Valorisation of medicinal and aromatic plant residues for soil amendment purposes

Abstract Ineffective management of agricultural residues poses serious environmental challenges. In this context, the transformation of agricultural biomass into value-added products has become increasingly important. Agricultural reuse of medicinal and aromatic plant residues and their metabolites may be beneficial for being generally less harmful than conventional (synthetic) fertilizers, having reduced persistence in the environment, and limiting the development of pathogen resistance for their chemical complexity. Consequently, MAP biomasses represent promising candidates for valorisation as soil amendments. The aim of the present work was to assess the current state of knowledge on the reuse and soil application of MAP residues and to identify the plant species that have been most extensively investigated. An increasing research interest in this topic has been observed, particularly over the last five years. The families Asteraceae, Fabaceae, and Lamiaceae have emerged as those receiving the greatest scientific attention. Four main categories of MAP waste used as soil amendments were identified: fresh biomass, biochar, compost, and solid distillation residues. Overall, the reported outcomes highlight the positive effects of these materials as soil conditioners (improving soil properties, promoting crop growth and limiting weed emergence) and underline their considerable potential. Nevertheless, further research is required to find a proper balance between herbicide and biostimulant effects and optimize the use of MAP-derived residues in soil, especially at field scale.