Monitoring corn nitrogen nutrition index from optical and synthetic aperture radar satellite data and soil available nitrogen

Nitrogen (N) nutrition index (NNI) is a reliable indicator of plant N status for field crops, but its determination is both labor- and cost-intensive. The utilization of remote sensing approaches for monitoring N, mainly in relevant crops such as of corn ( Zea mays L. ), will be critical for enhancing effective use of this nutrient. Therefore, the aim of this study was to assess NNI predicted from optical and C-band Synthetic Aperture Radar (C-SAR) satellite data and available soil N (N av ) at different vegetative growth stages for corn crop. Eleven field studies were conducted in the Pampas region (Argentina), applying five fertilizer N rates (0, 60, 120, 180, and 240 kg N ha −1 ), all at sowing time. Plant samples were collected at sixth-leaf (V 6 ), tenth-leaf (V 10 ), fourteen-leaf (V 14 ), and flowering (R 1 ). Using linear regression models, NNI was best predicted using only optical satellite data from V 6 to V 14 , and integrating optical with C-SAR plus N av at R 1 . The best monitoring model integrated vegetation spectral indices, C-SAR and N av data at V 10 with an adjusted R 2 of 0.75 achieved during calibration in the northern Pampa. During validation, it predicted NNI with an RMSE of 0.14 and a MAPE of 12% in the southeastern Pampa. The red-edge spectrum and Local Incidence Angle of C-SAR were necessary to monitor the corn N status via prediction of NNI. Thus, this study provided empirical models to remotely sensed corn N status within fields during vegetative period, serving as a foundational data for guiding future N management.