and biomass which is reflected in ND values. The plateau for 
irrigated plot is more flat as compared to unirrigated crop and 
the decline in ND for unirrigated crop is faster because for 
stressed plant early chlorosis takes place as it matures faster, 
Figure 1 and 2 represent the dynamic nature of the wheat 
crop and the effect of water stress on it. It is clear that the 
effect of water stress on the crop is apparent in all the four 
spectral variables. The mechanism for the spectral manifestation 
of water stress plant canopy basically is due to a reduction in 
the chlorophyll density and leaf area index or biomass of the 
plants. 
Regression analysis between spectral data and physiolo- 
gical parameters showed that red and IR spectral data were highly 
related to leaf area index, chlorophyll content and leaf dry bio- 
mass (Table 1). 
TABLE 1 
Linear Correlation Coefficients between the four spectral variables 
and the plant physiological parameters 
> cD wD sa SOD ed EN GHD GED THD SND MN GE Gu SN AD CI GED GD GED ID ED Gu) ED ER ED EIN ED ED ED EBD ED ED aaa uet = mn—Ó—— Po SEIN CE MS SD ED SED GER GE ER MD ED AR SD ED DD 
Plant Physio- 
logical Red IR IR/Reda ND 
parameters 
Leaf Area Index -0. 7] 0.87 0.82 0.83 
Leaf Dry Biomass -0.85 0.86 0.87 0.85 
Chlorophyll content -0,82 Q.73 0,82 0,81 
um un ae eu au» aus Uum UM qe GP Cum qua GS A Up Get GP ue ae Gem UM ND Nem GH GD Ga Se Ge SS gen Gr 008 e en o e SS ES py a—— c —  À —  À i u— c Y — e e 
The ratio IR/red reflectance was the spectral variable 
most highly and linearly correlated with these three physiological 
parameters (Figure 3, 4). Red reflectance is seen to be negatively 
correlated with leaf area index, dry biomass and chlorophyll 
content. Whereas IR reflectance, IR/red and ND showed positive 
correlation with these plant physiological parameters. Similar 
relationship between the spectral data and leaf area index and 
biomass has been reported by Holben et al 1980 for Soyabean and 
by Tucker et al 1980 for alfalfa crops. 
It is seen that out of the four spectral parameters IR/ 
red ratio is the most potential parameter for the assessment of 
plant physiological parameters. The red and infrared data, while 
useful in some regards, did not compensate for differences in the 
spectral irradiance at the times of data collection, whereas the 
ratio IR/red minimizes this variation in the spectral data and 
also it is found to be highly and linearly correlated with leaf 
area index, chlorophyll content and biomass. 
1078