TITRATION PROPERTIES OF Al-ORGANIC MATTER

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Abstract
Because conductimetric titrations and potentiometric titrations have been used to characterize acidity in soil clays, conductimetric and potentiometric titrations of H- and Al-muck were conducted to characterize the nature of acidity in H-, Al-organic matter. Four samples of muck were used as models for soil organic matter. In addition, a carboxylic resin was used for comparison with the natural materials. Results from both potentiometric and conductimetric titrations showed that Al tended to lower the acid strength compared to H-organic matter. Also, Al is hydrolyzed in organic matter, as it is in clays, producing H+ ions and buffering the system against increases in pH. However, complexed Al does not seem to react with base, at least over short periods of time (1 day). Thus, the adsorbed Al is not titratable and tends to lower the effective CEC [cation exchange capacity] and total acidity in organic matter. Whether or not complexed Al reacts slowly with base and affects the lime requirement in mineral soil remains to be determined.

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