THE EXTRACTION OF EXCHANGEABLE CATIONS FROM SOILS

Abstract

A study was made of techniques for the measurement of soil pH and corrected lime potential and for the extraction of exchangeable cations from soils. The experiments showed that in order to obtain stable and reliable pH values and ion concentrations it was necessary to equilibrate the soil samples in CaCl₂ (0.005 to 0.02 M) for 4 to 5 days. After the soil was washed twice with water, the exchangeable cations were extracted from the equilibrated samples by shaking for 16 to 24 hours with 100 ml 2 N NaCl for 0.5 to 2.5 meq of exchangeable cations. In order to obtain reliable values for exchangeable Al with the soils studied, it was necessary to use a colorimetric method instead of titration with NaOH. When these precautions were observed the relation between corrected lime potential and percent base saturation for a number of soils agreed within reasonable experimental error with the theoretical one obtained for Wyoming bentonite.