Potentials of Biochar to Improve Productivity of Automobile Wastes Contaminated Ultisol under Mound Tillage Practice Using Cocoyam (Xanthosoma sagittifolium) as Test Crop in Abakaliki Southeast Nigeria

A field experiment was conducted in 2018 and 2019 cropping seasons to evaluate the effect of biochar on the physicochemical properties of automobile waste contaminated soil, yield, soil heavy metal (Cu, Zn, Fe, Pb) content and uptake by Cocoyam (Xanthosoma sagittifolium) in a mound tillage practice. The treatments were; Contaminated automobile waste soil (CO-control), contaminated soil amended with 5 tha⁻¹ biochar (BO₅), contaminated soil amended with 10 tha⁻¹(BO₁₀) and contaminated soil amended with 20 tha⁻¹ biochar (BO₂₀). There was significant decrease in soil bulk density and increased soil hydraulic conductivity in biochar amended plots compared to the control. Exchangeable bases (Ca, Mg, K, Na), effective cation exchange capacity (ECEC), total N, available P, organic carbon and pH levels were significantly higher in biochar amended plots relative to the control. The significantly higher cocoyam yield was recorded in the biochar amended plots compared to control plots. Biochar amendment reduced the levels of Pb, Fe, pb and Cu to tolerable limits in soils. Similarly, uptake of Fe, Zn, cu and Pb by cocoyam in biochar amended soil was within acceptable limit for human consumption. It is recommended that agronomic practices that increases soil nutrient and decrease heavy metal uptake be used in automobile waste contaminated soils to obtain high crop yield and safe produce.