Evaluation of Biochar Rate and Hemp Cultivar for the Phytoremediation of Heavy-Metal-Contaminated Soil from the Tar Creek Superfund Site

Soil contamination by cadmium (Cd), lead (Pb), and zinc (Zn) at the Tar Creek Superfund site in Northeast Oklahoma remains a threat to the environment and local ecosystem. Phytoremediation by industrial hemp (Cannabis sativa L.) and the use of biochar (BC) have been independently shown to be effective methods to remediate heavy-metal-contaminated soils. The objective of this greenhouse study was to evaluate the effects of industrial hemp cultivar (‘Carmagnola’ and ‘Jinma’), BC rate (0, 2, 5, and 10% by volume), soil contamination level (low, medium, and high), and their interactions on above- and belowground (AG and BG, respectively) plant dry matter and AG tissue concentrations and uptakes of Cd, Pb, and Zn after 90 days in contaminated soils from the Tar Creek Superfund site. Aboveground dry matter was largest (P \u3c 0.01) in the low-contaminated soil (10.6 g) and smallest in the high-contaminated soil (6.14 g), but was unaffected (P \u3e 0.05) by cultivar. Belowground dry matter was unaffected (P \u3e 0.05) by soil, cultivar, or BC and averaged 2.33 g per plant. Aboveground tissue Cd concentration for the high-contaminated soil was 1.9 and 21.4 times greater (P \u3c 0.01) than the Cd concentration in the medium- and low-contaminated soils, respectively, and was 1.7 times larger (P \u3c 0.01) in the 5 and 10% BC than in the 0 and 2% BC treatments. ‘Carmagnola’ had the numerically largest AG tissue Pb and Zn concentration among both cultivars and was 3.0 times greater (P \u3c 0.01) than in ‘Jinma’ for Pb with 10% BC and 2.4 times greater than in ‘Jinma’ for Zn with 10% BC Results indicate that ‘Carmagnola’ may be a good choice for phytoremediation of Pb-contaminated soils when grown with a BC amendment ≥ 5% (v/v)