Modelling the water and nitrogen balance in Intercropping vineyards with cover crop is a key issue for a better prediction of the competition for water and nitrogen between the two species in a variety of climate, soils and vineyards management. APES (Agricultural Production and Externalities Simulator) is a field-scale modular simulation platform for cropping systems, developed within the Seamless project. The simulation of cover cropped vineyards requires the use of Crop, Vineyard, climate, soil and resource arbitration components. This new tool was developed and evaluated on field experiments in southern France and showed promising results to simulate a large range of crop management strategy combining type of intercrop and nitrogen management, under soil-rainfall combinations, on water and nitrogen budget and yield. In the present study, we use both water stress and nitrogen stress indexes to assess competition for water and nitrogen in a vineyard cover cropped with barley under Mediterranean soil and climate.