EVALUATION OF PHYSICAL, CHEMICAL, BIOCHEMICAL AND PHYTOTOXICITY OF TUNISIAN MATURE AGRICULTURAL WASTES AS COMPOSTS

In this study six final products of co-composting were evaluated by comparing the changes in physical, chemical and biochemical properties and phytotoxicity of different mature composts. These were obtained by composting agricultural wastes (almond and sesame shells, olive husk, olive mill waste water sludge, poultry manure, green and wood wastes) for eighteen months. The studied composts were character-ized by basic pH, mostly over pH 9, and an EC value ranging from 1.6 to 3.6 mS/cm. Organic matter (OM) and C/N ratio of composts ranged from 20% to 46% and 10% to 21% respectively. The biological stability of composts was evaluated by measuring cellulose, hemicelluloses, and lignin and Weende cellulose contents as well as by calculating Biological Stability Index (BSI). The BSI ranged from 0.13 to 1.31. Phytotoxicity of composts was studied by determining cress seed germination in mixtures of relative compost and peat. The variation in properties is related to the nature of used agricultural wastes. Some of these properties are compatible with using composts as components in substrates for horticultural and soilless culture: other are compatible with composts as soil fertilisers.