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 recovery of corn in acid soil of Sumatra were investigated. The soil was dominated by kaolinitic minerals, very acid and low in extractable phosphorus. The experiment was conducted in two steps: incubation and greenhouse. The treatments were rock phosphate and triple superphosphate (TSP) at 0, 200, 400 and 600 µg P g^-1 for the incubation experiment, and at 0, 50, 100, 150 and 200 µg P g^-1 for greenhouse experiment In the incubation experiment, rock phosphate reduced exchangeable Al and increased pH_H2O better than TSP, and supplied Bray-1 extractable P as much as did TSP. In the greenhouse experiment, apparent P recovery values of rock phosphate were very close to those of TSP and the values tended to decrease at higher rates of P. Although corn yields of the rock phosphate treatment were lower than TSP, its relative agronomic effectiveness was quite high.