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As the global natural forest area continues to decline, tree plantations have an increasing role to provide industrial pulp and timber (Payn et al. 2015). Planted forest area has increased from 167.5 to 277.9 M ha from 1990 to 2015, offsetting the pressure and negative impacts on natural forests (Payn et al. 2015). Tropical plantations with fast-growing tree species as Acacia mangium have increased substantially (Nambiar 2004) due to its rapid growth, good quality of wood and tolerance for nutrient-poor acidic soils (Cole et al. 1996, Norisada et al. 2005). These plantations contribute not only to the wood production but also to providing ecosystem services (Nambiar 2004), including increasing forest surface (Wang et al. 2010) and sequestrating carbon (C) (Zhang et al. 2012), although some plantations have been POTASSIUM AND MAGNESIUM IN LEAF AND TOP SOIL AFFECTED BY TRIPLE SUPERPHOSPHATE FERTILISATION IN AN ACACIA MANGIUM PLANTATION