The aim of the study was to investigate the composition of different organic substances and the amount of nutrients in composts produced from green waste, food waste, sewage sludge, cattle manure and digestate as well as to assess the contamination with persistent organic pollutants and heavy metals. Composts produced in 2015 and 2016 in different regions of Lithuania and in different weather conditions were used for the research. Chemical analyses of composts were done according to the international standards and requirements for soil improvement substances. Of all the composts tested, green waste compost had the lowest content of organic matter, nitrogen and phosphorus. The results of the experiment suggest that digestate, which was characterised by the highest organic matter content, contained the smallest quantity of fulvic and humic acids that are of key importance to the recovery of soil organic content. It was established that sewage sludge composts were the most contaminated with heavy metals and polychlorbiphenyls; the content of the analysed polychlorbiphenyls totalled 37.8 µg kg-1 in the samples of the year 2015 and 29.4 µg kg-1 in the samples of 2016. The lowest content of heavy metals and polychlorbiphenyls was recorded in cattle manure and food waste composts. No polychlorbiphenyls were found in the samples of 2015. The findings suggest that sewage sludge compost is the least suitable for being used in agriculture, because of its pollution with heavy metals and persistent organic pollutants. Green waste compost only increased the quantity of organic matter, while compost from cattle manure, food waste and digestate not only improved the soil structure, but significantly increased nutrients concentration.

Pot trial experiments were conducted with the aim of determining organic matter composition and the influence on the growth of spring barley of different types of composts. The plants were grown in 6 l vegetative pots on the experimental site of the LRCAF Agrochemical Research Laboratory. Compost with soil were mixed by the following volume – 10, 20, 30 and 40%. Spring barley was grown for two years – in 2015 and 2016. This experiment investigated green waste and food waste, sewage sludge and biogas production waste. The largest amounts of organic matter, organic and total carbon, and total nitrogen were found in the biogas production waste compost. The minimum contents of organic matter and other nutrients were estimated in the green waste compost. The following biometric measurements on spring barley were taken: plant height, 1 000 grain weight and grain yield. The best growth of barley was in the substrate with biogas production waste in 2015 – plant height 43.7–53.7 cm, 1 000 grain weight 45.6–49.2 g, grain yield per pot 19.1–23.0 g, and the minimum contents were in the green waste substrate. In 2016, the best results were obtained in the substrates with green and food waste compost. The nitrogen content was determined in spring barley grain and straw. In 2015, the total nitrogen content in plant grains and straw was increased by the substrate of biogas production waste, and in 2016 it was increased by the substrate of food waste, sewage sludge and biogas production waste.