Sorptton‐desorption of herbicides in soil as influenced by electrolyte cations and ionic strength∗

Florida Agricultural Experiment Station Journal Series No. R‐00799.

Abstract

Accurate prediction of pesticide leaching potential and contamination of groundwater required improved understanding of the influence of various soil factors on pesticide sorption/desorption. Effects of varying ionic strength and cation composition of electrolyte on sorption/desorption of bromacil [5‐bromo‐6‐methyl‐3‐(l‐methylpropyl)‐2,4 (1H, 3H) pyrimidinedione], simazine [6‐chloro‐N‐N'‐diethyl‐l,3,5‐triazine‐2,4‐diamine], norflurazon [4‐chloro‐5‐(methyl‐amino)‐2‐(3‐(trifluoromethyl) phenyl)‐3(2H)‐pyridazinone], and diuron| [N'‐(3,4‐dichlorophenyl)‐N,N‐dimethylurea] by a Candler fine sand (0–15 cm; hyperthermic, uncoated Typic Quartsipsamment) were investigated. Among the herbicides used, sorption decreased in the order: diuron > norflurazon > simazine > bromacil. Sorption of all four herbicides increased with increasing ionic strength of the electrolyte. Using 1.0 M CaCl₂ as an electrolyte for equilibration of soil with herbicides increased the sorption of bromacil, simazine, norflurazon, and diuron by 33, 32, 14, and 17%, respectively, as compared to the sorption using 0.01 M CaCl₂. Sorption of all four herbicides showed very little difference when using either CaCl₂ or KC1 as an electrolyte for equilibration at 1.0 M concentration. Sorption of bromacil, simazine, norflurazon and diuron were increased by 25, 27, 21, and 20%, respectively when electrolyte KCl concentration was increased from 1.0 to 2.0 M. Desorption of all four herbicides in 1.0 M NH₄OAc increased significantly as the electrolyte concentration during sorption was increased. The effects of electrolyte cation species on the sorption of herbicides ranked in the following order:

1. Fe >> Al = Cu > K = Ca = Mg = Na for bromacil, simazine, and norflurazon and

2. Fe ≫ Al = Cu > K > Ca = Mg = Na for diuron. Desorption of all four herbicides in 1.0 M NH₄OAc was greater when either Fe, Al, or Cu electrolyte was used during sorption as compared to using basic cations including K, Ca, Mg, or Na electrolytes.

Key words:

• Basic Cations
• Bromacil
• Citrus
• Diuron
• Herbicide Leaching
• Metal Ions
• Norflurazon
• Simazine.

Notes

Florida Agricultural Experiment Station Journal Series No. R‐00799.