Comparative Effects of Biochar and Wood Ash Treatments in Remediating Multi-Element Contaminated Mine Spoil

Abstract

Biochar and wood ash are widely studied materials for amending and remediating metal contaminated soils, but often used in isolation. In this study, a pot experiment was set up to compare their relative effectiveness at restoring soil health. A multi-element contaminated soil from a former metal mining site was treated with biochar, wood ash and compost at three levels (0 - control, 10, 25 and 50 t/ha) and planted with maize for 21 days. Relative effectiveness of treatments was determined by measuring leaf chlorophyll content, plant height, yield, root biomass, and the transfer co-efficient of Cu, Zn and Pb into the foliage. At 10 and 25 t/ha, the wood ash treatment produced relatively higher yield and root biomass, and lower transfer co-efficient of metals than biochar, which is the desired result in phytoremediation. However, at 50 t/ha biochar was far superior to ash in all the variables measured. Thus, both amendments are effective depending on the rate of application. It is recommended that, given the same amount of biomass to be transformed into either wood ash or biochar, ash be the preferred treatment if a large area is to be treated and biochar if the area is relatively small.