Effect of biochar and Fe-biochar on Cd and As mobility and transfer in soil-rice system.

In this study, the effects of biochar derived from rice-straw (biochar) and iron-impregnated biochar (Fe-biochar) on Cd and As mobility in rice rhizosphere and transfer from soil to rice were investigated with different application rates. 1-3% biochar reduced porewater Cd in rhizosphere but elevated soluble As, resulting in 49-68% and 26-49% reduction in the root and grain Cd, with a simultaneous increase in root As. Unlike biochar, 0.5% Fe-biochar decreased porewater As throughout rice growth, resulting in reduced root As, which, however, increased Cd uptake by root. Biochar-induced soil As mobilization was probably through competitive desorption and Fe-biochar-induced soil Cd mobilization was probably via soil acidification. The results suggested that biochar and Fe-biochar was effective in reducing Cd and As uptake by rice, respectively, so they may be used as emergency measures to cope with single Cd or As contamination in paddy soils.