THE USE OF pH-DEPENDENT CATION-EXCHANGE CAPACITY FOR CHARACTERIZING THE B HORIZONS OF BRUNISOLIC AND PODZOLIC SOILS

Abstract

A study was made of the pH-dependent C.E.C. as a means of characterizing and differentiating the B horizons of Brunisolic and Podzolic soils. The pH values were measured in 0.01 M CaCl2 after which the soils were extracted with Nacl to determine the percentage base saturation and sum of exchangeable cations. The total C.E.C. values were determined with Ca(OAc)2 + CaCl2 at pH 7 of the untreated soil and of the soils after H2O2 treatment, after extraction with acid ammonium oxalate, and after heating at 200 °C in an atmosphere of N2. The pH-dependent C.E.C. represented by the difference between the C.E.C value determined with Ca(OAc)2 + CaCl2 and the sum of cations extracted with NaCl was found to be small for the B horizons of Brown Forest and Brown Wooded soils. The B horizons of Podzol, Humic Podzol, Acid Brown Wooded, Concretionary Brown, and some Acid Brown Forest soils had high pH-dependent C.E.C. The horizons with high pH-dependent C.E.C. contained significant quantities of amorphous sesquioxide–organic complexes as shown by their relatively high organic matter and free sesquioxide contents and by their exchange properties. The pH-dependent charge appeared to be as effective a primary chemical means of characterizing horizons with spodic properties as were techniques based on the effects of free oxide extraction or heating in N2 on the exchange capacity.