In-field assessment of wheat-leaf polyphenolics using the new optical leaf-clip Dualex
In: Precision Agriculture ‘05zoran.cerovic@ese.u-psud.fr
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In addition to the widely known leaf chlorophyll (Chl) detection by absorbance or reflectance, we propose here to use optical assessment of leaf polyphenolics content (Phen) as an indicator of crop nitrogen (N) status. We developed a portable instrument based on chlorophyll fluorescence excitation spectra, the Dualex®, adapted to measurements of leaf Phen content in the field. It operates in full daylight with a UV beam at 375 nm and a red reference beam at 650 nm. Thanks to the use of a patented feedback loop, measurements take less than a second. We used the Dualex® to follow the dynamics of wheat-leaf Phen in fields that had received different N fertilisation rates. We showed that wheat crops under N deficiency accumulate more Phen. Thus, Phen responded in an opposite manner to Chl. We propose the use of the Chl to Phen ratio as an indicator of crop N status. This new indicator is more sensitive than Chl or Phen alone, and alleviates, at least partially, the problem of gradients along wheat leaves. This is an important argument in favour of the implementation of both Chl and Phen measurements to the next generation of active non-contact sensors for real-time site-specific N management.