RED EDGE STRUCTURE OF CANOPY REFLECTANCE SPECTRA OF TRITICALE

Reflectance spectra at the boundary between the visible and near-infrared reflectance in the domain of the so-called ''red edge' (660-770 nm) were examined over triticale canopy in a two-factor field experiment. The objective was to study changes in the red edge position and shape as a function of developmental stage, cultivar, and plant density. The experimental design involved six cultivars and three plant densities with three replications. Eight spectrometric measurements with 10-nm steps were taken from the moment of breaking winter dormancy until soft dough stage at approximately 2-week intervals. Numerical differentiation of spectra (preapproximated by a cubic spline function) was used to locate the red edge. Three components corresponding to maxima in the rate of increase in reflectance have been resolved in the curve of the first derivative on the average at 700 nm, 715 nm, and 745 nm. The features of the components showed no dependence on the cultivar and sowing rate but varied with plant maturation. At the vegetative stage, the first two components moved to longer wavelengths (a shift of about 5 nm), at the reproductive stage to shorter ones. The peak at 745 nm showed the opposite direction Of movement: from 746-747 nm in early season to 743 nm at heading and towards the longer wavelengths by the late season. Throughout the growing season this peak continued to be the highest one. The results have confirmed that the red edge of the vegetation reflectance spectrum is a complex contour composed of a number of components the peakedness and relative positions Of which vary according to the plant growth stage.