In order to optimize nitrogen fertilisation, it is necessary to take account both of nitrogen uptake and of nitrogen redistribution within the plant. Quantitative mathematical models of N uptake and partitioning have therefore been developed. The nitrogen uptake model describes uptake by peach trees during the first year of growth, in sand culture with continuous irrigation and N fertilisation. Various candidate models were considered. In this case, the selected model used a third-order polynomial to describe root uptake efficiency. The partitioning model was developed using the same data set. The model describes nitrogen partitioning using a set of differential equations with transport coefficients. N uptake as calculated from the uptake model provides the input of N. The transport coefficients were estimated by fitting the model to the amounts of N in each plant compartment at each measured date. Given these two models, it is possible to calculate nitrogen fertilisation strategy to optimize various objective functions. The present contribution focuses on this use of the models.