PHOSPHATE FERTILIZATION OF <em>ACACIA</em> <em>MANGIUM</em>: RESIDUAL OF VARIOUS P-FERTILIZERS AND EFFECT ON UPTAKE OF OTHER ELEMENTS

Abstract

An isotope dilution technique, based on the uptake of labelled phosphorus (³²P), was used to measure the effectiveness of different P sources after incorporation into the soil under Acacia mangium plantation. The phosphate (P) sources tested were Christmas Island rock phosphate (CIRP), Moroccan rock phosphate (MRP), Jordanian rock phosphate (JRP) and triple superphosphate (TSP). Measurements were carried out at 6, 15 and 20 months after fertilizer application. Significant increment in foliage dry matter and P yield was obtained with JRP treated trees at 6 - and 15 - mth sampling. As for the whole tree, the contribution of dry matter weight initially comes mostly from foliage, but at later stages other parts contribute equally or higher. Application of P fertilizer increases the uptake of other nutrients, particularly N and K. The fraction of P taken up by the trees which was derived from fertilization with JRP and
TSP decreased gradually with time. On the other hand, CIRP had a longer residual value. All fertilizers showed relatively comparable P availability for every equivalent unit of material after 20 months of application.