Similarities in spectroscopic and physicochemical properties of humic acids from charred grassland plants treated with dil. HNO3 after prescribed burning and from A horizon of Kurobokudo (Ando soils)

摘要

The spectroscopic and physicochemical properties of the humic acids isolated from charred grassland plants after HNO3 treatment (C-HA) and from the A horizon of Kurobokudo (S-HA) were compared. It was shown that: (1) the shapes of the absorption curves in the UV and visible regions of the C-HA and S-HA were featureless, and their humic acids belonged to the A-type; (2) the carbon and hydrogen contents of C-HA were almost the same as those of S-HA, while the nitrogen content of C-HA was much higherthan that of S-HA and the oxygen content of C-HA was lower than that of S-HA. The atomic [O]:[C] and [O]:[H] ratios of C-HA were lower than those of S-HA. These analytical data of C-HA, except for the nitrogen content, fell within the ranges of those ofA-type soil humic acids reported previously; (3) the 13C-NMR spectra of C-HA and S-HA were similar to each other, and the values of their carbon species were in the order: aromatic-C痗arbonyl-C>carbohydrate-C～aliphatic-C. The values of the aromatic-C andcarbonyl-C were lower in C-HA than in S-HA. The reverse was true for carbohydrate-C and aliphatic-C; (4) the FT-IR spectrum of C-HA resembled that of S-HA; and (5) the XRD patterns of C-HA and S-HA indicated that these humic acids had graphite-like structures.