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Rapid Estimation of Cation-Exchange Capacities of Soils and Clays with Methylene Blue Exchange

Department of Agricultural Chemistry, Soil Lab., National Taiwan Univ., Taipei, Taiwan

*Corresponding author (w7350877{at}ccms.ntu.edu.tw).

ABSTRACT

Four methods to determine the cation-exchange capacities (CEC) of soils and clays were evaluated: (i) conventional NH₄-Na exchange, (ii) methylene blue (MB) capacity with MB acid, (iii) CEC of tetrasodium pyrophosphate (TSPP), and (iv) MB-water filter paper spot test titration methods. Eighteen surface soils (0–15 cm) from farm fields in Taiwan and four reference clays obtained from the Source Clay Repository (Clay Minerals Society, Columbia, MO) were used in this work. Under appropriate conditions of concentration, equilibration period, and flocculation of MB solutions, MB absorption can be used to determine the CEC of soils and clays. Regression analyses gave R² values 0.91, 0.99, and 0.74 for MB-acid, MB-TSPP, and MB-water titration methods, respectively, vs. NH₄-Na exchange. The CEC values of MB-TSPP titration showed a good linear correlation with values from the NH₄-Na exchange method. Thus, the method of MB-TSPP filer paper spot-test titration is recommended for rapid CEC determination in field test of soils.

Received for publication December 21, 1994.