森林立地学会誌 森林立地38(1),1996,53〜61
論 文
はげ山跡地の未熟土壌にみられる土壌発達，
とくに鉱物組成の変化
鳥 居 厚 志
滋賀県田上山（花崗岩地域）と兵庫県三草山（流紋岩地域）を対象に，未熟土壌の成熟に伴う諸性質の変化，とくに鉱物組成の変化を調べた。花崗岩土壌の一次鉱物組成は，土壌の成熟に対応して長石や雲母の比率の変化がみられたが，流紋岩土壌では変化が明確ではなかった．ただし花崗岩土壌，流紋岩土壌ともに磁鉄鉱やジルコンなど風化抵抗性の強い重鉱物の濃縮がみられ，土壌中での定量的な鉱物風化指標としての可能性が示唆された。花崗岩土壌の粘土鉱物組成は，土壌生成の初期から長石や雲母のカオリン化がみられ，成熟に伴って14Å鉱物やギブサイトが生成するプロセスがみられた。流紋岩土壌では土壌生成初期から既に14Å鉱物の生成がみられたが，成熟に伴って長石との比率が逆転する傾向がみられた。これらの分析結果から，花崗岩土壌，流紋岩土壌各々に3−4段階の鉱物の風化ステージが想定された。
Atsushi
TORII: Development of immature soils
after afforestation on bare hills, with special reference to their
mineralogical changes
At one time bare hills caused from
intense human impacts were widely distributed in the Kinki and Setouchi
district, and most of them were afforested later. But soil conditions in these
areas are rather immature even now. Development process of immature soils in
these bare hills were studied with special reference to their mineralogical
changes, weathering of primary minerals and forming of clay minerals. Study
areas were Mt. Tanakami (granite area), Shiga prefecture and Mt. Mikusa
(rhyolite area), Hyohgo prefecture. As for the primary mineral composition of
granite soils, contents ratios of feldspars. mica and other minerals changed
corresponding to the soil development. On the other hand clear changes couldn't
be seen as for the rhyolite soils. But both on granite soils and on rhyolite
soils interesting tendency for particular heavy minerals such as magnetite and
zircon to be concentrated with soil development was found out. And it was
suggested concentration ratio of heavy minerals might be used for quantitative
indicator of weathering stage. Clay mineral composition of granite soils shows
the process that feldspars and mica partly altered to kaolin minerals in early
stage of soil genesis, and in later stage 14Å-minerals and gibbsite were formed. As for the
rhyolite soils 14Å-minerals has
been formed slightly even in the early stage, and it increase gradually in
contrast with decrease of feldspars with soil development. From these results 3
or 4 stages of soil maturity could be presumed both on the granite soils and on
the rhyolite soils respectively.