Mineral nutrient distributions in tropical peat soil of Riau, Indonesia with special reference to peat thickness

摘要

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 ＜3 m 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 0.5 m and at 1-2 m above the mineral soil surface. This distribution in the profile corresponds with the boundary thickness of 3 m 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.