SOME CATION-EXCHANGE PROPERTIES OF SOILS CONTAINING FREE OXIDES

Abstract

Low C.E.C. values were obtained for the B horizon of a Concretionary Brown soil from British Columbia and a Podzol from New Brunswick, when CaCl2 was used to saturate the cation-exchange complex. Higher CE.C.'s were obtained if Ca(OAc)2 + CaCl2 was used and this showed that the soils had a large pH-dependent component of the C.E.C. Both soils had a high proportion of pH-dependent charge after the destruction of the soil organic matter. Extraction of free iron oxides increased the C.E.C. of the inorganic exchange fractions and eliminated or decreased the pH-dependent component of the C.E.C. Relatively large amounts of iron and aluminum were removed from the soils by the free oxide extraction procedure. These results suggest that the fixation of aluminum and iron was responsible for the low permanent charge values obtained for the soils. The precipitation of the fixed Al and Fe as Al(OH)3 and Fe(OH)3 when the soils were treated with base or extracted with buffered salt solutions released exchange sites and gave an effect equivalent to the release of exchangeable H so that the soils had a large pH-dependent component of the C.E.C.