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Exchange of Diquat²⁺ in Soil Clays, Vermiculite, and Sniectite¹

ABSTRACT

Clay samples were saturated with diquat²⁺ by a centrifuge washing procedure. Exchangeable diquat²⁺ was replaced by washing samples with 1N KCl solutions. Exchange of diquat²⁺ by K⁺ was 23 to 26% complete for three Wyoming montmorillonites and was 35 to 44% for three montmorillonite samples from Alabama and Mississippi. Diquat cations were 59% exchangeable in a nontronite. Diquat cations satisfied 57 and 82% of the cation exchange charge of Texas and Montana vermiculites and K⁺ replaced 98 and 88% of the diquat²⁺, respectively. There was a direct relationship between K⁺-diquat²⁺ exchange and layer charge density (CEC) of the montmorillonites and vermiculites. Hydroxy-Al interlayers had little influence on the exchange of diquat²⁺ in vermiculite and in montmorillonite except where double interlayers were deposited. Eleven soil clays had from 27 to 98% of their cation exchange charge countered by diquat²⁺. The exchangeability of diquat²⁺ in the diverse group of soil clays was directly related to vermiculite content. Montmorillonitic soil clays fixed more diquat²⁺ than vermiculitic soil clays. Diquat²⁺ was about 70% exchangeable in montmorillonitic soil clays which also contained vermiculite and kaolinite. The exchangeability of diquat²⁺ in montmorillonitic Houston and Iredell soil clays and their K⁺ fixing ability on oven drying indicate that vermiculite may have an important influence on their K⁺ exchange reactions.

¹ Contributions from the Dept. of Agronomy and Soils, Agr. Exp. Sta., Auburn Univ., Auburn, Ala. This study was supported in part by Interior's Office of Water Resources Research through the Water Resources Res. Inst. of Auburn Univ. The senior author wishes to acknowledge the support of Texas A&M Univ. Agr. Exp. Sta. during preparation of the manuscript. Presented before Div. S-2, Soil Science Society of America, Nov. 9, 1967, at Washington, D.C.

² Formerly Associate Professor, formerly NASA Graduate Trainee, and Research Assistants, respectively. Professor, Texas A&M Univ. and Research Fellow, Univ. of Wisconsin, for the first two authors.

Received for publication December 1, 1969. Accepted for publication January 6, 1970.