Assessing the impact of plant-based amendments from aromatic plants on soil fertility and microbial diversity

Sustainable agriculture is gaining increasing attention as a response to the environmental challenges posed by conventional farming systems. In this context, circular economy approaches offer promising solutions by transforming agricultural by-products into valuable resources. The processing of medicinal and aromatic plants (MAPs) generates residual biomass, known as exhausted herbs (EHs), which may serve as a sustainable organic amendment for soils. This project explores the potential of EHs to improve soil fertility and influence soil microbial community shifts. A key focus is to understand how EHs application affects the recruitment of root-associated microbial consortia that support plant growth, nutrient uptake, stress tolerance and pathogen resistance. A two-year field experiment was conducted in collaboration with a farmer cultivating MAPs and traditional maize varieties in Northern Italy. EH-based amendments were applied annually after the characterization of raw material, and soil and root samples were collected at the beginning and end of each maize growing season. To date, physical-chemical analyses and DNA extractions have been completed on 150 soil samples and 85 root samples. Ongoing and upcoming activities include morphological assessment of mycorrhization rate, high-throughput DNA sequencing (metabarcoding), and bioinformatic analyses to profile potential microbial community shifts. Additionally, a greenhouse trial is being planned to further investigate the influence of EHs under controlled conditions, offering deeper insights into the effects on soil microbiota dynamics and the potential agronomic benefits.