Page 5 - Modelisation du devenir des pesticides...

Pesticide fate modelling in soils with

a crop model: model evaluation at

long term

Abstract

A pesticide fate module was implemented in the crop model STICS (Simula-
teur mulTIdisciplinaire pour les Cultures Standard) in order to simulate pesticide
transfer in agricultural soils. Then the model has been evaluated with three study
sites datasets. Pesticide fate modelling is assumed to be a relevant approach to
study pesticide dissipation at the catchment scale. Simulations of four herbicides
(atrazine, simazine,isoproturon chlortoluron) and one metabolite (DEA) were car-
ried out with the crop model STICS over a 23-year period (1990-2012). The model
application was performed with two crops wheat and maïze using real agricultural
practices extracted from the database APOCA (Agricultural Practices of the Or-
geval Catchment Area).
The objectives of the study were i) to highlight the main processes implied in
pesticide fate and transfer at long-term; ii) to assess the influence of the dynamics
of the remaining mass of pesticide in soil on transfer; iii) to determine the most
sensitive parameters related to pesticide losses by leaching over a 23-year period.
The simulated data related to crop yield, water transfer, nitrates and pesticide
concentrations were first compared to observations over the 23-year period, when
measurements were available at the catchment scale. Then, the evaluation of the
main processes related to pesticide fate and transfer was performed using long-term
simulations at a yearly time step and monthly average variations. Analyses of the
monthly average variations were oriented on the impact of pesticide application,
water transfer and pesticide transformation on pesticide leaching. The evolution
of the remaining mass of pesticide in soil, including the mobile phase (the liquid
phase) and non-mobile (adsorbed at equilibrium and non-equilibrium), was studied
to evaluate the impact of pesticide stored in soil on the fraction available for

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