Sorption of Metribuzin and Metolachlor in Alaskan Subarctic 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 (r 2 ) between 0.50 and 0.99.