Sorption and Mobility of ¹⁴C-Labeled Imazaquin and Metolachlor in Four Soils As Influenced by Soil Properties

Abstract

Aqueous batch-type sorption-desorption studies and soil column leaching studies were conducted to determine the influence of soil properties, soil and suspension pH, and ionic concentration on the retention, release, and mobility of [14C]imazaquin in Cape Fear sandy clay loam, Norfolk loamy sand, Rion sandy loam, and Webster clay loam. Sorption of [14C]metolachlor was also included as a reference standard. L-type sorption isotherms, which were well described by the Freundlich equation, were observed for both compounds on all soils. Metolachlor was sorbed to soils in amounts 2-8 times that of imazaquin, and retention of both herbicides was related to soil organic matter (OM) and humic matter (HM) contents and to herbicide concentration. Metolachlor retention was also related to soil clay content. Imazaquin sorption to one soil (Cape Fear) increased as concentration increased and as suspension pH decreased, with maximum sorption occurring in the vicinity of pK(a1) = (1.8). At pH levels below pK(a1) imazaquin sorption decreased as hydronium ions (H3O+) increased and competed for sites. NaCl was more effective than water in desorption of imazaquin at pH levels near the pK(a1). Mechanisms of bonding are postulated and discussed. The mobility of imazaquin through soil columns was in the order Rion > or = Norfolk > Cape Fear > or = Webster, whereas for metolachlor it was Rion > or = Norfolk >> Webster > or = Cape Fear. Imazaquin was from 2 to 10 times as mobile as metolachlor.

Residual Herbicide Dissipation in Vegetable Production

“…S-metolachlor dissipation was rapid for bare soil and soil under low density polyethylene mulch dropping to undetectable levels by 44 days after treatment. Rapid dissipation has been previously noted for metolachlor with sandy soil under moist soil conditions (Weber et al, 2003). In one experiment, S-metolachlor dissipation was biphasic, dropping to less than 400 ug/kg of soil at 7 days after treatment, yet was detectable at 44 days after treatment for both soil scenarios.…”

“…Metolachlor mobility was inversely related to soil organic matter and clay content. Other studies came to the same conclusions and also indicated that metolachlor binding was by physical forces between metolachlor molecules and soil constituent surfaces (Weber et al, 2003). Half-life of metolachlor varies with soil temperature, moisture, and organic matter content (Parker et al, 2005;Vencill, 2002 a).…”

“…Carpenter et al (1999) reported a positive relationship between organic matter and halosulfuron adsorption, that sorghum [Sorghum bicolor (L.) Moench] injury was less likely on soils with high organic matter content, and halosulfuron can exhibit soil hysteresis. Metolachlor dissipation from soil has been extensively investigated (Bouchard et al, 1982;Braverman et al, 1986;Gaynor et al, 1993;Obrigawitch et al, 1981;Peter & Weber, 1985;Weber et al, 2003). Weber et al (2003) reported that metolachlor sorption, mobility, and soil retention was related to organic matter, clay content, and surface area.…”

“…Metolachlor dissipation from soil has been extensively investigated (Bouchard et al, 1982;Braverman et al, 1986;Gaynor et al, 1993;Obrigawitch et al, 1981;Peter & Weber, 1985;Weber et al, 2003). Weber et al (2003) reported that metolachlor sorption, mobility, and soil retention was related to organic matter, clay content, and surface area. As soil organic matter concentration increases, adsorption of metolachlor increases.…”

“…The residual effects of sulfentrazone on rotational cotton have been established with rates exceeding 0.4 kg ha -1 applied the previous year (Main et al, 2004;Ohmes et al, 2000). Persistence, dissipation, and degradation of halosulfuron (Kuwatsuka & Yamamoto 1997a, metolachlor (Gaynor et al, 1993, Parker et al 2005Weber et al, 2003), and sulfentrazone (Grey et al, , 2000Ohmes et al, 2000;Reddy & Locke, 1998) have been previously investigated in agronomic and/or vegetable soils. These investigations emphasized soil and/or organic cover scenarios in separate experiments.…”