Abstract
The results obtained were as follows. 1) Among 36 forest soil samples of four different soil types, the amounts of organic and inorganic soil components studied which are responsible for proton consumption were quite variable, even within those samples from the same soil type. 2) According to a cluster analysis using nine variates of Ex-Ca, Total-C, Pyr-Al, Pyr-Fe, Ox-Si, Am-Al, Am-Fe, Ex-Al and BS (base saturation degree), five clusters of soil samples were differentiated, where each bluster reflected the difference in the nature of parent materials and the value of BS. Namely, cluster 1 (C1) comprised those samples derived from basic and ultra-basic rocks, cluster 2 (C2) from volcanic ashes of mafic composition, cluster 3 (C3) from acidic rocks, cluster 4 (C4) from volcanic ashes of felsic nature, and cluster 5 (C5) comprised 3 other samples. C1 and C2 samples showed BS of more than 30%, while C3 and C4 less than that. 3) By the use of principal component analysis, components 1 and 2 extracted from the covariance matrix of four variates of Pyr-Al, Ox-Si, Am-Fe and BS, explained about 90% of the variability of the 36 soil samples' matrix. Moreover, the "potential buffering capacity" of the soils was evaluated by the sum of points obtained from the square-root of each percentage of total variance multipied by the characteristic value of components 1 and 2. The results showed that the decreasing order of points was as follows : C5>C2>C1>C4>C3 samples. 4) By the application of a multivariate regression analysis, the variate extracted to explain the amounts of proton consumption by soil samples in each cluster were as follows : C1, Total-C and Ox-Si ; C2, Ex-Cation; C3, Ex-Cation, Pyr-Al and Ox-Si ; C4, Pyr-Al ; and for all samples, Ex-Cation, Pyr-Al and Am-Fe. 5) Among the different organic and inorganic soil components, Ex-Cation showed the most reactive component during proton consumption. However, the stepwise acid neutralizing mechanism (YOSHIDA and KAWABATA 1986) seems to be less plausible, as shown by this study, and to be rather strongly affected by the amounts and composition of each soil component responsible for proton consumption.
