Fate of soil applied herbicides : Experimental data and prediction of dissipation kinetics

Dissipation kinetics of several soil-applied herbicides [atrazine (6-chloro-2 ethylamino-4 isopropyl-1,3,5-triazine-2,4 diamine), simazine (6-chloro-2,4-diethyl-1,3,5-triazine-2,4-diamine), diuron (3-(3,4-dichloro-phenyl)-1,1-dimethylurea), and sulcotrione (2-(2-chloro-4-mesyl-benzoyl)cyclohexane-1,3-dione)] are studied at three sites having different climatic, pedological, and agronomical characteristics. Field data were obtained during 2 yr, 1993 and 1994. Information was completed by laboratory measurements of adsorption, desorption, and disappearance kinetics obtained at two temperatures (15 and 28°C) and two soil water contents (50 and 90% soil water capacity). Adsorption and desorption conform to the Freundlich description, sulcotrione being the less adsorbed. Laboratory disappearance kinetics can be approximately described with a first-order law under some conditions. Calculated laboratory disappearance rate coefficients are used to simulate field dissipation kinetics in the 0- to 10-cm soil layer, taking into account the effects of soil temperature (Arrhenius formula) and water content (Walker relation). Observed field dissipation kinetics, which are not fully described by a first-order law, can be approximately simulated. Results are discussed from the points of view of agronomy and environment.