Estimation of wheat water status by reflectance measurements

Water stress, one of the most limiting factors in crop production, is a worldwide problem. Reflectance measurements may provide inexpensive and fast estimates of water status of crops. A pot experiment was conducted in the glasshouse with summer wheat cv. Thasos. Six different water levels were chosen based on the maximum water capacity of the soil and designed as 65%, 52%, 39%, 32.5%, 26% and 19.5% with three replications. Leaf scans of wheat plants were performed with a digital LEICA S1 PRO camera under controlled light conditions. Leaf scans were evaluated with the L*a*b*-color system. This is a three-dimensional system with parameter a* describing the green/red percentage and parameter b* the blue/yellow percentage of a color. L* represents the lightness of a color. The results showed that reflectance parameter a* and/or b* in 9 specific wavelength ranges increased along with the level of water stress. There is a linear correlation between parameter b* in the 9 wavelength ranges. The best correlation was found in the wavelength range of 510～780 nm with r²=0.95. The results indicate that reflectance measurements may provide a powerful tool for the evaluation of water status in wheat plants.