DETECTION OF SALT TOXICITY AND NITROGEN DEFICIENCY IN CUCUMIS SATIVUS L. USING SPECTRORADIOMETRY AND COLOR INFRARED IMAGERY

Abstract

Spectral changes in Cucumis sativus L. plants caused by sodium chloride (NaCl) toxicity and nitrogen deficiency were evaluated to determine if abiotic stressors were detectable using color infrared (CIR) imagery. Sodium chloride toxicity was manifested by a decrease in reflectance of green and near-infrared (NIR) wavelengths (550 and 825 nm, respectively), which became evident one week post-treatment among plants subjected to high salt concentrations (0.10 and 0.20 M NaCl). The latter exhibited an increase in reflectance of red wavelengths (680 nm), although effects did not become pronounced until the third week post-treatment. In contrast, spectral changes associated with nitrogen deficiency were the most pronounced in the visible wavelengths and varied in the time required for symptom manifestation. 100% nitrogen (N) deficiency symptoms became evident two weeks before those in plants with 50% nitrogen deficiency. Spectral differences were also detectable in CIR images acquired under artificial lighting. Subtle differences among treatments were accentuated using ratio images (NIR/red).