Characterization of nitrogen and water status in oat leaves using optical sensing approach.
Zhao, B., Ma, B.-L., Hu, Y.G., and Liu, J.H. (2015). "Characterization of nitrogen and water status in oat leaves using optical sensing approach.", Journal of the Science of Food and Agriculture, 95(2), pp. 367-378. doi : 10.1002/jsfa.6729 Access to full text
BACKGROUND Optical sensing is a potential tool to estimate plant N status, but soil water deficits may interefere with forming a clear relationship. A greenhouse study was conducted with oat plants treated with three water regimes and four N levels to determine whether optical sensing could be used to estimate leaf N and relative water content (RWC). RESULTS Leaf N was strongly correlated with reflectance at 550 nm and at around 705 nm, and N treatments caused a red-edge peak shift to lower wavelength. The ratio of the first derivative reflectance at 741–696 nm (FDRE) was identified to be a good estimator of leaf N at jointing (R2 = 0.90) and heading (R2 = 0.86) stages across water treatments. Leaf N also had a stronger association with the red-edge position (REP) at both stages (R2 = 0.83 and 0.78), or with the ratio R4 (R760/R550) at jointing (R2 = 0.88), than with chlorophyll meter (SPAD) readings. Under water stress, the predictive accuracy of leaf N increased with these reflectance indices, but decreased using SPAD readings. CONCLUSION The results indicate that specific reflectance indices of FDRE, REP and R4 may be used for a rapid and non-destructive estimation of oat plant N status over a range of water regimes
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