th 
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meter 
Physiological parameters such as Green Leaf Area Index, 
Dry biomass, Chlorophyll concentration, were concurrently measured 
at the same interval throughout the growing season, After every 
15 days, all the plants from one square meter area were harvested 
at ground level and Leaf area was measured by an automatic leaf 
area meter (Model Hayashi Denkoh and Co. Japan), the plants were 
oven dried to give leaf and stem dry weights of the plants, All 
weights were presented on a per square meter ground area basis. 
Leaf area was used for commuting leaf area index. Chlorophyll 
concentration was measured using the method of Arnon (1949). 
3, RESULTS AND DISCUSSIONS 
The red and IR reflectance were plotted against the 
number of days after sowing (Figure 1). Figure 1 (a) gives the 
variation of red reflectance of wheat crop throughout the growing 
season, In the beginning, the red radiance decreases very rapidly 
with time because of increased chlorophyll absorption, This 
increase in absorption is due to increase in chlorophyll concen- 
tration in the plants and also because of increased green leaf 
area index, The red radiance decreases until the growing season 
wanes and senescence begins. The red radiance for irrigated wheat 
crop shows a saturation behaviour fram 55 to 100 days. A. rapid 
increase in the red radiance occured after 100 days. due to chloro- 
sis of the maturing crop. The red reflectance for stressed (un- 
irrigated) plants was always higher than that of irrigated one. 
The infrared reflectance versus days after sowing curve 
(Ficure 1 b) showed a gradual increase with time to a maximum at 
70 days (for irrigated plot) followed by a decrease due to senes- 
cence, The peak for unirrigated plot comes earlier than the 
irrigated plot. This is becuase of the fact that the unirrigated 
crop matures earlier. In the early growing season the IR radiance 
for irrigated plot is less than that for the unirrigated one after- 
ward the trend is reversed. This is because the chlorophyll 
concentration in the stressed plant increases in the beginning and 
afterwards it reduces very fast. Figure 2 a gives the variation 
of IR/red ratio with number of days. lt again shows maxima, Here 
Separation in the level of the two maxima (irrigated and unirriga- 
ted crop) is more, Again the maximum for unirrigated crop occurs 
early, The difference in the IR/red ratio value of irrigated and 
stressed crop is more in between 60 and 100 days. That means the 
descriminability to irrigated and stressed plants is more during 
this period, In order to detect stress the remote observation may 
be taken in this period. The maximum difference in the ratio 
value for the stressed and nomal crop is as high as 40%. 
Normalized difference ND = (IR-red/IR+red) is plotted 
against the days after sowing in figure 2 b. In the beginning, 
ND increased very fast as the crop cover increases (upto 55 days). 
Once the green vegetative cover is completed, ND reaches a plateau. 
During the period of crop maturation and dry down, ND declines 
gradually. The ND plateau for unirrigated plot is at lower level 
than that for irrigated one, This is because the principal 
factors influencing ND measurements are chlorophyll density and 
the green leaf area index. The stress conditions restricts the 
plant growth by affecting chlorophyll density or leaf area index 
1015