Organic matter-sesquioxide complexes in podzol B horizons are precipitated at specific carbon/sesquioxide ratios. Field data indicate that only part of the potential acidity is neutralized and that the maximum C/R2O2 ratio (minimum metal content) at which organic complexes will precipitate depends on pH of the soil and consequently on parent material and profile development. Although C/R2O3 ratios may be used regionally to predict the transition from soluble to precipitated complexes, such ratios cannot be used in soil classification or in a general definition of albic and spodic horizons.
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