Fig. 9. The percentage reduction in RAE based on the free carbonate (CO₃) content of a phosphate rock (PR) and PR solubility as determined by second extraction neutral ammonium citrate (NAC₂). This example is for a soil with an effective Al saturation (EAlS) of 45%. The solid line represents the calculated line for reduction in RAE for a soil with EAlS of 45%, maize as crop in Fig. 8, and a PR that has no free CaCO₃. The high free CO₃ content of a rock and PR solubility both play a role in reducing the RAE due to EAlS.