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Parts of the tropical peatland in Indonesia are used for plantations such as oil palm and para rubber. This is despite the fact that the mineral nutrient status of the land has not been clearly shown, which may lead to inefficient production and land abandonment. The objective of the present study was to reveal the distribution of each mineral nutrient, i.e. Ca, Mg, K, P and Fe with special reference to peat thickness. Surface (0-25 cm) and subsurface (25-50 cm) peat samples were taken from 42 points in 40 km^2 of oil palm plantation and two points in adjacent forest. Deeper samples were also taken at eight points along two transects to the depth of the mineral soil surface. The ash content, exchangeable bases, total amounts of minerals, and Truog P were determined. The ash content, exchangeable Ca and Mg and total amounts of Mg, K and Fe had a negative correlation with peat thickness, while exchangeable K and Na, Truog P, total Ca and P did not. Some points with a peat thickness of <3m had high mineral contents that correlated with peat thickness, i.e. high mineral contents were found at the edge of the peat dome. In the profile, ash content, exchangeable Ca, Mg, K, and Na were high at the surface 0.5m and at 1-2m above the mineral soil surface. This distribution in the profile corresponds with the boundary thickness of 3m which is considered to be the absorption threshold of these elements by plants. Amounts of fertilizer may be modified based on the distribution of each mineral nutrient.

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大分県の久住高原には厚層多腐植質非アロフェン黒ぼく土が見られる(久保寺ら,2009)。その分布範囲や層序の連続性を広域的に調査するため,久住高原の9地点および九重連山北側の飯田高原の1地点で土壌の層序調査と各層位の理化学性分析,ならびに土壌分類を行った。調査した10断面はいずれも地表から34〜100+cmの範囲に土色1.7/1または2/1の黒色土層が連続し,その下位は黒褐色から褐色の土層となった。多くの断面で黒色土層下部またはその下位に段原降下スコリア(ca. 4.8 cal. ka BP噴出)と考えられる風化礫が見られた。久住高原東側の1断面を除く全てで,表層の黒色土層の上部(段原降下スコリアよりも上位)が非アロフェン質黒ぼく層の化学的要件(Si_o<6g kg^<-1>またはAl_p/Al_o≧0.5または交換酸度y_1≧6)を満たした。これらの非アロフェン質土層は酸性と炭素含量がアロフェン質土層と比べて顕著に高く,また炭素含量が多いものほど高い酸度を示した。厚さ25cm以上の非アロフェン質土層を持ち,日本の統一的土壌分類体系第二次案で非アロフェン黒ぼく土に分類される断面は,九重連山南麓の旧小国街道の北(山側)に分布していた。

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