301 
Greenhouse grown soybean 
leaves were used for the leaf 
level reflectance measurements. 
The plants were grown in perlite 
with varying nitrogen nutrient 
solutions applied (0 % to 100 % 
of optimal growth rate). These 
varying nitrogen concentrations 
produced a range of nitrogen 
deficiency stress that resulted in 
a wide range of leaf pigment 
concentrations and a range of 
reflectance spectra (Fig. 3 (I)). 
Reflectance measurements of 50 
leaves were acquired with a LI- 
COR1800 spectroradiometer and 
integrating sphere (LI-COR, Inc. 
Lincoln, Nebraska). 
2.1.1 Significance of 550 and 700 
run bands 
nm) 
The reflectance bands of the 
soybean leaf reflectance spectra were 
correlated with each other (Table 1). 
Most of the bands in the PAR region 
correlate highly with each other. It 
appears that the 550 nm and 700 nm 
bands have the highest correlation (r 2 = 
0.992). This relationship is visible in the 
absorption of the pure pigments (Fig. 1) 
in which the 550 nm and 700 nm bands 
correspond to the minimum absorption of 
the photosynthetic pigments. The 
significance of this relationship is such 
that in leaf level reflectance, a ratio of the 
550 nm and 700 nm bands is constant 
regardless of the differences in chlorophyll 
concentrations. When the 550 nm bands 
are plotted against the 700 nm reflectance 
bands of the soybean leaves with varying 
leaf pigment concentrations, this 
relationship is well illustrated (Fig. 2). It 
is observed that beyond 700 nm where 
absorption due to the pigments is 
minimal, the correlation with the 550 nm 
band drops. This is possibly due to the 
dominance of the effect of leaf structure 
on vegetative reflectance beyond 700 nm. 
The 700 nm band is located at 
the boundary of the region where 
reflectance is dominated by pigments and 
at the beginning portion of the Near 
Infra-Red (NIR) rising slope (red edge) 
which is due to the structural 
characteristics. Thus, the transition from 
the dominant effect of the pigment 
absorption to NIR vegetative 
characteristics (i.e., scattering) occurs in this region. 
(I) Wavelength (nm) 
Figure 3 
(I). Mean (n=10) reflectance spectra of nitrogen 
treated soybean leaves. (II). (a) is a chlorophyll 
absorption minima line, (b) is defined as CAR