Catchment-scale modeling of pesticide fate in soil, water and air, taking into account intra-field heterogeneity in vineyard contexts.

Vines are a major consumer of pesticides. Pesticide contamination has been reported for all environmental compartments in the wine-growing context, prompting the definition of more sustainable vine-growing methods. Intra-parcel heterogeneity in vineyard plots is high, due to the fact that vines are grown in rows, pesticides are applied mainly to these rows, and several soil management practices coexist within a plot (chemical weeding, tillage, grassing). To evaluate the environmental dispersion and fate of pesticides in vineyards, we have adapted the field plot sub-model of integrative pesticide landscape fate model MIPP (Modélisation Intégrée du devenir des Pesticides dans les Paysages agricoles) (Voltz et al., 2019). MIPP is a spatially explicit mechanistic model that couples the fate of pesticides in soil, water, and air as influenced by the spatial and temporal organization of farming practices and landscape properties. It thus considers the horizontal hydrological and atmospheric transfers within the landscape, using respectively the MHYDAS and FIDES model. The plot-scale sub-model distinguishes between rows and inter-rows compartments so that different management practices can be applied and spraying deposits correctly located. Concerning the processes, the plot-scale sub-model is based on the coupling of the following three sets of modules:

- a mechanistic soil fate module from the VSoil modelling software platform that simulates water, heat and pesticide transfers in dissolved or gaseous form. Physico-chemical equilibrium is assumed between the solid, liquid, gaseous phases in soil. Volatilisation is calculated from the soil and the vine leaves. Pesticide exchange rate between surface run-off water and soil surface layer is assumed proportional to the pesticide concentration gradient.

- a three sources energy balance module explicitly considering the proportions of plot area covered by bare soil, vine canopy and grass cover.

- a module simulating the evolution of surface conditions, which includes the simulation of the dynamics of spontaneous herbaceous cover in inter-row compartments considering water stress and the changes in soil hydraulic conductivity according to soil management.

The MIPP model is developed within the modelling software platform OpenFLUID that enables easy coupling.

This presentation will focus on a description of the model, a first series of performance evaluations and applications to estimate the environmental impact of pesticides in a Mediterranean wine-growing watershed (Rieutort, located in southern France).