EXTRACTABLE Fe, Al, Si AND C IN B HORIZONS OF PODZOLIC AND BRUNISOLIC SOILS FROM ONTARIO

Abstract

To investigate the content of amorphous forms of Fe, Al and Si in podzolic soils, the B horizons from 54 Humo-Ferric Podzols and 24 Eluviated Dystric Brunisols were sampled in northern Ontario. Dithionite-citrate-bicarbonate (DCB) Fed and Ald, acid NH4-oxalate Feo, Alo and Sio, Na-pyrophosphate Fep, Alp and Cp and NaOH-tetraborate Fet and Alt were determined on all samples. Feo/Fed ratios averaged 0.87 and suggested that most of the extractable Fe was amorphous. Inorganically bound Fe and Al in pyrophosphate extracts were estimated by addition of NH4OH to the extracts. The amount of inorganically bound Fe, expressed as a percentage of that extracted by DCB, was calculated at 79 ± 23%, whereas the corresponding value for Al was 61 ± 20%. (Alo-Alp)/Sio atomic ratios, plus linear correlation analysis of (Alo-Alp) against Sio, suggested the presence of amorphous aluminosilicates with Al/Si ratios approaching 3. (Feorg + Alorg)/Cp ratios averaged 0.10, a figure near the value suggested by other authors for the maximum amount of Fe and Al bound to organic matter. (Cp/(Fep + Alp) atomic ratios did not appear to be useful in differentiating Podzolic from Brunisolic soils. Key words: Podzolic soils, chemical criteria, extractants