Fjölrit RALA - 15.06.2004, Page 98

The quantity of base cations released to the abrasion solution is very low in all the studied
horizons (Ca+Mg+Na+K<0.5 emolc/kg), with the lower concentrations in the soils from
France and Azores (0.03-0.1 emolc/kg). The only exception is the soil from Hungary, with
abnormally high contentent in all the measured cations. The composition of abrasion solution
has no relation to the abrasion pH neither to other parameters generally related to the potential
fertility of soils like the total reserve of bases (TRB). Only K and Ca in exchange complex are
relatively well correlated to their concentration in abrasion solution (r2=0,771 and =0,638
respectively, for most but not all samples).
Weathering index of Parker vs abrasion pH in volcanic soils
In conclusion, abrasion pH can be interpreted, in a very general way, in terms of weathering
or pedogenetic evolution in the soils of volcanic regions and also may serve as a tool to
understand the complex processes that frequently occur in these soils (heterogeneity of parent
material, burial processes, tephra inputs, polygenesis). Nevertheless, the mentioned
complexity can also hmit the use of this single parameter. As the value of abrasion pH
depends on the chemical and mineralogical composition of the material, but also on the
physicochemical behaviour of the new surfaces created during the grinding process, many of
the unusual characteristics observed in the abrasion pH and abrasion solution composition of
volcanic soils are to be linked to the special constituents and properties that characterize these
soils, in particular their charge properies and the effects that grinding may produce on them.
This represents a disadvantage of the method but it may also help to the understanding of the
behaviour of these soils and their components when the obtained information is analyzed in
detail for each particular soil or horizon.
References
Grant, W.H., 1969. Abrasion pH, an index of chemical weathering. Clays and Clay Miner.
17:151-155.
Ferrari, G.A., and D. Magaldi. 1983. Degree of soil weathering as determined by abrasion pH:
Applications in soil study and paleopedology. Pedologie 33:93-104.
Parker, A. 1970. An index of weathering for silicate rocks. Geol. Mag. 107:501-504.
Price, J.R., and M.A. Velbel. 2003. Chemical weathering indices applied to weathering
profiles developed on heterogeneous felsic metamorphic parent rocks. Chem. Geol.
202:397-416.
Stevens, R.E., and M.K. Carron. 1948. Simple field test for distinguishing minerals by
abrasion pH. Am. Mineralogist 33:31-49. In Grant (1969).
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