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Hydrogen and Calcium Ion Ratios in Dilute Equilibrium Solutions as Related to Cation Saturation¹

ABSTRACT

Soil samples were collected from field experiments so as to obtain a range in (Ca + Mg) saturation and pH for each soil type. The effects of equilibrating media were studied by comparing water and 0.01M CaCl₂, each at 0.0003 and 0.0108 atm. partial pressure of CO₂. Linear relationships were found for pH – p(Ca + Mg) in the equilibrium solution vs. (Ca + Mg) saturation of the samples. Correlation coefficients ranged from 0.84 to 0.94 and were higher in every case than for pH of suspension vs. (Ca + Mg) saturation. The highest correlation was obtained with samples equilibrated in H₂O and at the higher partial pressure of CO₂. It was also noted that some soils equilibrated in water at the higher level of CO₂ released Ca and Mg to solution more readily than other soils at the same degree of cation saturation. The fact that samples equilibrated in H₂O revealed differences between soils in amounts of Ca + Mg released, whereas, samples equilibrated in CaCl₂ solutions did not, was regarded as an important advantage for studying ion ratios in H₂O solutions. Grouping of soils on the basis of their clay mineral content did not materially improve the correlations. The clay minerals in the soils studied were fairly similar, mostly vermiculite, kaolinite and chlorite, probably in differing amounts.

¹ Technical paper No. 1186, Oregon Agr. Exp. Sta., Corvallis. This paper includes a portion of a thesis submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree at Oregon State College. Presented before Div. II, Soil Science Society of America, at lafayette, Ind., Aug. 8, 1958.

² Formerly Graduate Student, now Research Officer, Experimental Farm, Saanichton, B. C., Canada; and Associate Professor of Soils, respectively.

Received for publication January 19, 1959. Accepted for publication June 29, 1959.