351
spectral
[1 ]
VI and
Goeff. of
Deter., r^
.930
.887
side]
20
30
10
.867
.857
.969
.942
.581
.469
.835
.825
.878
.751
.986
.969
rent in the
riable (y)
esented for
4
2
10 20 30 40
PVIZ1
Figure 1. Hie first term
of equation [ 1' ], FVI
versus LAI, for each of
the crops cotton, wheat,
and corn (maize) and the
exponential and power
expression (Table 2) fits
for each.
0 2 4 6
LA1/C0SZ2
Figure 2. Hie second term
of equation [1'], LAI
versus APAR, for three
crops and the exponential
and power expression
(Table 2) fits for each.
PVI*C0SZ 1 /C0SZ2
Figure 3. Right hand side
of equation [1'], PVI
versus APAR, for three
crops and the linear and
power expression (Table 2)
fits for each.
each term in equations [1'] for snail plot
experiments using cotton, wheat, and maize. PAR
light absorption could be estimated almost as well
for cotton and corn from the perpendicular
vegetation index, PVI, (right side equation [1 ])
as from the leaf area index (2nd term on the left).
(Results for all relationships were somewhat poorer
for wheat (Table 2)). Hiis finding implies that the
vegetation indices are a good measure of the
photosynthetically active tissue in the canopy.
Hi us APAR can be estimated directly from VI.
Alternatively, LAI expressed in terms of VI can be
inserted into APAR versus LAI expressions in the
literature to estimate APAR. Hie ability to
estimate APAR remotely is important because of the
close association between cumulative APAR and above
ground dry matter of crops.
VI and APAR became asymptotic to the LAI axis at
large LAI (Figures 1 and 2), respectively, whereas
APAR was nearly a linear function of VI for each
crop (Figure 3). In general, these interrelation
ships demonstrate the unity among LAI, light
absorption, and yield that is consistent wnth
growing condition and stress influences on canopy
size and field observed yields. Therefore, direct
spectral observations expressed as vegetation
indices can provide valuable current information on
crop prospects. In addition the "pure spectral"
observations of SCA can provide useful independent
estimates of LAI and APAR for use in conjunction
with the "pure nonspectral" plant process models of
crop development and yield.
REFERENCES
Anderson, M.C. 1971. Radiation and crop structure,
pp. 412-466, in Plant Photosynthetic Production
(Z. Sestak, J. Catsky, and P.J. Jarvis, eds.)
Junk. The Hague.
Asrar, G., M. Fuchs, E.T. Kanamasu & J.L. Hatfield.
1984. Estimating absorbed photosynthetic radiation
and leaf area index from spectral reflectance in
wheat. Agron. J. 76:300-306.
Black, A.L. & J.K. Aase 1982. Yield component
comparisons between US and USSR winter wheat
cultivars. Agron. J. 74:436-441.
Colwell, J.E. 1974. Grass canopy bidirectional
spectral reflectance, Proc. 9th Int'l. Syrnpos.
Remote Sens. Environ. Vol. II, pp. 1061-1086.
Univ. Michigan, Ann Arbor, USA.
Charles-Edwards, D.A. 1982. Physiological
determinants of crop growth. 161p. Academic
Press, New York, NY.
