Charcoal Fine Residues Effects on Soil Organic Matter Humic Substances, Composition, and Biodegradability

Biochar has been shown as a potential mean to enhance carbon sequestration in the soil. In Brazil, approximately 15% of the produced charcoal is discarded as charcoal fines, which are chemically similar to biochar. Therefore, we aimed to test charcoal fines as a strategy to increase soil carbon sequestration. Charcoal fines of hardwood Mimosa scabrella were incorporated into a Cambisol down to 10 cm (T1 = 0 and T4 = 40 Mg ha(-1)) in Southern Brazil. Soil samples were collected (0-30 cm) 20 months after charcoal amendment. Soil organic matter (SOM) acid extract, humic acid, fulvic acid, and humin fractions were separated. Solid-state C-13 nuclear magnetic resonance (NMR) spectra from charcoal and SOM in T1 and T4 were obtained before and after 165 days of incubation under controlled conditions. Charcoal increased soil carbon as fulvic (10-20 cm) and humic acids (10-30 cm) and, especially, as humin (0-5 cm), which probably occurred due to the hydrophobic character of the charcoal. The C-13 NMR spectra and mean residence times (MRT) measured from incubation essays indicated that the charred material decomposed relatively fast and MRT of T1 and T4 samples were similar. It follows that the charcoal fines underwent similar decomposition as SOM, despite the high charcoal dose applied to the soil and the high aryl C contribution (78%) to the total C-13 intensity of the charcoal NMR spectra.