The dark-red forest soils of the Ogasawara Islands (I)

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Other Title
  • 小笠原諸島の暗赤色を呈する森林土壌について (I)
  • 小笠原諸島の暗赤色を呈する森林土壌について-1-環境条件,形態,粒径組成,ならびに一般化学性について
  • オガサワラ ショトウ ノ アンセキショク オ テイスル シンリン ドジョウ ニ
  • 環境条件,形態,粒径組成,ならびに一般化学性について
  • Site condition, and morphological, mechanical and chemical properties

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Description

Dark reddish soils are widely distributed in the Ogasawara Islands which belong to the humid-subtropical zone. The soils cor-respond to the Dark-red Soil Group under the forest soil classification “1975” of Japan. The soil-forming process of this soil group has scarcely been made clear even today. As similar soil of the group are adaptively developed in tropical areas, studies on the soil-forming process can be better conducted on these sub-tropical islands than on mainland Japan. In this report primarily site conditions and chemical properties were investigated. The activity and results are summarized as follows; (1) volcanogenous and eutric sub-groups of the dark-red soils were observed; (2) the soils are formed from various types of material in the islands, whereas the soils are related mainly to limestone and serpentine on the mainland; (3) eutric dark-red soil is very heavy in texture, and the clay content increases in the sub-horizon; (4) exchangeable base content is high in eutric dark-red soil, and the pH is high in reflection of the high base content (over 50 percent in base saturation), whereas volcanogenous dark-red soil is strongly acidic with high exchangeable acidity and low base saturation; and (5) the types of exchangeable bases of eutric sub-group soils reflects the quality of the parent material, in that the soil has a high Ca proportion in exchangeable bases from calcareous parent material and a high Mg proportion from magni-ferrous material.

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