Journal of the Rubber Research Institute of Sri Lanka

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Role of rock phosphates in the nutrition of immature and mature Hevea
(Rubber Research Institute. Agalawatta, 1994) Dissanayake, D.M.A.P. others
Commercially available Eppawela rock phosphate (ERP) was evaluated as a source of P for young rubber plants throughout the period of immaturity. The effects of rock phosphate on yield nutrient composition of leaves soil were also studied on mature rubber.The efficiency of ERP in relation to growth of young plants was similar to that of Imported Rock Phosphate (IRP) Triple Super Phosphate (TSP) when used in soils with a P status less than 37.00 Kg of soils with a soil pH range of 3.6 to 4.2. In these situations it appears that the currently recommended rate of P is unlikely to be sufficient to meet the plant P demand.It is therefore possible to use ERP as a source of P for immature rubber plants growing in areas which are considered low in P for rubber.In contrast, application of rock phosphates did not influence the productivity of the mature rubber tree.plants were able to maintain adequate levels of P in leaves even under no P fertilizer conditions suggesting the effect of residual P in soil that received IRP during the immature phase.