This study evaluates whether a process-based agro-hydrological model can reproduce nitrate leaching dynamics across different fertilization intensities when calibrated only with low and recommended nitrogen inputs. Twelve years of lysimeter observations (2009–2021) were combined with DAISY model simulations for a temperate loamy sandy Cambisol in Zürich, Switzerland. The study addresses whether process-based agro-hydrological models calibrated under standard fertilization conditions can reliably extrapolate to higher nitrogen inputs, and what this reveals about model structural limitations. While the model reproduced soil water dynamics and nitrate leaching under low and recommended fertilization levels, it failed to capture the leaching observed under over-fertilization, highlighting a large potential for uncertainty under such conditions.