The subject of this thesis was to evaluate the capability of the FEMMA model in simulating the daily nitrogen load from a forested catchment. For that FEMMA was tested in a forest plot in Hyytiälä, Juupajoki. The modeling results of the concentrations of ammonium, nitrate and dissolved organic nitrogen in the runoff water were compared to the measured values of those. This work presents the current state of knowledge concerning the most significant nitrogen processes in forest soil, as reported in the literature. It also lists some alternative models for simulating nitrogen and evaluates the uncertainties in the modelling critically. As a result FEMMA was found not to be suitable for simulating daily nitrogen load from this catchment. The simulated results didn't correspond to the measured values. The most significant factors to develop in FEMMA found in this study were the parametrization of the gaseous nitrogen losses from the system, re-examining the nitrogen uptake by plants and developing the computing of the fractions of nitrogen released in decomposition. For future research it would be important to decide if it is meaningful to simulate the daily nitrogen leaching with process-based models at all. At least in the Hyytiälä site the amount of leached nitrogen is so small compared to the nitrogen in other processes that it's quite challenging to simulate it accurately enough.