Physico-chemical and functional characteristics of soil charcoal produced at five different temperatures

The intensity of boreal forest wildfires is highly variable, such that natural wood charcoal can be produced at different peak temperatures. This, in turn, may have consequences on the physico-chemical and functional properties of the charcoal that is returned to soil. We report on a microcosm study where black spruce wood charcoal produced at five peak temperatures (450, 550, 650, 750 and 850 °C) was added to forest soils, and subsequently incubated at room temperature, with and without additions of condensed tannins and/or protein. A fourth experimental factor was added to this full factorial design, which comprised the mixing of soil so as to simulate mechanical scarification in the field. Increasing the charcoal production temperature resulted in higher %C and lower %O and %H, suggesting an increase in aromatic structures. Specific surface area was negligible at 450 °C, was about 50 m2 g−1 at 550 °C, and was 260–300 m2 g−1 at the three highest temperatures. At these higher charcoal production temperatures, 85–90 % of total surface area was attributed to pores