed (pH, total contents of C, N and P) and a pot experiment was established to analyze the germination and growth of lettuce (Lactuca sativa L.). Changes in pH, an increase in total nitrogen content (TN), phosphorus (TP) and a decrease in TOC was observed in the investigated samples. Results of the experiment showed that the highest yield was obtained from the pots with the mixture of willow, hay and Nmin. Matured composts significantly stimulated the germination and growth of the test plants. It can be concluded that the addition of hay and Nmin significantly improved composting process and increased the fertilizing value of the investigated composts.

The aim of the study was to assess the transformation of humic substances during composting of biomass of energetic plants and municipal solid waste. The type of the organic material to be composted and the type of technology used affect the course of the humic substances transformation and formation of compost maturity parameters. Compost produced from the mixture of energetic willow and hay biomass contained humic substances with higher share of low-molecular fractions and lower share of humic acids in total organic carbon than those produced from municipal solid wastes. Obtained results also showed that insoluble alkali fraction plays an important role in humification process by its convertion to a new humic substances. Share of humic and fulvic fractions in relation to the total organic carbon appears to be reliable indicator of composting as a process of enhancing organic matter humification.

The aim of the research was to analyze the composting process with respect to changes in some physical and physicochemical properties of the organic part of municipal solid waste and willow and hay biomass mixture. The dynamics of changes in cation exchange capacity CEC values in relation to the base value of the initial materials of both tested composts were higher for municipal solid wastes compost (MSWC) compost than for willow biomass compost (WBC). The dynamics of pH changes were similar in the tested types of compost and were rather small during the process of composting, regardless of the type of organic residues and initial reaction. During composting process, the transformation of organic matter and mineral components slows down after reaching a stabilization phase.

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