Humus Composition of the Plow Layers of Paddy Soils in Yamaguchi Prefecture

The humus cmposition of the plow layers of 15 paddy fields which belong to major soil groups in Yamaguchi Prefecture was analyzed by the method of Kumada and Ohta. The soils, namely 5 gray lowland soils, 3 gley soils, 3 yellow soils, 2 gray upland soils, and 2 brown lowland soils, were used. The results are as follows: 1) No definite relationship was found between the soil groups and the amounts of total humus. However, the degree of humification of humic acids tended to be lower in the gley soils than in the other soils studied. 2) The rations of extracted gumus were free form. 3) The rations of humic acid in extracted humus were around 55% in all soils. 4) Many humic acid showed the combination type of R_P ･ P_O.