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 LICOR1800
LICOR1800 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
