CHEMICAL STUDIES OF PODZOLIC ILLUVIAL HORIZONS

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Abstract
Summary: A study of the effects of concentration of aqueous acetylacetone, extraction time, and of pH on the extraction of organic carbon and sesquioxides from four widely distributed podzol B horizons is reported. Reaction time has little influence on carbon extraction, but increasing reagent concentration causes, in general, an increase in carbon dispersion. Amounts of ether‐extractable Fe and A1 (removed as complexes of acetylacetone) increase directly with both concentration of reagent and time of contact. 0.2 M acetylacetone at pH 7 removes more carbon and in some cases more Al complex than at pH 4–2, but less Fe is extracted at the higher pH value. Pyrophosphate is more efficient than acetylacetone at the same concentration and pH, and tends to extract more Al and carbon, but less Fe. Sedimentation experiments suggest that the proportions of Al, Fe, and SiO2 remaining in some organic‐matter suspensions are physically distinct from the carbon fractions. An indurated iron‐humus pan from New Zealand yelded very small amounts of ether‐extractable Fe, suggesting that Al may play a predominant role in stabilizing the organic matter in this soil. Some of the extraction data given for the other soils suggest that A1 is likely to act in this way and it is suggested that the function of A1 in podzolization, previously assigned a secondary role, has possibly been overlooked.

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