Biochar Surface Functionality Plays a Vital Role in (Im)Mobilization and Phytoavailability of Soil Vanadium

The potential of biochar with different surface functionalities to immobilize soil vanadium (V) and reduce its phytoavailability has not been studied. We investigated the effects of different doses (0, 2.5, and 5%) of three biochars derived from rice hull and wood residues on fractionation, mobilization, and plant uptake of V in an acidic soil contaminated with V (3750 mg kg-1). Application of wood biochar, with high O-containing functional groups, at 2.5% decreased the water-soluble V by 46% and the soluble + exchangeable V by 32% in soil, as well as reduced the V uptake by corn and sorghum up to 86% in shoots and 65% in roots. Application of wood and rice hull biochars, with low O-containing functional groups, increased V solubility, and thus corn and sorghum were incapable of growing in treated soils. The higher reactive surface, acidity, abundance of various O-containing functional groups, and hydrophilicity of the former wood biochar contributed to its superior performance. Solubility of V increased with the biochar-induced increase of soil pH and dissolved organic carbon (DOC). Soil acidity and aromaticity of DOC are the main factors responsible for V immobilization. These results may help to elucidate the role of biochar in the sustainable management of V-contaminated soils.