DISSOLUTION DES COMPOSÉS FERRUGINEUX ET ALUMINEUX DES HORIZONS B PODZOLIQUES DE SOLS DU QUÉBEC PAR LE DITHIONITE-CITRATE-BICARBONATE, L'OXALATE, LE PYROPHOSPHATE ET LE TÉTRABORATE

Abstract

Organic matter, Fe and Al were determined in dithionite-citrate-bicarbonate (d), oxalate (o), pyrophosphate (p) and tetraborate (t) extracts from Quebec Podzolic B horizons in order to evaluate the ability of these reagents to extract the organo-metallic complexes as well as inorganic oxides and hydroxides, and to verify the appropriateness of soil classification criteria. Dithionite solubilized most of the Fe whereas oxalate extracted most of the Al compounds; the ability of the same reagents to extract Al and Fe, respectively, was directly related to the amount of organo-metallic complexes. Pyrophosphate extracted not only complexes but also inorganic compounds while tetraborate extracted mainly complexes. Organic matter extraction by dithionite, oxalate and tetraborate was enhanced by a high fulvic acid content; it was highest in the Bh and lowest in the Bf horizons. Organic matter, Fe and Al extraction by tetraborate was reduced in the presence of a large Fe-inorganic compounds content. These results indicated that extracting ability of the reagents depends on the nature of the B horizons, except for Fe extraction by dithionite and Al extraction by oxalate. Consequently, Fe and Al extraction by pyrophosphate or tetraborate is not appropriate for classification purposes. Differentiation of Bh horizons from other Podzolic B horizons was possible by using the total organic C to Fe_d + Al_o ratio, because the ratio was > 3 for Bh horizons and < 3 for Bf and Bhf horizons. Key words: Organic matter, iron, aluminum, Podzolic B horizons, extraction reagents