Fig. 2. Dissolution of Gafsa rock phosphate (RP) as represented by the differences in NaOH-extractable-P, Mitscherlich fit curve and changes of soil pH between Gafsa RP-amended (Gafsa RP 500 mg P kg^–1) and Gafsa RP unamended soils (Gafsa RP 0 mg P kg^–1) in acid sulfate soils.