| Abstract: | Isoxaflutole is a new pre-emergence corn herbicide which controls both grass and broadleaf weeds. Experiments were performed in the laboratory to study the sorption of isoxaflutole in five different soils (Moorhead, MN; East Monroe, CO; Ellendale, MN; South Deerfield, MA; and Chelsea, MI) using the batch equilibration technique. Total initial isoxaflutole solution concentrations for each soil were 0.05, 0.15, 0.3. 0.8, 1.5, 2.0 and 4.0 mg litre−1. Analysis of ring-14C] isoxaflutole was performed using liquid scintillation counting, and sorption data were fitted with the Freundlich model. Isotherms of isoxaflutole in all the soils were non-linear as depicted by the exponent (n < 1.0), indicating differential distribution of sorption site energies in various soils. Since the isotherms were non-linear the data fit Freundlich's isotherm well, as was indicated by high values of the regression coefficient (r2). The Freundlich sorption coefficient ranged from 0.555 to 50.0 (litre nmg l−nkg−1). Multiple regression of the sorption constant, KF against selected soil properties indicated that organic matter content was the best single predictor of isoxaflutole sorption (r2 = 0.999) followed by soil pH (r2 = 0.954). Clay content of the soils did not have a high correlation with KF values (r2 = 0.453), while the sorption of isoxaflutole was not influenced by the Ca2+ concentration in the soil solution. Isoxaflutole sorption increased with an increase in organic matter content of soils. Sorption of isoxaflutole decreased as the soil pH increased from 4.5 to 8.5, which was depicted by the reduction of KF values. Sorption of isoxaflutole to the soils varied with differences in binding energies. At a particular net energy value (E*), the corresponding site energy distribution F(E*)] values followed the order, Chelsea, MI > Moorhead, MN > East Monroe, CO > South Deerfield, MA > Ellendale, MN. The negative magnitude of Gibbs free energy of sorption (ΔG x) indicates the spontaneity of the given sorption process in the soils from Moorhead, MN; East Monroe, CO and Chelsea, MI. © 1999 Society of Chemical Industry |
