Effective Alleviation of Aluminum Phytotoxicity by Manure-Derived Biochar

The alleviation of aluminum phytotoxicity to wheat plants in a hydroponic system through the amendment of biochar is investigated to explore the possibility of applying biochar in acidic soil amelioration. Biochar derived from cattle manure pyrolyzed at 400 degrees C (CM400) and the CM400 biochar washed with distilled-deionized water to remove alkalinity (WCM400) were prepared to determine the roles of the liming effect and adsorption during the alleviation of Al toxicity. Upon addition of 0.02% (W/V) CM400 to the exposure solution, the inhibition of plant growth by Al was significantly reduced while the toxic threshold was extended from 3 to 95 mu mol/L Al3+. Due to the biochar liming effect, the aluminum species were converted to Al(OH)(2+) and Al(OH)(2)(+) monomers, which were strongly adsorbed by biochar; furthermore, the highly toxic Al3+ evolved to less toxic Al(OH)(3) and Al(OH)(4)(-) species. Adsorption of Al by the biochar is dominated by surface complexation of the carboxyl groups with Al(OH)(2+)/Al(OH)(2)(+) rather than through electrostatic attraction of Al3+ with negatively charged sites. Compared to the liming effect, the adsorption by biochar exhibited a sustainable effect on the alleviation of Al toxicity. Therefore, the biochar amendment appears to be a novel approach for aluminum detoxification in acidic soils.