Interaction of Methabenzathiazuron with Homoionic Soil Clays— II. Desorption Studies

Desorption studies of methabenzathiazuron (MBT) from homoionic clays of three Mollisol soil series showed that most of it occurred in the first desorption cycle and very little MBT was removed in the subsequent ones. In four successive cycles, 26.7 to 52.7% only of the adsorbed MBT could be desorbed indicating its irreversible fixation by the clays. The clays isolated by ultrasonic dispersion retained more MBT than those obtained by citrate buffer dithionite (CBD) treatment at comparable adsorption conditions. Among the cation-clay systems, the extent of desorption was in the order: Al³⁺ > Zn²⁺ > Mg²⁺ > Ca²⁺. Per cent desorpt.on decreased with increase in the level of adsorbed MBT. Considerable hysteresis was observed in all cation-clay systems.