The variation in the availability of diuron to transport by overland flow w
as studied in a vineyard field under a Mediterranean climate during three y
ears. The availability of diuron decreased with time due to the dissipation
of diuron in the topsoil and the decrease of its accessibility by runoff w
ater, which is not represented in pesticide transfer modelling. Thus, calcu
lated concentrations of diuron with simple and actual relations are always
greater than those measured in the overland flow. (C) 2000 AcadCmie des sci
ences/ Editions scientifiques et medicales Elsevier SAS.