Sorption and Mobility of Sulfometuron and Imazapyr in Five Alabama Soils

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Abstract
Mobility and sorption of radiolabeled sulfometuron {2-[[[[(4,6-dimethyl-2-pyrimidinyl)amino] carbonyl] amino] sulfonyl] benzoic acid} and imazapyr {(±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridinecarboxylic acid} were evaluated in five soils representative of the major soil types in Alabama. Thin-layer soil chromatography indicated that sulfometuron was slightly more mobile (average Rf = 0.86) than imazapyr (average Rf = 0.79). Sulfometuron was more subject to sorption (average kd = 0.29) than imazapyr (average kd = 0.09) in batch equilibrium experiments. Least sorption of both herbicides occurred on clay soils, and maximum sorption occurred on a sandy clay. Similar results were obtained with a soil solution recovery technique. Sorption of both herbicides was exhanced by temporary reduction in soil water content and by lowering soil pH. The pH response of imazapyr was greater than that of sulfometuron.