For decades the main objective of farmers was to get the highest yields from their farmland. Nowadays, quality of agricultural products is becoming more and more important for the largest returns. In addition, the effects on our environment are also becoming important. These put increasing limitations on modern agriculture. So-called site-specific management can optimize the input of, for instance, nutrients and pesticides to the need of the plants. In this study, the objective was to study whether spectral measurements are suitable for determining optimal nitrogen (N) fertilization levels in potatoes. For determining this optimal N level, two field trials were designed in a potato field. Both trials had four N levels in four replicates. Spectral measurements were performed with a CropscanTM 8-band radiometer during the growing season. In addition to the spectral reflectances, the weighted difference vegetation index (WDVI) and the red-edge position (REP) were derived. Results show that WDVI and REP were significantly correlated with tuber yield and can be used for setting optimal N levels. Biomass maps can be created using remote sensing images for mapping relative differences within fields. Based on these maps the farmer can take site specific actions to improve his overall management within a parcel.