Pairing energy crops and root biostimulants for phytomanaging a former landfill

Phytomanagement of contaminated soils is increasingly valued both to produce biomass for the bioenergy sector and as nature-based soil remediation option. However, degraded soil conditions may hinder energy crop growth. Biostimulants and micro-organisms could boost crop yield and phytomanagement performance but field-based evidences remain scarce. This study aimed at determining the shoot dry weight (SDW) yield, metal uptake and decrease in soil contaminants for Cannabis sativa, Sorghum bicolor, and Miscanthus × giganteus at a former landfill mainly contaminated by Cu, Zn and PCBs. The 3-year field trial, carried out in a randomized block design, consisted in control plots (C) and plots amended by humic substances paired with mycorrhizal fungi (Hs+M). The technosol exhibited high topsoil stoniness due to abundant debris and an unfavorable sandy-loam texture. SDW yields and metal concentrations (ICP - OES) were measured annually. Sorghum produced the highest SDW yields (3-year average: 20 Mg DW ha^-¹) and responded best to the Hs+M treatment (+16 %-35 %). Treatment did not influence shoot metal concentrations, which tended to decrease over the years. However, higher SDW yields of sorghum increased its shoot Cu and Zn removals (+ 60 % and 46 %-65 % vs. control plants, respectively). Over the three years, shoot Cu uptake was similar for Hs+M sorghum and C hemp. DTPA-extractable soil metals did not change, final soil PCB concentrations as well. Consequently, crops studied would not promote environmental pollutant dispersion. Sorghum paired with the Hs+M treatment was the most promising option, maximizing biomass yield and gradual stripping of bioavailable soil Cu and Zn.