Foliar reflectance and fluorescence responses for plants under nitrogen stress determined with active and passive systems

Leaves of corn (Zea mays L.) and soybean (Glycine max L.) plants were examined in a set of four experiments conducted in the summer of 2001 at USDA in Beltsville, MD. Red edge reflectance spectra and red (R) and far-red (FR) fluorescence emissions were acquired for adaxial and abaxial leaf surfaces, in conjunction with foliar chlorophyll content, photosynthetic capacity (Amax), and C/N ratio. A red edge first derivative ratio was strongly related to chlorophyll content, Amax, and C/N ratio. R/FR fluorescence emission ratios also were related to Amax and C/N levels, and enabled species discrimination.