Non-destructive estimation of water status on intact crop leaves based on spectral reflectance measurements
1993
Inoue, Y. (National Inst. of Agro-Environmental Sciences, Tsukuba, Ibaraki (Japan)) | Morinaga, S. | Shibayama, M.
Visible and near- and mid- infrared spectral measurements were made on intact and detached leaves of four crop species (Corn, Peanut, soybean and Wheat) using two spectroradiometers under three different conditions: field measurements under artificial light and solar radiation conditions with and without an integrating sphere, and laboratory measurements with an integrating sphere. In the regions of 1350-1480, 1800-2000. and 2350-2500 nm wavelengths, measurements of spectral reflectance (rho) of crop leaves were not possible, even under fully sun-lit conditions due to atmospheric absorption of light in these regions. Relative water content RWC, %) was well correlated with ln (rho-1910), rho-1430, and ln (rho-1650), while water content (WC, H2O mg cm (-2)) was correlated with rho-1200/rho1430, rho-1650/rho-1430, rho-800 - rho-1200 and rho-1100 - rho-1200. Despite very high correlation between those indices and RWC for different crops, no common regression equation was obtained. On the other hand, a common linear relationship was obtained between spectral induced and WC for all four crops irrespective of leaf thickness, chlorophyll content and structure. The first derivative at 1121 nm was also found to be closely related to leaf water status. An obvious spectral shift of inflection point associated with water status was found around 2010 nm region. The location of inflection point shifted over a range from 2080 to 1880 nm according to the dehydration of leaves, and the degree of the shift was closely correlated with RWC and WC. Relative leaf water status of intact leaves of drought-stressed and well-watered soybean plants was estimated from spectral measurements in the field
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