Mineral nitrogen in agriculture has increased greatly food supply and allowed the historical population growth of the past century. Its intensive use is nevertheless the source of numerous environmental issues and remains a major challenge for policymakers. In this paper, we explore the eects of a public policy aiming at halving mineral nitrogen use over European agriculture. We investigate the impacts in terms of agricultural production, prices, land use change and the resulting consequences for ecosystems and biodiversity. We present a modeling framework that links a set of models covering agronomic, economic, land-based, and biodiversity processes. We propose a comprehensive analysis of the underlying mechanism at play. At the EU level and regarding the results only from agronomic and supply-side models, reducing nitrogen implies lower crop yields, lower prots, and less agricultural land. However, following the results from global scale economic models that take into account market feedbacks, the policy implies an increase in food prices and the substitution of nitrogen input for land. Land allocation is then modied at the global level as the result of a \leakage" of the European scale nitrogen policy.