FACTORS AFFECTING GYPSUM AND CATION EXCHANGE CAPACITY DETERMINATIONS IN GYPSIFEROUS SOILS1

Abstract

Profiles of gypsiferous soils from the Euphrates basin of Iraq and Syria were studied. Increasing fineness of grinding, from 10, 50, 100, and 170 to 270-mesh, increased the measured amounts of gypsum and soluble Ca + Mg. These variables also increased as the soil:water ratio increased i.e., 1:50, 1:100, and 1:500. Cation exchange capacity values at 10, 100, and 270-mesh sizes were determined by various procedures: N NaOAC/NH4OAC solutions prepared with distilled water and with 1:1 water-acetone mixture; pretreatments of the soil with 2 N Bacl2·2H2O, saturated Na2C2O4, and saturated (COOH)2·2H2O by shaking for variable periods up to six days. After each pretreatment, CEC was determined by the conventional NaOAC/NH4PAC procedure. Highest values were obtained after pretreatment, the order being Na2C2O4, BaCl2·2H2O, and (COOH)2·2H2O. Values increased with time of shaking during pretreatment and with increasing fineness of particle size. Criteria are presented for determining gypsum and CEC in soils containing significant amounts of gypsum.