Studies on the properties of organic matter in buried humic horizon derived from volcanic ash |
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Authors: | Masao Yoshida Kyoichi Kumada |
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Affiliation: | Faculty of Agriculture , Nagoya University , Nagoya , 464 , Japan |
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Abstract: | Abstract Humic acids were extracted from the surface horizon Yu 1 and buried humic horizons (Yu 2, 800-864 AD; Yu 4, ca. 4,000 years B.P.; Yu 6, 7,000 years B.P.; Yu 7, ca. 10,000 years B.P.). The humic acids were filtered with ultramembranes with 20, 10, 5, 1 or 0.1 × 10' M.W. in this order and separated into five fractions; (>20), (20-10), (10-5), (5-1) and (1-0.1) × 104 M.W. fractions. The elementary composition, functional groups, optical properties, and hydrolyzable total- and sugar-carbon contents of each humic acid fraction were determined, and the changes in properties of the humic acid with age after burial were discussed. In horizons Yu 1 to Yu 6, the patterns of M.W. distribution of the >20 × 104 to (1- 0.1) × 104 fractions were rather similar. In contrast, Yu 7 was characterized by the predominance of (1-0.1) x 10' M.W. fraction and the presence of a small amount of <0.1 × 104 M.W. fraction. The chemical properties of humic acid (HA) fractions of each humic horizon and their changes with age after burial were as folIows: 1) Elementary composition of HA fractions of each humic horizon was rather similar to each other. The C% and C/N ratio increased, and the H%, N% and H/C ratio decreased in all HA fractions with age. 2) Total acidity and carboxyl contents of HA fractions of Yu 1 were higher in the lower M.W. fractions. These values increased with age up to Yu 4 or Yu 6 horizons, then decreased in the Yu 6 or Yu 7 horizon. The contents of carbonyl groups in all the HA fractions which were very low in Yu 1, showed a wide range of variations in Yu 2, intermediate values from Yu 4 to Yu 6 horizons then decreased in the HA fractions of Yu 7, except for the (>20) fraction. 3) The degree of humification of the HA fractions of Yu 1 judging from the RF and sDlogK values, tended to be higher in higher M.W. fractions, and increased in all the HA fractions with age after burial. 4) Hydrolyzable total- and sugar-carbon contents were high in the HA fractions of Yu 1 and decreased with age. 5) Changes of elementary composition, degree of humification and hydrolyzable total- and sugar-carbon contents were conspicuous from the Yu 1 to Yu 2 horizons, and less significant afterwards. 6) The 0%, C/O ratio and phenolic OH content did not show any consistent change with age after burial. |
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Keywords: | buried humic horizon humic acid organic matter ultramembrane filtration |
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