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UBC Theses and Dissertations

Some aspects of buffering of acid soils of the Lower Fraser Valley Wiens, John H.


A study was made to: i) determine the nature of acidity and buffering in acid soils of the Lower Fraser Valley of British Columbia, ii) evaluate and develop methods of predicting buffer capacities of these soils. Results of this study are described in a series of four papers, each describing different phases of this study. The Woodruff and Shoemaker, McLean and Pratt buffer methods proved to be unsuitable for use with these soils when compared to Ca(OH)₂ titration because the buffer pH depression was too small per unit lime requirement and there was considerable scatter about the regression calibration lime. Measurements of lime potential and corrected lime potential as well as pH were found to be significantly correlated with measures of exchangeable acidity but not with measures of pH-dependent acidity. The pH-dependent component of potential acidity was found to be highest for horizons highest in organic matter and in acid ammonium oxalate extractable Al and Fe. Regression equations derived for predicting buffer capacities explained the largest degree of variation of titrable acidity in the pH ranges below pH 5 and above pH 6. The model developed, combining these equations for prediction of buffer capacities to selected end pH values predicted buffer capacities as determined by a Ca(OH)₂ titration reasonably well. Comparison of NaOCl with H₂O₂ for oxidation of organic matter prior to acid ammonium oxalate extraction showed the former to be less destructive to sesquioxides, while at the same time as good or better for the oxidation of organic matter. Results of titrations of soils before and after oxalate extraction following treatment with NaOCl gave inconclusive results with respect to acidity due to the oxalate extractable component. This was due not to the method of removal of organic matter, however, but to uncertainties with respect to the nature of the exchange phase.

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