Optical reflectance and fluorescence for detecting nitrogen needs in Zea mays L

Nitrogen (N) status in field grown corn (Zea mays L.) was assessed using spectral techniques. Passive airborne hyperspectral reflectance remote sensing, passive leaf level reflectance, and both passive and active leaf level fluorescence sensing methods were tested. Reflectance of leaves could track total Cha levels in the red dip of the spectrum and auxiliary plant pigments of Chb and carotenoids in the yellow/orange/red edge reflectance. Based on leaf level reflectance behavior, a modified chlorophyll absorption reflectance index (MCARI) method was tested with narrow bands from the Airborne Imaging Spectroradiometer for Applications. MCARI indices could detect variations in N levels across field plots. At the leaf level, ratios of fluorescence emissions in the blue, green, red and far-red wavelengths sensed responses that were associated with the plant pigments, and were indicative of energy transfer in the photosynthetic process. Fluorescence emissions of leaves could distinguish N stressed corn from those with optimally applied N. Reflectance and fluorescence methods are sensitive in detecting corn N needs and may be especially powerful in monitoring crop conditions if both types of information can be combined.