Calibration of Crop Nitrogen Monitoring Using Ion-Selective Electrodes and Remote Sensing Indices in Horticultural Crops

Accurate monitoring of crop nitrogen status is essential to optimize fertilization management and reduce nitrate losses in intensive horticultural systems. This study aimed to calibrate crop monitoring tools based on ion-selective electrodes and remote sensing indices for nitrogen status assessment in horticultural crops.

Field experiments were conducted during the 2025 growing season on broccoli and watermelon grown under Mediterranean conditions and subjected to different nitrogen fertilization levels. Crop nitrogen status was assessed using complementary approaches. Multispectral satellite imagery and UAV-based hyperspectral data were used to calculate vegetation indices related to chlorophyll and nitrogen status, including NDRE, GNDVI, TCARI and OSAVI. These indices were calibrated against leaf nitrogen concentration and nitrate content determined by conventional laboratory analyses. In parallel, xylem sap was extracted from leaves and analyzed using ion-selective electrodes to determine nitrate concentration.

Strong relationships were observed between nitrogen supply, spectral indices and nitrate concentration in xylem sap, enabling the development of calibration models for real-time crop nitrogen monitoring. The integration of proximal sensing with remote sensing improved the robustness of nitrogen diagnostics across crops and growth stages.

These results highlight the potential of combining ion-selective electrodes and remote sensing tools as decision-support systems for optimized nitrogen management.