Fjölrit RALA - 15.06.2004, Page 87

Relationship between Andosolization and Elemental Composition of
Volcanic Ash Soils in Japan
M. Nanzyo and T. Takahashi
Graduate School ofAgrícultural Science, Tohoku University
A characteristic process of Andosolization is preferential formation of noncrystalline
materials such as allophane, imogolite, opaline silica, ferrihydrite, and Al-humus complexes.
No significant tanslocation of Al, Fe and dissolved organic carbon take place. These soil
components are Al- or Fe-rich materials except the opaline silica that is found in the A
horizon of young Andosols. The Si/Al atomic ratio of imogolite is 0.5 and that of allophane
in Andosols is mostly around 0.5 according to selective dissolution analyses.
In contrast, the Si/Al ratio of pyroclastic materials and volcanic glasses, major parent
materials of Andosols, are 4.8-2.4 and 5.2-2.3, respectively. These materials are rich in Si
compared with those of the Al-rich noncrystalline materials mentioned above. Thus, a large
amount of Si is removed during Andosolization, and A1 and Fe is concentrated in Andosols.
It is easily deduced that contents of other elements are also affected during Andosolization.
Table 1 shows the correlation coefficient between oxalate-extractable soil components [Si
(Sio), A1 (Alo) and Fe (Feo)] and total contents of 57 elements. The number of samples is 95
and they were obtained from allophanic Andosol areas of Hokkaido, Tohoku, Kanto, Chubu
and Kyushu districts in Japan. The number of data for 9 elements is less than 95 due to their
very low content.
Significant negative correlation was found between Sio and 4 elements (C, N, Na and Sr),
between Alo and 3 elements (Na, Ca and Sr) and between Feo and 3 elements (Na, Si and K)
at p=0.1%. These elements are alkali and alkaline-earth elements except C, N and Si. Some
other alkali and alkaline-earth elements also tended to show negative correlation with Sio, Alo
and Feo although not as strong. Thus, many alkali and alkaline-earth elements are lost with
Andosolization. The relatively strong negative correlation between Sio and humus content (C
and N) can be explained due to inhibition of allophane formation by humus. The strong
negative correlation between Feo and Si is partly attributable to the properties of parent
materials as well as the Andosolization process. Negative correlation between Fe and Si
content is basically found in fresh tephras having a wide range of rock types.
Significant positive correlation was found between Sio and 24 elements (Be, Al, Sc, Ti, Mn,
Fe, Y, Zr, Nb, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf and Ta), between Alo
and 22 elements (Be, Al, Sc, Ti, Fe, Ge, Y, Zr, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Lu and Hf), and between Feo and 18 elements (Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ga,
Ge, Y, Eu, Gd, Tb, Ho and Er). These elements are concentrated in Andosols during
Andosolization. Due to very high correlation between Sio and Alo, 21 elements among 23
strongly correlated with Sio, also showed high correlation with Alo. Mn and Ta, strongly
correlated with Sio, also showed significant positive correlation with Alo at p=l%.
Ten elements (Al, Sc, Ti, Fe, Y, Eu, Gd, Tb, Ho and Er) that showed strong correlation with
either of Sio and Alo also correlated with Feo. However, 11 elements (Be, Ce, Pr, Nd, Sm,
Dy, Tm, Yb, Lu and Hf) among 21 elements that correlated with both Sio and Alo did not
correlate very strongly with Feo. Other 8 elements (V, Cr, Mn, Co, Ni, Cu, Ga and Ge)
correlated strongly with Feo in spite that they did not correlate with either Sio or Alo very
strongly. All the members of first transition metals from Sc to Cu showed strong correlation
with Feo, adding Sc, Ti and Fe that correlated also with Sio and Alo.
Correlation between oxalate-extractable components and La, Th, U etc. appear weak in
Table 1. However, grouping the samples with rock type of parent materials estimated from V
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