title: Characterization of nitrogen and water status in oat leaves using optical sensing approach.
abstract: 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 (R(2) = 0.90) and heading (R(2) = 0.86) stages across water treatments. Leaf N also had a stronger association with the red-edge position (REP) at both stages (R(2) = 0.83 and 0.78), or with the ratio R4 (R760/R550) at jointing (R(2) = 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Agronomy College, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia, 010019, China; College of Agronomy and Biotechnology, China Agricultural University, Beijing, 100094, China; Agriculture and Agri-Food Canada (AAFC), Science and Technology Branch, Eastern Cereal and Oilseed Research Centre (ECORC), Ottawa, ON, Canada, K1A 0C6.
authors.forename: Baoping
authors.initials: B
authors.lastname: Zhao
authors.forename: Bao-Luo
authors.initials: BL
authors.lastname: Ma
authors.forename: Yuegao
authors.initials: Y
authors.lastname: Hu
authors.forename: Jinghui
authors.initials: J
authors.lastname: Liu
mesh_terms: D018554:Avena / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D055864:Droughts; D008027:Light; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism*; D058998:Remote Sensing Technology; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water; D002734:Chlorophyll; D009584:Nitrogen
keywords: Avena sativa; nitrogen; optical sensing; spectral index; water stress