Environmentally sound slurry application requires the accurate estimation of crop N availability. This is hampered by insufficient knowledge about the N mineralization after long-term slurry applications. Therefore, the residual N effect often is not considered explicitly, and N fertilizer value and N budgets are underestimated. Appropriate models may support the analysis of long-term effects, where experimental tools fail. The aim of this study was to quantify the residual N effect of cattle slurry in silage maize using the mechanistic SPN model. Model calibration was based on a 5-year field experiment (1997-2001) conducted on a sandy soil in Northern Germany. Nitrogen fertilization treatments comprised three cattle slurry fertilisation rates (0, 20, 40 m3 ha-1) combined with four mineral N rates (0, 50, 100, 150 kg N ha-1). Maize yield and N content were recorded fortnightly throughout the growing season. Soil mineral N (0-90 cm) was measured in the spring and autumn, leaching losses were estimated by ceramic cups. The SPN model was used to simulate the N dynamics in the soil-crop system. Results of a 5-year simulation were compared with field data, and a 36-year simulation (1966 to 2001) was conducted to quantify the residual N effect and corresponding N balances. Periods of 3 to 9 years with manure application were interrupted by periods without application, and the predicted plant N-uptake was compared to that predicted for crops receiving mineral fertiliser only. Three year application with approximately 30 m³ ha-1 y-1 (100 kg N ha-1 y-1, 50 % as ammonium) plus 50 kg mineral N ha-1 y-1 increased the crop N-uptake in the following 3 years by about 30 kg N ha-1 (i.e. 20 % of the organic N in the applied manure) compared to mineral fertilisation only. Consequences for N fertilizer value assessment and N budgets are discussed.