SORPTION OF METRIBUZIN AND METOLACHLOR IN ALASKAN SUB-ARCTIC AGRICULTURAL SOILS

Adsorption and desorption of metribuzin and metolachlor were studied for 0- to 15- and 30- to 45-cm soil depths and at 5 and 28 C temperatures for two subarctic Alaskan agricultural soils. Surface soils had five to eight times the organic carbon content of deeper soils and had lower Freundlich isotherm slopes (1/n) for both herbicides. Surface soil Freundlich coefficients (K(f)) were affected by both soil type and equilibration temperature, with soil type accounting for greater than 80% of the variation in K(f). Surface soil mean K(f) values ranged from 1.5 to 2.4 for metribuzin and 4.4 to 9.2 for metolachlor. For soils from the 30- to 45-cm depth, neither soil type nor temperature affected K(f). Isotherm slopes for desorption were less than adsorption, indicating hysteresis. Regressions between desorption K(f) and maximum herbicide adsorbed prior to desorption were highly significant with coefficients of determination (r2) between 0.50 and 0.99. Nomenclature: Metribuzin, 4-amino-6-(1,1-dimethyl-ethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one; metolachlor, 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide.