STUDIES ON THE PROPERTIES OF ORGANIC MATTER IN BURIED HUMIC HORIZON DERIVED FROM VOLCANIC ASH : II. Distribution of Carbon and Nitrogen in Buried Humic Horizon

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In surface horizons (4 samples) and buried humic horizons (14 samples) derived from volcanic ash, the contents of total, fulvic acid, humic acid and humin carbon and nitrogen were determined. The C/N ratios and the percentage of carbon and nitrogen of each fraction in total carbon and nitrogen were calculated. These values varied with each soil profile and horizon. In the surface horizons and the buried humic horizons with age younger than 3,000 yrs. B.P., C/N ratios of soil samples, fulvic acid, and humic acid were low, and those of humin were distributed over a wide range. The C/N ratios increased in the order of fulvic acid, humic acid, humin among these soil samples. Among soil samples which have been buried from 3,000 to 28,000 yrs. B.P., the more were the total carbon contents of soil and also the fulvic acid, humic acid and humin carbon contents, the greater was the tendency of the C/N ratios to rise. The C/N ratios increased in the order of fulvic acid, humin, humic acid among these soil samples. In the buried humic horizons with age over 3,000 yrs. B.P., total carbon content and C/N ratio seem to be controlled by the content of accumulated humus before burial, degradation of the humus after burial, and the rise in C/N ratio of the residual humus, particularly the C/N ratio of the residual humic acid.
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