POTASSIUM AND MAGNESIUM IN LEAF AND TOP SOIL AFFECTED BY TRIPLE SUPERPHOSPHATE FERTILISATION IN AN ACACIA MANGIUM PLANTATION

Since nutrients have either synergetic or antagonistic effects, fertilisation has potential to change harvest export of other nutrients present in plantations. In the present research, we investigated the effects of triple superphosphate (TSP) fertilisation on Mg and K contents of leaf and soil pools in a monoculture Acacia mangium plantation in South Sumatra, Indonesia. TSP fertilisation reduced leaf K concentration, but leaf K content per stand area did not show any difference between control and fertilised plots because of the offset by stimulated biomass increment following fertilisation. TSP fertilisation significantly elevated both leaf Mg concentration and leaf Mg content per stand area, indicating the stimulated Mg uptakes by trees. Despite the stimulated uptakes, soil Mg pools were not affected by the fertilisation. It was possibly because the decrease in soil Mg pools during the experimental period was much greater than the stimulated Mg uptakes deriving from the fertilisation. Although the soil nutrient pools were not affected by TSP fertilisation in the present study, our results of the increased leaf Mg contents and the estimated future harvest export of Mg suggest that unbalanced fertilisation can accelerate nutrient export from plantation soils through harvesting.