Variations in [Formula: see text] have a pronounced effect on both pH and pH–1/2pCa of non-calcareous near-neutral soils. Consequently it is necessary to specify the [Formula: see text] at which the measurements are made regardless of whether pH or pH–1/2pCa is used to indicate the acidity of these soils.

An advantage of determining cobalt with 1-nitroso-2-naphthol is that the reagent is relatively stable and forms a very stable cobalt complex. Also this cobalt complex has maximum absorption in the visible spectrum which allows determination visually or with ordinary calorimeters. ,The procedure is based on decreasing the iron interference by the removal of part of the iron as phosphate and on a simple purification of the carbon tetrachloride solution of the 1-nitroso-2-naphthol cobalt conlples which eliminates traces of palladium, iron, etc.The method has the same order of accuracy as the o-nitrosocresol method but preparation of reagents and the analysis in general require less time.

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.

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