Leaching behavior of Cd, Zn and nutrients (K, P, S) from a contaminated soil as affected by amendment with biochar

In Campine region in Flanders (Belgium) there are contaminated sites with Cd and Zn due to atmospheric deposition from industry. Flanders is also known for its large surpluses of nitrogen and phosphorous coming from intense livestock production. To solve both issues, the potential of biochar to sorb metals and nutrients was investigated. Experiments were conducted to examine whether biochar could reduce the leaching of nutrients (K, P and S) and metals (Cd and Zn) into the soil solution. Most biochars caused an increase in pH of approximately 1 unit which is often the main driver of the metal immobilization. Nutrient concentrations in the leachate of soil amended with oak-based biochar were lower compared to the blank soil. For the other amendments, however, the results were higher due to the nutrients leached from the applied products. The result of this experiment emphasize the potential of biochar to immobilize nutrients and metals in soil water systems, thus keeping the nutrients longer available for the plant and reducing the metal toxicity. However, the amount of metals immobilized was lower than expected. Further research is required to determine whether biochar from livestock products could act as a slow release fertilizer.