Abstract
The Kurobokudo samples collected from 12 sites in northeastern Japan were fractionated using S. g. 1.6 Mg m^<-3> and 2.0 Mg m^<-3> sodium polytungstate solutions. Both fractions, less than s. g. 1.6 (<1.6 fraction) and s. g. 1.6 to 2.0 (1.6-2.0 fraction), were observed by light and electron microscopy, and the organic carbon contents of these fractions were determined. Also, the humus composition of the soil samples was analyzed. 1) Charred plant particles were the main component in the <1.6 fraction. The charred plant residues of the 1.6-2.0 fraction occurred in association with mineral colloids. 2) The organic carbon content of the <1.6 fraction tended to increase with the increase of that in the 1.6-2.0 fraction. 3) The proportion of organic carbon in the <1.6 fraction to that of the soil sample ranged from 1.7 to 15.9%, and the proportion of 8 samples within 12 samples was more than 6%. 4) The organic carbon content of the <1.6 fraction was correlated with the total humus content, but was not related to other characteristics of the humus composition. 5) All the humic acids belonged to the A-type with a high degree of humification.
