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.