The assessment of N leaching from agricultural source is important to environment impact studies. In this research have been compared the effects of organic N fertilizers on crop productivity and N leaching in a maize (Zea mays L.) – triticale (x triticosecale WittMack) - maize rotation in the Nitrates Vulnerable Zone of Arborea (Sardinia), using crop simulations models. The DSSAT and SALUS models long term seasonal and rotational simulations, were carried out to evaluate the effects of manure and slurry application on soil N and N leaching for the study period (2007-2008) and for a long term (50 years) weather record and to determine the management strategies that reduce the risk of nitrates contamination maintaining a sustainable production. The simulation results show that inappropriate agronomic management strategies, even when the initial soil N content is low, could allow to reach extremely high values of soil N content and N leaching. Irrigation volumes and scheduling based on the plant extractable soil water and a N fertilization based on crops uptake made possible to reach an adequate biomass production reducing significantly the N leached into the soil profile, even when organic fertilizers are used. Simulation models can support the selection of management options that allow to decrease environmental pollution and the use of improper amount of management inputs and consequently to achieve an ecological improvement for the ecosystem and an economical return.