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 capabl e of capturing immediate and specific indications of changes in plant physiology and metabolism as they relate to the concentration and phot osynthetic activity of the plant pigments. Reflectance is a passive se nsing technique that can capture differences in the concentration of t he primary plant pigments. Fluorescence and reflectance were compared for their ability to measure levels of plant stress that are of agrono mic importance in corn (Zea mays L.) crops. Laboratory LIF and reflect ance spectra were made on excised leaves from field grown corn. Change s in the visible region of the spectrum were compared between groups o f plants fertilized with seven different levels of nitrogen (N) fertil ization. A pulsed nitrogen laser emitting photons at a wavelength of 3 37 nm was used as a fluorescence excitation source. Differences in max imum intensity of fluorescence occurred at 440 nm, 525 nm, 685 nm, and 740 nm. Significant separations were found between levels of N fertil ization at several LIF wavelength ratios. Several reflectance algorith ms also produced significant separations between certain levels of N f ertilization.