Abstract
It is vital not to under evaluate the adsorption rates of paddy herbicides, which influence their movement in the soil and water for environmental safety and agricultural practice. The adsorption rates of four herbicides, esprocarb, thiobencarb, pretilachlor and simetryn, in three kinds of paddy soil whose properties varied widely were investigated. It was found that the herbicides were absorbed in the soils in two steps characterized by fast and slow phases. The ratios of the fast adsorption α were independent of the initial concentration for each tested system of herbicide and soil. Then an adsorption rate equation was introduced from α and the approximated Boyd equation and its applicability was confirmed. The rate parameters of the slow adsorption Di′/r2 were obtained in the range of 3.4×10-7 to 7.3×10-7/s by the proposed equation. The differences among the herbicides and the soils were small.
