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Further Characterization of Arkansas Soils by Cationic Activity Measurements¹

ABSTRACT

To determine the predominant clay minerals in various southern U. S. soils, five soils and four extracted colloidal materials were characterized by means of the clay membrane electrode technique for measuring ionic interactions. The study dealt with two additional Ruston soils, two additional Sharkey soils, the same Houston soil as was previously studied, and three clay separates and one crude humic acid fraction from this Houston soil.

From the cationic activity values, the fractions of K active were computed and plotted against K - Ca saturations to obtain curves for comparison with those characteristic of the individual clay minerals.

The results indicate that even though kaolinite is doubtlessly present in considerable quantity in the Ruston soils, montmorillonite clay appears to exert a strong if not dominant influence in regulating the cationic interactions in these soils. Beidellite clay seems to play the major role in the Sharkey and Houston soils. Although not as striking as was found in the case of the Sharkey soil studied previously, the <25 mµ fraction from the Houston soil seems to be influenced by montmorillonite. The 50 to 200 mµ fraction is more characteristic of beidellite, and the 25 to 50 mµ fraction is intermediate between montmorillonite and beidellite in characteristics of the K active — base saturation curve. The crude humic acid fraction separated from the Houston soil was found not to be markedly different from that studied previously from a Sharkey soil.

¹ Research paper No. 1136 Journal Series, University of Arkansas, Fayetteville, Ark. Published with the permission of the Director of the Arkansas Agr. Exp. Sta. Presented before Division II, Soil Science Society of America, St. Paul, Minn., Nov. 11, 1954. A major part of this work was submitted by the junior author in a thesis for a partial fulfillment of the requirements for the M.S. Degree in the Graduate School, University of Arkansas. This investigation was largely supported by the Mathieson Chemical Co., Inc., and this support is gratefully acknowledged.

² Associate Professor and former Graduate Assistant, respectively.