Kinetics of phosphorous sorption to biochar-amended soils

Authors: Bolster, Carl

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2023
Publication Date: 10/23/2023
Citation: Bolster, C.H. 2023. Kinetics of phosphorous sorption to biochar-amended soils. Chemosphere. 345. Article 140523. https://doi.org/10.1016/j.chemosphere.2023.140523.
DOI: https://doi.org/10.1016/j.chemosphere.2023.140523

Interpretive Summary: Biochar has been investigated as a potential soil amendment to increase P retention in agricultural soils to minimize off-site P losses to protect water quality. Treating biochar with iron (Fe) oxides and hydroxides has been shown to be effective for increasing P sorption to biochar and when added to soil can increase P sorption and reduce its leaching through soil. Few studies, however, have investigated how the addition of Fe-coated biochar affects P sorption to soils over time. In this study, P sorption was measured at various times ranging from 15 min to 314 hours in four soils with contrasting surface properties and textures over. Treatments included a wood-based biochar either unmodified or coated with Fe-hydroxide. Results showed that the unmodified biochar had minimal impact on P sorption to the four soils, whereas the addition of the Fe-coated biochar increased P sorption to all soils, though the magnitude of the increase varied depending on soil. In the low P sorbing soil, the Fe-coated biochar nearly doubled the amount of sorbed P while in the high P sorbing soil, addition of the Fe-coated biochar resulted in less-than-expected increases in P sorption. This study provides new insights into P sorption to biochar-amended soils.

Technical Abstract: Biochar has been investigated as a potential soil amendment for increasing P sorption to soils. Several studies of shown that coating biochar with Fe oxides can increase the amount of P sorbed to the biochar. Few studies, however, have investigated how the addition of Fe-coated biochar affects the kinetics of P sorption to soils. In this study, the kinetics of P sorption are measured in four soils with contrasting surface properties and textures. A wood-based biochar, both unmodified (BC) and modified by chemical precipitation of Fe-OH (BCFe), was added to these four souls at a rate of 5% (w/w). P sorption to each soil with and without the unmodified or Fe-modified biochar was measured at incubation times ranging from 0.25 to 314 hr. The data were fit using five different kinetic models to determine if the addition of the BC or BCFe significantly affected the amount of P sorption and the kinetic behavior of the P sorption. Results showed that the unmodified BC had minimal impact on P sorption to the four soils, whereas the addition of the BCFe impact varied depending on soil. In the low P sorbing soil, the BCFe nearly doubled the amount of sorbed P while in the high P sorbing soil, addition of the BCFe resulted in less-than-expected increases in P sorption. For each biochar and soil treatment, the same kinetic model provided the best fit to the observed sorption over time. In two soils, the kinetic model parameters were significantly different following addition of the BC whereas the model parameters for all four soils were significantly different following addition of BCFe. This study provides new insights into P sorption kinetics to biochar-amended soils.