Characteristics of buried humic horizons at the Shiiji archeological pits

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Abstract
To investigate changes in the nature of soil organic matter with lapse of time after burial, buried humic horizons derived from volcanic ash with an age from the present to 27,200 YBP were studied and the properties of the soil organic matter in each horizon were assessed. The results for the chemical properties and humus composition of the soil samples were as follows. 1) Based on stratigraphical studies (1), the Ashitaka Loam Formation is divided into two groups of alternate layers, Kuroboku soil in the surface part, and the Upper loam below the Kuroboku soil. The total carbon and nitrogen contents were high in the horizons of the Kuroboku soil and low in the Upper loam. The relationship between the total carbon and nitrogen contents had a positive correlation. 2) The humus compositions of the two groups were as follows. (1) Kuroboku soil: This was characterized by large amounts of humic acid extracted with NaOH and small amounts of both humic acid and fulvic acid extracted with Na6P2O7 Compared with the Upper loam, the Kuroboku soil was characterized by A type humic acid with a lower value of \sDlogK and higher value of RF. (2) Upper loam: The amounts of fulvic and humic acids extracted with NaOH and Na6P2O7 in the buried humic horizons were higher than those of the scoriaceous zones, and tended to decrease with the horizons below. Compared with the Kuroboku soil, the Upper loam was characterized by A type humic acid with a higher value of \sDlogK and lower value of RF.