Diquat binds readily to clay particles in the soil. The rate of adsorption depends on the degree of contact of diquat with adsorbent minerals, the type of soil, and the initial herbicide concentrations tested. Weber et al. (1965) studied the effects of temperature and exposure time on diquat adsorption by montmorillonite, kaolinite, charcoal, and an anionexchange resin in pH 6.0 phosphate buffer. Diquat was preferably adsorbed on the clay particles by a process of ion exchange. Adsorption was limited by the cation-exchange capacity of the test systems examined. Coats et al. (1966) showed the adsorption capacity of kaolinite to be about 2 g/kg and that of bentonite 80 - 100 g/kg.