AGRONOMIC AND ECONOMIC EFFECTIVENESS OF 2 PHOSPHATE ROCK MATERIALS INACID MALAYSIAN SOILS

The relative agronomic effectiveness (RAE) and relative economic effec tiveness (REE) of Christmas Island phosphate rock (CIPR) and Gafsa pho sphate rock (GPR), compared to triple superphosphate (TSP), were evalu ated in five acid Malaysian soils (pH(w) 4.45-5.0) in a greenhouse exp eriment using the tropical grass Setaria splendida L. as the test crop . There were significant differences between soils in the total dry ma tter (DM) yield of Setaria in 10 harvests spreading over a 20-month pe riod. The DM yield of Setaria decreased in the following sequence: Kun dor > Segamat > Bungor > Tok Yong > Durian soils. The response of Seta ria to the P treatments was clearly indicated by the DM yield and for each soil TSP was superior to either CIPR or GPR. The RAE of GPR (90%) was higher than that of CIPR (72%). However, for the long-term supply of P, both CIPR and GPR were much more cost-effective than TSP, with REE values of 131 and 143% for CIPR and GPR, respectively.