Remediation of Cd, Cu, and Zn Metals in Soil Amended with Biochar and Animal Manure Using a Hyperaccumulator

The application of animal manure and organic soil amendments as an alternative to expensive inorganic fertilizers is becoming more prevalent in the USA and worldwide. A field experiment was conducted on Bluegrass–Maury silty loam soil at the Kentucky State University Research Farm using the Kennebec variety of white potato (Solanum tuberosum) under Kentucky climatic conditions. The study involved 12 soil treatments in a randomized complete block design. The treatments included four types of animal manures (cow manure, chicken manure, vermicompost, and sewage sludge), biochar at three application rates (5%, 10%, and 20%), and native soil as control plots. Additionally, animal manures were supplemented with 10% biochar to assess the influence of combining biochar with animal manure on the accumulation of heavy metals in potato tubers. The study aimed to (1) determine the concentration of seven heavy metals (Cd, Cr, Ni, Pb, Mn, Zn, Cu) and two essential nutrients (K and Mg) in soils treated with biochar and animal manure, and (2) assess metal mobility from soil to potato tubers at harvest by determining the bioaccumulation factor (BAF). The results revealed that Cd, Pb, Ni, Cr, and Mn concentrations in potato tubers exceeded the FAO/WHO allowable limits. Whereas the BAF values varied among the soil treatments, with Cd, Cu, and Zn having high BAF values (>1), and Pb, Ni, Cr, and Mn having low BAF values (<1). This observation demonstrates that potato tubers can remediate Cd, Cu, and Zn when grown under the soil amended with biochar and animal manure.