EFFECT OF ROCK PHOSPHATE ON SOIL PROPERTIES AND APPARENT PHOSPHORUS RECOVERY IN ACID SOIL OF SUMATRA

The effects of rock phosphate (RP) on soil properties and apparent P r ecovery of corn in acid soil of Sumatra were investigated. The soil wa s dominated by kaolinitic minerals, very acid and low in extractable p hosphorus. The experiment was conducted in two steps: incubation and g reenhouse. The treatments were rock phosphate and triple superphosphat e (TSP) at 0, 200, 400 and 600 mu g P g(-1) for the incubation experim ent, and at 0, 50, 100, 150 and 200 mu g P g(-1) for greenhouse experi ment In the incubation experiment, rock phosphate reduced exchangeable Al and increased pH(H2O) better than TSP, and supplied Bray-1 extract able P as much as did TSP. In the greenhouse experiment, apparent P re covery values of rock phosphate were very close to those of TSP and th e values tended to decrease at higher rates of P. Although corn yields of the rock phosphate treatment were lower than TSP, its relative agr onomic effectiveness was quite high.