Field-grown hemp treated with humic/fulvic acids and arbuscular mycorrhizal fungi for phytomanaging a metal-contaminated agricultural soil

Industrial hemp offers several advantages for phytomanaging metal(loid)-contaminated soils as it can provide valuable biomass notably for bioenergy while accumulating some metals (i.e., Cd and Zn) in its shoots. In a previous pot study humic/fulvic acids (HFA) incorporated into the soil with arbuscular mycorrhizal fungi (AMF) enhanced hemp growth. This study assessed the biostimulant effect of HFA, alone or paired with AMF (HFAxAMF), on the shoot yield and shoot Cd, Pb and Zn uptakes in a 2-year field trial in view of producing clean, renewable liquid biofuels. The trial (0.07 ha) was carried out at a contaminated agricultural field in a randomized split-plot design (nine blocks). Cannabis sativa L. was sown at a density of 173 000 plants ha-1. Effects of HFA and HFAxAMF treatments on the behavior of metals and plants were compared to an unamended one. Hemp produced on average 10.7 (year 1)-14.5 (year 2) t DW ha-1 despite a severe drought in year 1. Neither HFA nor HFAxAMF treatments enhanced shoot yield. Shoot Cd, Pb and Zn uptakes reached 9.9, 230, and 869 g ha-1 year-1, respectively. In year 2, shoot Cd uptake improved under all treatments and the 0.01 M Ca(NO3)2-extractable soil Cd, Pb and Zn concentrations at harvest decreased by 95, 79 and 96%, respectively. Hemp was a relevant plant species for phytomanaging this metal-contaminated soil under current climatic constraints. The potential bioethanol yield was estimated in the 3851-6481 L ha-1 range. Overall, hemp can simultaneously reduce soil metal availability while producing a biomass convertible into liquid biofuels. This highlights its strong potential as a dual-purpose crop for sustainable and progressive phytoremediation and renewable energy production.