DISTINGUISHING NITROGEN-FERTILIZATION LEVELS IN-FIELD CORN (ZEA-MAYS L) WITH ACTIVELY INDUCED FLUORESCENCE AND PASSIVE REFLECTANCE MEASUREMENTS

Laser-induced fluorescence (LIF) is an active sensing technique capable of capturing immediate and specific indications of changes in plant physiology and metabolism as they relate to the concentration and photosynthetic activity of the plant pigments. Reflectance is a passive sensing technique that can capture differences in the concentration of the primary plant pigments. Fluorescence and reflectance were compared for their ability to measure levels of plant stress that are of agronomic importance in corn (Zea mays L.) crops. Laboratory LIF and reflectance spectra were made on excised leaves from field grown corn. Changes in the visible region of the spectrum were compared between groups of plants fertilized with seven different levels of nitrogen (N) fertilization. A pulsed nitrogen laser emitting photons at a wavelength of 337 nm was used as a fluorescence excitation source. Differences in maximum intensity of fluorescence occurred at 440 nm, 525 nm, 685 nm, and 740 nm. Significant separations were found between levels of N fertilization at several LIF wavelength ratios. Several reflectance algorithms also produced significant separations between certain levels of N fertilization.