Revalorization of distillation residues of medicinal plants as soil amendments: impacts on soil health and microbiota

The increasing interest in sustainable agriculture has been driven by growing awareness of the environmental impacts of conventional farming practices. Adopting technological innovations and circular economy practices in waste management can significantly enhance efficiency and reduce ecological footprint of practices such as improper disposal. Medicinal and aromatic plants (MAPs) are rich in essential oils and usually undergo distillation processes, generating residual biomasses that should be considered valuable resources since they are still rich in bioactive compounds. This work aims to explore the valorization of these residues as soil amendments and to evaluate their effects on soil health and crops and the impacts on the assembly of microbial communities. Two experiments have been planned. A two-years open-field trial has been carried out, adding characterized MAP residues as soil amendments in a maize field in both years. Soil and root samples, delivered twice a year, have undergone DNA extraction, sequencing and metabarcoding analysis for characterizing fungal, prokaryotic and arbuscular mycorrhizal fungi (AMF) communities. Prokaryotic communities show a clearer differentiation among treatments than fungi, suggesting greater sensitivity to soil management. Results indicate that multi-year management is needed for community restructuring. A greenhouse experiment is ongoing for evaluating the effects of partial replacement of peat with mint distillation residues, combined with AMF inoculation, on growth and quality of MAP species. Physical-chemical analyses of soils have been performed in both experiments, showing significant differences among different conditions.