Interaction of Methabenzathiazuron with Homoionic Soil Clays— I. Adsorption Studies

Adsorption of methabenzathiazuron (MBT), the active ingredient of Tribunil (herbicide), on homoionic soil days saturated with a single cation viz, Al³⁺, Zn²⁺, Mg²⁺ and Ca²⁺ was studied. The clays which were separated from soils (Mollisols) by citrate buffer dithionite treatment, showed less adsorption than those obtained by ultrasonic dispersion. The adsorption equilibrium was attained within 24 h in each case. As much as 38 to 80% of added MBT was adsorbed. The clays separated from Phoolbagh soil series showed more adsorption than those of Nagla and Pather-chatta series the amount of MBT adsorbed by clays decreased in the order: Al³⁺>Zn²⁺>Mg²⁺>Ca²⁺ —saturation. Except for the initial concentration below 80 µM/g clay, the adsorption data fitted well into Langmuir equation. A wide variation in the values of equilibrium constant (k) and maximum adsorption (s) was observed, thereby suggesting differences in the mode of binding of the herbicide to the homoionic soil clays.