Studies on a volcanic ash soil at Ohnobaru, Tarumizu City, Kagoshima prefecture

Abstract

Abstract A volcanic ash soil consisting of more than 40 layers, of volcanic fallout was studied from the standpoint of humus chemistry. According to soil texture and humic acid type, the soil profile was divided into 3 sections as follows: (1) Upper layers formed since 1779 A.D. Loamy sand. Po or A type. (2) Middle layers formed from 1779 A.D. to 5,540 yr. B.P. Sandy loam, A, A or P type. (3) Lower layers formed from 5,540 yr. B.P. to about 20,000 D.P. Sandy clay, loam or clay loam, A± type. The PQ values in the middle layers were lower than those of the upper and lower layers. The distribution of carbon and nitrogen contents in the fulvic and humic acid and humin fractions of each layer varied considerably. The CfN ratio of the total humus of each layer tended to increase with the increase in its carbon content. C/N ratios of humic acids in the lower layers were higher than those in the upper and middle layers. C/N ratios of fulvic acid fractions were nearly constant (10-13), for all layers examined, and...