Bioavailability of phosphorus (P) in soils is controlled by, inter alia, the presence of iron (Fe) and aluminum (Al) oxides, which readily bind with P. Biochar has been suggested for minimizing P sorption to oxides and, therefore, improving P availability to plants. However, the kinetics and temperature dependence of biochar influence on P sorption are poorly understood. The objective of this study was, therefore, to determine the kinetics and thermodynamics of P sorption by goethite as affected by biochar application at 0 and 40 g kg-1 oxide. Batch equilibration tests were run at 15, 25, and 35 °C, and solution P concentrations were measured 0.5, 1, 3, 6, 9, 12, and 24 h after the start of incubation. Sorption of P by the oxides followed pseudo-first-order kinetics. Biochar application enhanced cumulative P sorption by both oxides, and the increase was greater for Al-goethite. Phosphorus sorption increased as temperature increased from 15 to 25 °C but declined at 35 °C. Phosphorus sorption on biochar-amended oxides was associated with low activation energy (Ea) values, indicating that the sorbed P in soils containing goethite and Al-goethite could still be plant available. This information will contribute towards a better understanding of processes affecting biochar effects on P fate in soils.
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Vol. 98 • No. 1