Effect of water condition on hyperspectral and red-edge characteristics of tobacco leaf

Red-edge characteristics of two cultivars of tobacco under different water treatments were analyzed by measuring leaf spectra with ASD Fieldspec HH. The relationship between red-edge parameters and physiological indices of tobacco was also determined. The results showed notable differences between leaf spectral reflectance of the two cultivars under different water treatments. However, the trend of change in spectral reflectance was similar in the two cultivars. While near-infrared band reflectance increased with increasing soil moisture during root elongation and vigorous growth stages, it decreased at mature stage. Leaf spectral reflectance was highest at vigorous growth stage. Though first differential spectra of red-edge of tobacco leaf showed similar tends, first derivative spectra were significantly different under different treatments. Red-edge position shifted from short to long wavelength with decreasing soil moisture, causing red shift during tobacco entire growth period. While the slope and area of red-edge increased at root elongation and vigorous growth stages (characterized as red shift), they shifted from long to short wavelength at mature stage (characterized as blue shift). The correlations of red-edge position with physiological indices of tobacco leaf were more significant than those with red-edge slope and area. There were significant correlations among red-edge position with contents of chlorophyll a, chlorophyll b, chlorophyll a+b and carotenoid; leaf fresh-weight, leaf dry-weight, leaf area and leaf moisture contents. There were also significant positive correlations among red-edge slope and area with chlorophyll a, chlorophyll b, chlorophyll a+b, carotenoid and leaf moisture contents. The correlation between red-edge area and leaf dry-weight was negative.