A comparison of multiwavelength laser-induced fluorescence parameters for the remote sensing of nitrogen stress in field-cultivated corn

The capacity of fluorescence induced from several laser excitation wavelengths for the remote detection of nitrogen (N) status of corn was evaluated. Four nitrogen fertilization treatments (unfertilized, uniformly fertilized, fertilized according to chlorophyll status, and saturated) were established in four adjacent fields. Spectral measurements and evaluation of plant parameters were performed two times during the season. Fluorescence emission spectra at five excitation wavelengths (308, 360, 440, 480, and 630 nrn) provided as many fluorescence signatures of the vegetation from which several parameters were derived for their potential in the evaluation of crop nitrogen status. The fluorescence ratios red to far-red (RF/FRF) and blue to far-red (BF/FRF), the fluorescence excitation ratio (FER), and the dual excitation ratio (DER) were computed from different excitation wavelengths. The most sensitive and consistent parameter in discriminating N treatments in both measurement campaigns was FER (FR-FER360/440), which is likely affected by changes in epidermal ultraviolet (UV) transmittance of leaves in relation to nitrogen availability.