Abstract
In order to gain a basic understanding about the relationships between the vertical distribution of organic carbon content of low specific gravity fraction (mainly consists of charred plants) and the soil age or organic C storage in the soil profile of a cumulative Andisol, Miyakonojo, Miyazaki, Japan, forty four soil samples were successively collected from surface and buried horizons (Ap, A, AC and A/C) of the profile. The oldest horizon studied contains the tephra erupted in 12.8cal ka. (1) Microscopic observation of the fraction less than specific gravity 1.6g cm^<-3>, which was isolated after HCl-HF treatment of the soil samples, indicated that the charred plant fragments, which are black or blackish brown, were the main components in this fraction (<1.6 fraction). (2) The total organic C content of the bulk soil (SOC) and organic C content of the <1.6 fraction (POC), ranging from 19.4 to 117 and from <0.5 to 15.8g kg^<-1> dried bulk soil, respectively, were much higher in the 2A (contains the tephra erupted in A. D. 1235) and 4A (contains the tephras erupted in 6.4 and 4.6cal ka) horizons than in the other horizons. No constant relationships were found between the elapse of soil age and the change of POC or SOC. (3) The POC was highly correlated (r=0.875, significant at 0.1% level) with the SOC. Similar relationship was found between the proportion of the POC to the SOC and the SOC (r=0.802, significant at 0.1% level). The POC/SOC value was 5% or more in 17 samples from a total of 44 soils, with a maximum value of 15.2%. (4) From the findings in the present and previous studies, it was assumed that in Japanese Andisol, charred plants contribute to C storage as one of the constituents of soil organic matter.
