Characteristics of buried humic horizons at the shiiji archeological pits

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Abstract
Changes of sugar components (hexose and uronic acid) with time were determined in surface and buried horizons derived from volcanic ash with an age from the present to 27,200 YBP. The percentages of hexose carbon and uronic acid carbon in acid hydrolysates of the soils to the total carbon of the soils were generally low, ranging from 3.60 to 6.80% and O.S9 to 1.43%, respectively. Humic and fulvic acids were extracted with 0.1 N NaOH and 0.1 N Na4P2O7, and their hexose and uronic acid contents were determined with (humic acid) and without (fulvic acid) hydrolysis. The relationships between the hexose contents and RF values of the humic acid indicated that the higher the humification-degree of A type humic acid, the greater were the amounts of hexose in the humic acid. A highly significant correlation was found between the hexose and uronic acid contents in the fulvic acid and the fulvic acid contents. The correlation between age and U/H values of the fulvic acids indicated that the changes in the sugar components with time were more clearly apparent in the Na4P2O7 extracts than in the NaOH extracts, and that carboxyl groups of the sugar components in the fulvic acid extracted with Na4P2O7 increased with time. Analyses of the sugar components in 75% ethanol precipitates from the fulvic acid extracts showed a similar tendency to that in the fulvic acid extracts.