Sorption of the Herbicides Isoxaben and Oryzalin to Soils and Container Media

Abstract

Abstract The herbicides isoxaben (Gallery) and oryzalin (Surflan) are commonly used to prevent weed emergence around ornamental plants in nurseries and landscapes. Saturated batch experiments were conducted in the laboratory to generate equilibrium sorption isotherms for these herbicides in soils and container media. Soils consisted of [A] a sandy loam containing 1.24% organic matter (by wt) after sieving, and [B] a silt loam containing 1.36% organic matter (by wt) after sieving. Container media obtained from nurseries consisted of [C] a mixture of 50% peat and 50% sand (by vol) containing 18.5% organic matter (by wt) after sieving, and [D] a mixture of 70% bark, 25% peat, and 5% fine stone (by vol) containing 34.9% organic matter (by wt) after sieving. Sorption isotherms were generated from these data. Based on sorption coefficients (Kd, Kf), container mix D sorbed both herbicides to a much greater extent than did the other substrates. Oryzalin sorption was greater than isoxaben sorption in each soil and container mix. For oryzalin, organic carbon partition coefficient (Koc) values in the soils were greater than those in the container mixes. Compositional differences in organic matter between soils and container media may account for differences in herbicide sorption in these media.