Green Compost Effectiveness in Improving Quality of an Agricultural Soil Co-contaminated by Antibiotics and Copper

This work aimed at investigating the effectiveness of a vegetal waste compost (green compost) in improving the quality of a degraded agricultural soil with a low organic carbon content, low microbial activity and co-contaminated by copper and an antibiotic (AB) mixture (sulfamethoxazole, ciprofloxacin and chlortetracycline). The soil was planted with Lactuca sativa L. and its growth was evaluated in presence/absence of the green compost in soil microcosms. Physico-chemical (e.g. pH, temperature, organic carbon and contaminants) parameters, microbial abundance (DAPI counts) and enzymatic activities (dehydrogenase, phosphatase and β-glucosidase) were integrated in a soil quality index (SQI). Moreover, microbial biodiversity (NGS) and possible presence of antibiotic resistance genes (qPCR) were investigated in the soil microbial community. The SQI results showed the effectiveness of the green compost in increasing soil quality and fertility. In fact, the lettuce growth (total biomass, leaf area, leaf number and root elongation) was significantly improved. Although antibiotics were inhibiting growth, the soil plant-microbiome system was partially able to counteract the negative effects of these contaminants. Moreover, the soil microbial community showed shifts in some populations under treatments with compost and lettuce. Antibiotic resistance genes (ARGs) were promoted in AB and copper presence with the highest values in the bulk soil. Interestingly, the green compost promoted not only the highest plant biomass, but also the lowest ARG values. The green compost proved to be a good solution for recycling waste, increasing the organic carbon, microbial activity and fertility of the degraded soil and limiting the spread of ARGs (unlike agro-zootechnical organic amendments, e.g. manure).