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Soil is a highly complex system in which bacteria play a dominant role. Soil microorganism biodiversity is extremely important for sustaining the nutrient cycles of soil ecosystems. The diversity of soil bacterial and fungal communities can be influenced by agricultural management. The use of amendments, such as the incorporation of compost into the soil, strongly affects soil microbial communities directly or indirectly. The use of compost can be an important tool to control soil-borne pathogens. Certain groups of microorganisms (bacteria and fungi) present in compost produce metabolites, such as siderophores and antibiotics, with specific suppressive activity against soilborne pathogens: among these compost bacteria, species of Pseudomonas and Bacillus are very important. In this study, we investigated the effects of increasing doses of compost on the density of several cultivable soil microbial groups in an agricultural system of Southern Italy. The number of total bacteria, total fungi, siderophore-producing bacteria (principally Pseudomonas spp.) and spore-forming bacteria (principally Bacillus spp.) was evaluated over a period of five months. Moreover, we analyzed the ability of spore-forming bacteria isolated from soil and compost to inhibit, in vitro, five soil-borne phytopathogenic fungi (Rhizoctonia solani, Fusarium oxysporum, Sclerotinia minor, Fusarium solani, Pyrenochaeta lycopersici). The number of total bacteria and siderophore-producing bacteria was greater in the soil treated with compost than in soils treated with mineral fertilization or not manured, with an increase related to the dose of compost applied. Moreover, the compost used in this study produced a substantial increase in the number of spore-forming bacteria in the soil. Approximately 80% of these bacteria were able to inhibit the soil-borne phytopathogenic fungi Rhizoctonia solani, Fusarium oxysporum, Sclerotinia minor, Fusarium solani and Pyrenochaeta lycopersici. These results show that compost from the organic fraction of municipal solid wastes furnishes a high number of spore-forming bacteria exhibiting antibiotic activity against phytopathogenic fungi. The application of compost can change the composition of the soil microbial community, modifying the relationships among microorganisms, both competitive and/or antagonistic, producing a decrease in the activity of plant pathogens. These results were in agreement with the decrease in the symptoms of disease on tomato plants cultivated in the soils treated in this study.

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This study aimed to assess soil quality by chemical and ecotoxicological investigations and to check the correspondence between soil metal concentrations and ecotoxicity. For these purposes, surface soils collected at four adjacent roadside urban parks and at a former industrial area were characterized for C/N, organic matter content, texture, and pH. Cr, Cu, Ni and Pb, chosen among the most representative soil metal contaminants, were measured as total content and as available and water soluble fractions. In addition, the total concentrations of the investigated metals were used to calculate two chemical indices: the contamination and the potential ecological risk factors. The toxicity of the investigated soils was evaluated by an ecotoxicity test battery carried out on both soil samples (Vibrio fischeri, Heterocypris incongruens and Sinapis alba) and elutriates (Vibrio fischeri, Daphnia magna and Selenastrum capricornutum). The findings, both by the chemical and ecotoxicological approaches, would suggest that the soils with high metal contamination pose ecological risks. On the other hand, moderately metal contaminated soils did not exclude soil ecotoxicity. In fact, toxic effects were also highlighted in soils with low metal content, toxicity being affected by metal availability and soil characteristics. Moreover, the results suggest the importance of using a battery of tests to assess soil ecotoxicity.

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