Rapid assessment of black carbon in soil organic matter using mid-infrared spectroscopy

Comprehensive data sets for understanding the global distribution of black carbon (BC) in soil are lacking because the currently available methods are too time consuming for routine monitoring of BC in the environment. Here we report that reliable screening of soil BC can be achieved using mid-infrared spectroscopy (MIRS) and multivariate data analysis. Calibration models were built employing 309 samples from different soil depths and land use systems in America, Asia and Europe, characterized for soil organic carbon (SOC) and benzene polycarboxylic acids (BPCAs) as specific BC markers. About 99% of total SOC variability was explained by local calibrations with an error of prediction < 0.1 g SOC kg−1 soil. In addition, BPCA carbon was assessable. The precision was lower (R2 > 0.8), partly reflecting different BC quality. A measure of the latter is the mellitic acid carbon percentage. This also correlated with MIRS patterns (R2 ⩾ 0.6), which therefore even allowed classification of BC according to its degree of aromatic condensation.