Solutions are needed to reduce the negative environmental impacts of imprecise nitrogen (N) fertiliser use at different scales, including medium and small-scale production. Proximal and remote sensing information on crop N status has been shown to be valuable for improving N use efficiency at different scales (Raun et al., 2002; Sharma & Bali, 2017). In this study, commonly used sensors and methods are compared on the basis of their accuracy and robustness in assessing crop N in the field. The comparison of spectral information within five different categories of optical sensor platforms reflects market availability for use in both practice and research. The data for the case study were collected in 2019 in two experimental fields in north-eastern Switzerland, cultivated with winter wheat (T. aestivum). The equipment used consisted of a satellite platform, a fixed-wing unmanned aerial vehicle (UAV), a quadcopter UAV, a handheld field spectrometer and a tractor-mounted system. A power regression was used to compare the ground truth data of crop N content collected in the field with several spectral indices such as the Normalised Difference Red Edge (NDRE) (Argento et al. 2022). The main finding of this study was that the information obtained was comparable in quality and performance across different sensor levels and platforms. Thus, we conclude that sensor-based N status determination can contribute to broadly promote the improvement of N use efficiency, regardless of the available technology and sensing level.
