Keywords :

Assessing the hydrological impacts of cropping practices in Mediterranean environments

In catchments in which cropland accounts for a major share of the area, cropping practices are an important factor with respect to increasing risks of soil erosion and diffuse pesticide pollution of water. These risks are assessed on two complementary scales, i.e. cropping practice implementation (crop plot) and integration of their effects (catchment).

On the plot scale, studies are carried out to assess the impactof different soil maintenance practices on soil surface states that determine the division between runoff and infiltration of water and associated sediment. A typology of soil surface states based on the structural organization of the soil surface was drawn up. Each described surface state was characterized by soil infiltrability properties. On the basis of this functional typology, the aim was to develop an original approach for temporally continuous modelling of infiltration on plots.

Several soil surface state trajectories were identified on the basis of soil characteristics, climatic events and crop management sequences implemented by wine growers. Experiments carried out on vineyard plots also revealed the effects of several soil maintenance practices (chemical weeding, tillage, natural or sown, permanent or temporary, grass cover) on water transfers, erosion and pesticides.

On a catchment scale, the assessment was based on a distributed hydrological model to simulate water and associated sediment flows according to different cropping practice and climatic scenarios. The spatiotemporal distribution of cropping operations with a hydrological impact (soil maintenance and pesticide treatments) on each plot in the catchment has to be known to be able to apply the model. In the absence of comprehensive data on cropping practices, studies were focused on building a decision model to simulate farmers’ crop management sequences (collaboration with UMR Innovation and the Biometry and Artificial Intelligence unit in Toulouse, France).

For each farm in the catchment, the model is based on a representation of the vineyard annual technical management strategy in the form of activity plans. These plans involve agrosystem status indicators (e.g. grass growth, soil carrying capacity, phenological state of the grapevines) and take into account the characteristics of productive resources on the farm (plot patterns, equipment and manpower) and arbitration between cultivation operations and competing plots.