USING BIOCHAR FOR ENVIRONMENTAL RECOVERY AND BOOSTING THE YIELD OF VALUABLE NON-FOOD CROPS: THE CASE OF HEMP IN A SOIL CONTAMINATED BY POTENTIALLY TOXIC ELEMENTS (PTEs)

Hemp (Cannabis sativa L.) is known to tolerate high concentrations of soil contaminants which however can limit its growth and biomass yield. On the other hand, organic-based amendments such as biochar can immobilize soil contaminants and assist hemp growth in soils contaminated by potentially toxic elements (PTEs), allowing for environmental recovery and income generation, e.g. due to green energy production from plant biomass. The aim of this study was therefore to evaluate the suitability of a softwood-derived biochar to enhance hemp growth and promote the assisted phytoremediation of a PTE-contaminated soil (i.e., Sb 2175 mg kg-1; Zn 3149 mg kg-1; Pb 403 mg kg-1; and Cd 12 mg kg-1). Adding 3% (w/w) biochar to soil favoured the reduction of soluble and exchangeable PTEs, decreased soil dehydrogenase activity (by ~2.08-fold), and increased alkaline phosphomonoesterase and urease activities, basal respiration and soil microbial carbon (by ~1.18-, 1.22-, 1.22- and 1.66-fold respectively). Besides, biochar increased the abundance of selected soil culturable microorganisms, while soil metagenome analysis showed a positive influence of biochar on alpha-diversity of the bacterial community and a significantly change of its structure. Biochar did not affect root growth of hemp but significantly increased its aerial biomass, i.e., by ~1.67-fold for shoot, and by ~2-fold for both seed number and weight. Biochar increased the PTEs phytostabilisation potentials of hemp with respect to Cd, Pb and Zn, but also stimulated hemp phytoextracting capacity with respect to Sb. Overall, the results indicated that biochar can boost hemp yield and its phytoremediation effectiveness in soils contaminated by PTEs providing valuable biomass that can generate profit.