Determination of exchangeable calcium and magnesium in soil by ion-selective electrode method

The potentiometric measurement of calcium ion activity with a calcium ion electrode and of magnesium ion activity with a divalent cation electrode in the presence of EGTA at pH 7 has been successfully applied to the determination of exchangeable calcium and magnesium in soil after the soil sample is extracted with ammonium acetate and the soil extract is evaporated to dryness and ignited. The results obtained by the ion-selective electrode methods are in good agreement with those obtained by the reference methods.