Field-Based Feasibility Assessment of Sorghum, Maize and Soybean for the Phytomanagement of Heavy Metal-Contaminated Mining Soils in a Living Lab Platform

Heavy metal-contaminated post-mining soils remain persistent sources of ecological degradation and contaminant dispersion. This study provides a quantitative field-based assessment of sorghum (Sorghum bicolor), maize (Zea mays) and soybean (Glycine max) cultivated on heavy metal-affected mining soil from the Jiu Valley, Romania, within a Living Lab platform. Soil properties, pseudo-total metal concentrations, multi-year biomass production, growth indicators, vegetation cover and aboveground plant metal concentrations were evaluated. The soils showed slightly acidic to near-neutral pH, low organic matter and multi-metal contamination, with Cr, Cu, Ni, Zn and Pb ranging from 82 to 146, 51 to 92, 41 to 79, 156 to 287 and 64 to 121 mg kg−1, respectively. Total fresh biomass increased from 85 kg in the first cultivation year to 487 kg in the third cultivation year, with sorghum showing the highest final production (230 kg) and vegetation cover (55–86%). Aboveground Cr, Cu, Ni, Zn and Pb concentrations measured at species-specific levels of 6.21–8.06, 8.77–10.64, 7.48–12.92, 38.01–47.11 and 4.32–6.46 mg kg−1 dry weight, respectively. Sorghum showed the highest preliminary phytomanagement suitability, mainly through stronger vegetation cover formation, higher fresh biomass production and lower visible stress under the investigated field conditions. Maize showed intermediate feasibility, whereas soybean appeared more sensitive to the degraded substrate. Biomass reuse should be considered only under controlled non-food pathways, such as pyrolysis or anaerobic digestion, and should only be considered after a dedicated assessment of dry biomass, conversion residues and metal fate.