EFFECT OF SOIL-PH ON ADSORPTION AND PERSISTENCE OF IMAZAQUIN

Laboratory and field studies were conducted in 1988 through 1990 to determine the effect of soil pH on imazaquin adsorption and persistence in a Crosby silt loam (1.6% organic matter) and a Hoytville clay (3.3% organic matter). Above a pH of 6, 6 to 7% of the total imazaquin present was adsorbed to both soils. Adsorption increased as pH decreased from about 7 to 4.5, with a maximum of 16.5 and 31% adsorbed on Crosby and Hoytville soils, respectively. Imazaquin was more persistent in the Hoytville clay than in the Crosby silt loam. Herbicide dissipated more slowly in both soils in 1988 than in 1989 due to dry soil conditions immediately prior to and following herbicide application in 1988. In both soils, imazaquin persistence increased as soil pH decreased, over a pH range from 6.5 to 4.5. Increased persistence with decreasing pH was attributed in part to increased adsorption and decreased availability for microbial degradation.