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 degrees 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.