Procedure for Determining Sodium-Calcium Selectivity in Calcareous and Gypsiferous Soils
1990
Amrhein, C. | Suarez, D. L.
A procedure to determine the exchanger-phase composition (and thus the Na/Ca selectivity) of calcareous and gypsiferous soils was developed and tested on three soils and three phyllosilicate minerals. The procedure corrects for anion exclusion and mineral weathering by measuring the Cl, SO₄, and HCO₃ in the soil solution and in the extracting solution. Anion exclusion was found to be significant in the montmorillonite system, but generally less than 10% of the cation-exchange capacity in the soil, illite, and vermiculite systems. Mineral weathering contributed significantly to the total extracted Ca. Thus, exchangeable-Ca values were overestimated by 30 to 500% in the gypsiferous soils and 3 to 20% in the calcareous soils when weathering was neglected. The proposed method allows the determination of cation-exchange capacity, exchangeable-cation composition, and anion exclusion at any solution composition, concentration, and pH. Contribution from the U.S. Salinity Lab., Riverside, CA.
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