The ISOP Project (Prairies Information and Objective Survey) aims to assess in real time the grassland yield variability for 200 geographical areas in France. It uses daily meteorological data interpolated at each area centroid and also soil characteristics and percentages. Cultural practices information, obtained through a national survey, is also introduced. A crop model (STICS) is then applied to assess the grassland yield for each configuration (about 6,000 simulations foreseen in all). At the end, the results are compared to the statistics and aggregated at different spatial scales to be provided to the French Agriculture Ministry.