Although a priori thinking would suggest that a low intensity crop is environmentally favourable, this assumption ignores the effect of reduced productivity which could simply lead to pollution shifting to other places. A life cycle assessment of the wheat (Triticum aestivum L.) production system for breadmaking was performed to optimise fertilization. In European temperate climate conditions, fertilizing with nitrogen mostly influences the intensity of field production systems, the quality of agricultural products and the environmental degradation. To assess and compare environmentally relevant impacts of different intensities of production, adequate functional units were developed to take into account the main functions of agricultural activity: production and upkeep of agricultural landscape. The limits of these functional units were identified and the influence of the choice of functional unit was analysed.