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ARS Home » Midwest Area » St. Paul, Minnesota » Soil and Water Management Research » Research » Publications at this Location » Publication #333810
Title: Glyphosate sorption/desorption on biochars – Interactions of physical and chemical processes

Author
item HALL, KATHLEEN - University Of Minnesota
item Spokas, Kurt
item GAMIZN, BEATRIZ - Collaborator
item COX, LUCIA - Collaborator
item Schneider, Sharon
item KOSKINEN, WILLIAM - University Of Minnesota

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2017
Publication Date: 1/23/2017
Citation: Hall, K., Spokas, K.A., Gamizn, B., Cox, L., Papiernik, S.K., Koskinen, W.C. 2017. Glyphosate sorption/desorption on biochars – Interactions of physical and chemical processes. Pest Management Science. Available: http://onlinelibrary.wiley.com/doi/10.1002/ps.4530/full.

Interpretive Summary: The environmental risk of applied pesticides to soils is often assessed through sorption experiments to guide field management decisions. Recently, biochar has been proposed as a soil amendment that could increase sorption and decrease total chemical transport through the soil system. In this study, we evaluated a series of different hardwood tree biochars created at a range of temperatures (350-900 C) to investigate the mechanisms responsible for the observed sorption relationships with glyphosate. Higher temperature biochar typically resulted in higher sorbed amounts of glyphosate. In addition, the size of the pores in the biochar appeared to influence total sorption capacity. Biochar with higher total amounts of macro-porosity (> 50 microns) possessed the higher glyphosate sorption capacities. Furthermore, it was observe that the sorption of glyphosate was strong relative to water as a desorption solution. On the other hand, when the glyphosate sorbed biochar contacted phosphorus solutions, the glyphosate was readily released to the solution (>85%). Therefore, the sorption strength would be low in soils with high phosphate availability. These results are significant to farmers and policy makers and will assist scientists and engineers in developing improved models for assessing agrochemical fate and effectiveness based on mechanistic processes accounting for the sorption of glyphosate, which should be utilized in developing improved assessments of the fate and transport of applied agrochemicals in biochar amended soils.

Technical Abstract: BACKGROUND: Biochar, a carbon-rich product of biomass pyrolysis, could limit glyphosate transport in soil and remediate contaminated water. The present study investigates the sorption/desorption behavior of glyphosate on biochars prepared from different hardwoods at temperatures ranging from 350°C to 900°C to elucidate fundamental mechanisms. RESULTS: Glyphosate (1 mg L-1) sorption on biochars increased with pyrolysis temperature and was highest on 900°C biochars; however, total sorption was low on a mass basis (< 0.1 mg g-1). Sorption varied across feedstock materials, and isotherms indicated concentration dependence. Biochars with a greater fraction of macropores (> 50 nm) exhibited higher sorption capacities and specific surface groups were also found to be influential. Pre-pyrolysis treatments with iron and copper, which complex glyphosate in soils, did not alter biochar sorption capacities. Glyphosate was not desorbed from biochar with CaCl2 solution; however, up to 86% of the bound glyphosate was released with K2HPO4 solution. CONCLUSION: Results from this study suggest a combined impact of surface chemistry and physical constraints on glyphosate sorption/desorption on biochar. Based on the observed phosphate-induced desorption of glyphosate, the addition of P-fertilizer to biochar-amended soils may remobilize the herbicide and damage of non-target plants; therefore, further assessments are required prior to use.