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This article in SSSAJ

  1. Vol. 51 No. 4, p. 908-912
    Received: Sept 2, 1986

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Significance of Potassium Chloride pH of Calcareous Soils1

  1. T. J. Moore and
  2. R. H. Loeppert2



The use of high ionic-strength media for determination of soil pH has been limited primarily to acid soils. In this study, the theoretical and practical significance of the pH of calcareous soils suspended in 1 M KCl was investigated. Solutions from suspensions of 24 soils in 1 M KCl were analyzed for pH, Ca, Mg, Na, K, and alkalinity, and equilibrium relations were evaluated. In addition, the equilibrium relations of standard calcite samples were investigated in 1 M chloride solutions at different Ca to K ratios. Suspensions of calcite were in equilibrium with respect to CaCO3; however, soil suspensions were supersaturated (Ω = 1-3). The KCl pH values of calcareous soils were inversely related to both the Ca concentration of the KCl extract and the cation exchange capacity (CEC) of the soil. The role of K+ was to displace Ca2+ from the cation exchange complex. Increased Ca in the KCl extract resulted in a decrease in pH, as predicted from the equilibrium relations of calcite. The use of KCl pH with calcareous and acid soils is analogous in that the pH reflects CEC and the cationic composition of the exchange complex. As with acid soils, the KCl pH of calcareous soils may provide valuable precursory information concerning the chemical properties of the system.

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