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).

Keywords:

• spectroradiometry
• color infrared (CIR) imagery
• cucumber (Cucumis sativus)
• salt toxicity
• nitrogen deficiency

ACKNOWLEDGMENTS

This paper is Contribution No. 10-357-J from Kansas Agricultural Experiment Station, Manhattan, Kansas.

Notes

^aValues within columns for each weekly sampling occasion that are followed by the same letter do not differ significantly (P < 0.05), according to Tukey's honestly significant difference (HSD) test. Each value is the mean of fifteen replicated measurements from four leaves of four plants within each treated set.

^aValues within columns followed by the same letter do not differ significantly (P < 0.05), according to Tukey's honestly significant difference (HSD) test.

FIGURE 1 Conventional (RGB) images of C. sativus plants exposed to NaCl under artificial (halogen) lighting (A, D, G), CIR color composite (B, E, H), and NIR/red ratio images (C, F, I). Ratio images (C, F, I) have been contrast stretched at < 1.30, < 1.36, and < 1.14, respectively. Images were obtained at 1 (A, B, C), 2 (D, E, F), and 3 (G, H, I) weeks post-treatment. Treatments are arranged as follows: upper right (0.0 M NaCl [dsH₂O]), lower right (0.03 M NaCl), upper left (0.10 M NaCl), and lower left (0.20 M NaCl)

^aNitrogen was added in the form of ammonium nitrate (NH₄NO₃).

^bValues within columns for each weekly sampling occasion followed by the same letter do not differ significantly (P < 0.05), according to Tukey's honestly significant difference (HSD) test. Each value is the mean of ten replicate canopy measurements for a set of seven plants.

^aNitrogen was added in the form of ammonium nitrate (NH₄NO₃).

FIGURE 2 Conventional (RGB) images of C. sativus plants exposed to nitrogen deficiency treatments under artificial (halogen) lighting (A, D, G), CIR color composite (B, E, H), and NIR/red ratio (C, F, I). Images were obtained prior to treatment (A, B, C) and at 3 (D, E, F) and 6 (G, H, I) wks post-treatment. Plants are arranged as follows: four sets of pre-treatment control (1.0 N) plants (A, B, C); right column (control, 1.0 N), center column (0.5 N), and left column (0.0 N) (D, E, F); upper left (control, 1.0 N), upper middle (0.5 N), upper right (0.0 N), middle left (0.0 N), center (control, 1.0 N), middle right (0.5 N), lower left (0.0 N), lower middle (0.5 N), and lower right (control, 1.0 N) (G, H, I). Nitrogen was added in the form of ammonium nitrate, where control (1.0 N) treatments were 240 mg L⁻¹ of NH₄NO₃

^bValues within columns followed by the same letter do not differ significantly (P < 0.05), according to Tukey's honestly significant difference (HSD) test.