Correlations between different acidity forms in amorphous loamy soils of the tundra and taiga zones

Pair correlation coefficients (r) between the acidity parameters for the main genetic horizons of soddy-podzolic soils (SPSs), typical podzolic soils (TPSs), gley-podzolic soils (GPSs), and tundra surfacegley soils (TSGSs) have been calculated on the basis of a previously developed database. A significant direct linear correlation has been revealed between the pH_water and pH_KCl values in the organic and eluvial horizons of each soil, but the degree of correlation decreased when going from the less acidic SPSs to the more acidic soils of other taxons. This could be related to the fact that, under strongly acid conditions, extra Al³⁺ was dissolved in the KCl solutions from complex compounds in the organic horizons and from Al hydroxide interlayers in the soil chlorites. No significant linear correlation has been found between the exchangeable acidity (H _exch) and the activity of the [H]⁺ ions in the KCl extract (a(H⁺)_KCl) calculated per unit of mass in the organic horizons of the SPSs, but it has been revealed in the organic horizons of the other soils because of the presence of the strongest organic acids in their KCl extracts. The high r values between the H _exch and a(H⁺)_KCl in all the soils of the taiga zones have been related to the common source and composition of the acidic components. The correlation between the exchangeable and total (H _tot) acidities in the organic horizons of the podzolic soils has been characterized by high r values because of the common source of the acidity: H⁺ and probably Al³⁺ ions located on the functional groups of organic acids. High r values between the H _exch and a(H⁺)_KCl have been observed in the mineral horizons of all the soils, because the Al³⁺ hydroxo complexes occurring on the surface and in the interlayer spaces of the clay minerals were sources of both acidity forms.