Nitrogen (N) is the most important macronutrient in plant production. For N application, legislation requirements have raised, and the purchasing costs have increased. Modern sensors can help farmers to save costs, to apply the right quantity, and to reduce their impact on the environment. Two spectrometers and one fluorescence sensor have been used on a vehicle sensor platform for N detection in wheat (Triticum aestivum
L.) field trials over three years. The research fields were divided into plots, and the N input ranged from 60 to 180 kg N ha−1
in six levels. The OSAVI (optimized soil-adjusted vegetation index) showed a similar value pattern to the NDVI (normalized difference vegetation index) and the CropSpec index for the investigated factors. The red-edge inflection point (REIP) index showed high correlations to N (indicated by r2
between 0.6 and 0.8), especially in June and July. The developed models from the fluorescence indices FERARI, NBIR, FLAV, and the spectrometer indices CropSpec and HVI show high correlations (r2
= 0.5–0.8) to yield and may be used for future yield predictions. The Multiplex Research™ fluorescence sensor (Force-A, Orsay, France) was the most convenient sensor with a simple measurement method and a non-proprietary file output. The implementation into existing agricultural vehicle networks is still necessary, being able to use it on a farm for online N recommendations.
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