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Open AccessArticle

Variation in Feedstock Wood Chemistry Strongly Influences Biochar Liming Potential

Centre for Biocomposites and Biomaterials Processing, Faculty of Forestry, University of Toronto, Toronto, ON M5S 3B3, Canada
Department of Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, ON M5S 3G8, Canada
Faculty of Forestry, University of Toronto, Earth Sciences Building, 33 Willcocks Street, Toronto, ON M5S 3B3, Canada
Author to whom correspondence should be addressed.
Soil Syst. 2019, 3(2), 26;
Received: 4 February 2019 / Revised: 26 March 2019 / Accepted: 27 March 2019 / Published: 3 April 2019
Chars intended for use as soil amendment (“biochars”) vary greatly in their chemical and physical properties. In the present study, 19 Canadian temperate wood feedstocks were charred across a range of pyrolysis temperatures from 300–700 °C. The resulting 95 biochars were tested for their physio-chemical properties and liming capacity. Data indicated increasing base cation concentrations including Ca, Mg, and K (elements that characteristically form liming compounds, i.e., carbonates) as pyrolysis temperature increased. Acidic surface functional groups were analyzed with modified Boehm titration: Carboxylic and lactonic functional group concentrations decreased and phenolic group concentration increased with pyrolysis temperature. Functional group composition also varied greatly with feedstock: In particular, conifer-derived biochars produced at pyrolysis temperatures <500 °C showed much higher carboxylic and lactonic functional group concentrations than did angiosperm-derived biochars. Liming capacity was assessed using soil incubation experiments and was positively related to biochar pH. Both acidic surface functional group concentration and nutrient element concentration influenced biochar pH: we developed a non-linear functional relationship that predicts biochar pH from the ratio of carboxylic to phenolic moieties, and concentrations of Ca and K. Biochar’s liming components that are inherited from feedstock and predictably modified by pyrolysis temperature provide a basis for optimizing the production of biochar with desired pH and liming characteristics. View Full-Text
Keywords: acidic groups; cations; char; pH; pyrolysis acidic groups; cations; char; pH; pyrolysis
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Gezahegn, S.; Sain, M.; Thomas, S.C. Variation in Feedstock Wood Chemistry Strongly Influences Biochar Liming Potential. Soil Syst. 2019, 3, 26.

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