To avoid environment pollution and to minimize the costs of using mineral fertilizers an efficient fertilization system, tailored to the plant needs becomes more and more important. For that, the essential information can be determined by detecting certain crop parameters, like dry matter of the plant biomass above ground, N-content and N-uptake. By using fluorescence and reflectance measurements of the canopy and the mathematical analysis these parameters are appreciable.

In three years, 2007 to 2009, two different plot trials in winter wheat were conducted. The first trial consisted of seven different cultivars of winter wheat and four N-rates (0, 100, 160 and 220 kg N/ha). The second trial consisted of only one cultivar with eight N-rates from 0 up to 260 kg N/ha. Each trial was conducted as double plot trial with four replications. One plot was for non-conducting sensor measurements and harvesting with the plot combine, the other plot was for biomass sampling during the vegetation period. Biomass samples for nitrogen analysis and sensor measurements were conducted five times during the vegetation period.

The N-uptake of different growth stages of winter wheat was well represented by using fluorescence and reflectance measurements. Especially the vegetation index REP (Red Edge Point) was therefore adequate, because of the high coefficient of determination to the N-uptake. Another aspect for using the REP was that the influence of the different cultivars was minimized. The coefficient of determination was obviously lower by using the NDVI in comparison to the other vegetation indices. Especially in with N well provided canopies a saturation effect could be observed. By using other spectral areas in the red- and near-infrared wavelength range, combined with the NDVI-formula, the results are different. With this combination the saturation effect almost disappeared and the coefficient of determination between NDVI and crop parameters increased considerably.