Determination of Cation Exchange Capacity of Calcareous Soils: Comparison of Summation Method and Direct Replacement Method

The purpose of this study was to compare cation exchange capacity (CEC) values obtained by direct measurement and by summing the exchangeable base cations (EBCs) in calcareous soils. The seven soils used in this study were collected in Nassau, Bahamas, and in south Florida. The collected soils were analyzed for pH, organic matter, calcium carbonate, CEC, and EBCs. The CEC was determined using Bower's method with slight modification, which featured 1 M sodium acetate at pH 8.2 as saturating solution, 70% ethanol for washing, and 1 M ammonium acetate at pH 8.2 for extracting adsorbed sodium ions. The extracted sodium ions were quantified using an inductively coupled plasma-optical emission spectrometer (ICP-OES). The exchangeable base cations were extracted using 1 M ammonium acetate solution at pH 8.2 and quantified by ICP-OES. The cation exchange capacity values determined by the direct method and summation method were comparable for all the soils used in this study. Summation CEC was not significantly different from the measured CEC (p < 0.05) for all the soils. These results imply that the summation method based on EBCs extraction with 1 M ammonium acetate at pH 8.2 may be a viable choice for soil testing laboratories to accurately estimate CEC in calcareous soils.