Abstract
Predicting pyrogenic carbon (PyC) or biochar stability from its precursor properties is critical for evaluating and managing terrestrial C stocks. Transmission mode Fourier transform infrared spectroscopy (FTIR) spectroscopy was compared with proximate analysis data and H/C and O/C for predicting C mineralization. PyC produced at 7 different temperatures from 6 different feedstocks, in addition to the original feedstock materials, was incubated for 3yr at 30°C in a sand matrix. A C debt or credit ratio was calculated by comparing the C remaining in the incubated PyC sample (accounting for the measured C lost during initial PyC production) to the C remaining in the incubated original feedstock. A value>1 indicates that more C remains in the PyC than in the original feedstock (credit), while a value<1 indicates a debt. After 3yr, PyC produced at 300°C lost significantly more C than higher temperature PyC material, but significant differences in C loss between PyC produced at temperatures⩾350°C were not detectable. The best predictor of C loss was a multiple linear regression model using the fractional FTIR signals at 816, 1048, 1374, 1424, 1460, 1590, 1700 and 2925cm−1 as parameters (R2 0.80, p<0.0001). After 3yr, the C debt or credit ratio reached values significantly>1 for all corn PyC samples and some bull, dairy and poultry PyC samples, resulting in net C credit, while all pine and oak PyC samples remained in debt. This C debt or credit ratio reveals that, depending on the timeline of interest, producing relatively low temperature PyC with less initial C loss can result in greater C savings than producing higher temperature PyC, even though the C remaining after exposure to higher pyrolysis temperatures is more stable.
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