Fig. 3. Dissolution of Kanchanaburi rock phosphate with soluble phosphate (KRPS) as represented by the differences in NaOH-extractable-P, Mitscherlich fit curve, and changes of soil pH between KRPS-amended (KRPS 500 mg P kg^–1) and KRPS unamended soils (KRPS 0 mg P kg^–1) in acid sulfate soils.