Simulation and prediction of dissipation kinetics of two herbicides in different pedo-climatic situations

Simulations of dissipation kinetics of atrazine and sulcotrione in the 0-10 cm soil layer are obtained with three different numerical models: VARLEACH, PRZM and LEACHP. These simulations are compared to observed residual extractable amounts of herbicide at several times. Observations were done during two years in three different pedo-climatic situations: in the Paris Bassin at Grignon, in the polder of the Mont-Saint-Michel Bay (Brittany) and in the south of France at Roujan (Herault). Comparisons were done taking into account the uncertainties associated with both simulations and observations. They show that the quality of simulations is greatly dependent on the soil, the climate, the year of observation and on the model used. Limits for prediction of herbicide dissipation kinetics in the surface soil layer are discussed.