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A New Method for the Simultaneous Measurement of pH-Dependent Cation Exchange Capacity and pH Buffering Capacity

^a Lab. for Soil and Water Management, Faculty of Agricultural and Applied Biological Sciences, Kasteelpark Arenberg 20, 3001 Leuven/Heverlee, Belgium
^b Soil Microbiology Unit, International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria, c/o Lambourn, Carolyn House, 26 Dingwall Road, Croydon CR9 3EE, UK
^c Present address Tropical Soil Biology and Fertility Program, Unesco-Gigiri, PO Box 30597, Nairobi, Kenya

View larger version (18K): [in a new window]   Fig. 1. Cation exchange capacity-pH relationships obtained by the modified silver-thiourea (AgTU) method. Regressions lines shown are fitted for the results from the proposed procedure.

View larger version (24K): [in a new window]   Fig. 2. Effect of equilibration time after addition of 0.05 or 0.1 mL of HNO3 (1 M) on the pH and cation exchange capacity (CEC) of the soil. Error bars indicate the standard error of the difference (SED).

View larger version (18K): [in a new window]   Fig. 3. Cation exchange capacity (CEC)-pH relationships after shaking alternately for 16 or 4 h (solid lines) or after always shaking overnight (broken lines).

View larger version (18K): [in a new window]   Fig. 4. Comparison of cation exchange capacity (CEC)-pH relationships determined by the modified silver-thiourea (AgTU) method (solid lines), the buffered AgTU method (broken lines) and the ion adsorption method (dotted lines). Data points presented are averages of four (modified AgTU method) or three (buffered AgTU and ion adsorption method) replicates. All regressions are significant at P 0.0001.

View larger version (12K): [in a new window]   Fig. 5. Linear part of the buffer curves obtained by the proposed modified silver-thiourea (AgTU) method for the three soils selected. The pH buffer capacity (pH BC) was estimated as the reciprocal of the slope of the regression lines. Regression equations and pH BC are reported in Table 2.