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

Abstract

AbstractClay 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.