沖縄島のブナ科が生育する森林土壌の腐植粘土複合体の特徴

抄録

Clay-humus complex has an important role for humic substances are stable in soil. There are many researches about clay-humus complex of volcanic ash soils, but few researches about that of red-yellow soils. In this paper we presented that characteristics for clay-humus complex of red-yellow soils in Okinawa beech forest. Sampling sites were 4 sites, 3 soil samples (3 horizons) were collected in each sites. Clay, silt and sand fractions were in the range of 312〜505 g kg^<-1>, 314〜389 g kg^<-1> and 128〜351 g kg^<-1>, respectively. From X-ray analysis, clay minerals were kaolin minerals, mica and vermiculite-chlorite integrate. Three kinds of humic substance (HS) were extracted and quantified. Two kinds of humic substance were extracted by NaOH and Na_4P_2O_7, humin were not able to extract by both chemical regents. Humin content was higher than other HS fractions. Generally, humin is stable fraction in soil, but other kinds of HS are not stable. Some cations are necessary to stabilize the unstable HS indicated that extractable fraction by regent in soil. Al and Fe content in HS fractions extracted by NaOH and Na_4P_2O_7 were higher than other cations. There were significant relationship between carbon content extracted by NaOH and Ca and Fe with NaOH, and carbon content extracted by Na_4P_2O_7 and Ca and Al with Na_4P_2O_7. These data indicated that HS extracted by both NaOH and Na_4P_2O_7 were stable by these cations. Especially, adding the effects of Fe and Al, calcium may affect the stabilization of both HS types. It is suggested that Fe and Al, Ca are essential to form clay-humus complex in red-yellow soil.