Determination of Salt Stress by Plant Leaf Temperature and Thermal Imaging in Black Cumin Grown Under Different Salt Sources

Thermal imaging has been used in recent years to determine salinity stress in certain crops. However, no information is available on this regarding black cumin (Nigella sativa L.). The main purpose of this study was to investigate the determinability of the salt stress on black cumin by thermal imaging. The leaf temperature values were obtained by acquiring the thermal images for black cumin grown under different irrigation water salinity levels (0.6 as control, 1.5, 2.5, and 5.0 dS/m) prepared for different salt sources (CaCl2, MgCl2, NaCl, Ca(NO3)(2), MgSO,(4) and Na2SO4). Plant leaf temperatures averaged over all irrigation water salinity levels did not show a significant difference among salt sources. On the other hand, plant leaf temperatures independent of the salt sources significantly increased with increasing salinity levels. The order for salinity levels in terms of their effect on the leaf temperature of black cumin was determined as 5.0 dS/m > 2.5 dS/m > 1.5 dS/m >= 0.6 dS/m. The highest leaf temperature was obtained under 5.0 dS/m salinity level with CaCl2, MgCl2, Ca(NO3)(2), MgSO4, and Na2SO4 salt sources, but the values for MgSO4 and Na2SO4 salt sources were not significantly different from those under 2.5 dS/m salinity. In addition, a strong-negative relationship between plant water consumption and leaf temperature under CaCl2 and MgSO4 and a moderate-negative relationship under MgCl2 and NaCl salt sources were determined. The results of this study showed that the plant leaf temperature values obtained by thermal imaging reflected salt stress conditions, especially under high salinity levels.