"Red edge" optical properties of corn leaves from different nitrogen regimes

High resolution (<2 nm) optical spectra and biophysical measurements were acquired from corn leaves from field plots having four nitrogen fertilizer application rates: 20%, 50%, 100% and 150% of optimal levels. Reflectance (R), transmittance (T), and absorptance (A) spectra were obtained for both adaxial and abaxial leaf surfaces. The strongest relationships between foliar chemistry and optical properties were demonstrated for C/N content and two optical parameters associated with the "red edge inflection point" (REIP): 1) anormalized first derivative maximum (Dmax) occurring between 695 and 730 nm (Dmax/D744); and 2) the wavelength associated with Dmax (WL of REIP). A nonlinear increase in the Dmax/D744 ratio as a function of C/N content was observed for all optical properties (r2 = 0.90-0.95). Similarly, a nonlinear decrease in the WL of REIP as a function of C/N content was observed for all optical properties (RT, RB, TT, and AT) (r2 = 0.85-0.96). The Dmax/D744 ratio increased as the WL of REIP declined from ∼730 to 700 nm, with curves per optical property expressing different degrees of nonlinearity.