Tucker et al (1979) monitoried corn and soybean growth 
and development by red and photographic infrared data collected 
throughout the growing season, They found significant correlation 
between the radiance data and the bianass, plant height, percen- 
tage crop cover, percentage crop chlorosis and percentage leaf 
loss. Holben et al (1980) correlated the spectral data with leaf 
area and biomass. Tucker et al (1981) quantitatively correlated 
the radiance data with dry matter accumulation in winter wheat. 
The present paper describes the results of an experiment 
in which red and infrared spectral data were collected from wheat 
crop under irrigated and unirrigated conditions throughout the 
growing season, The spectral data were correlated with the plant 
physiological parameters viz. leaf area index, chlorophyll content 
and dry biomass. Significant correlation was found to exist 
between the spectral and the plant physiological parameters. 
2. MATERIALS AND METHODS 
The experiment was conducted during December 1980 to 
April 1981 on wheat crop in a field of sandy loam at the Indian 
Agricultural Research Institute (IARI), New Delhi, Five experi- 
mental plots of size 4.5 m x 7.5 m each, of which three plots were 
irrigated while the remaining two had only presowing irrigation, 
Before sowing the plots were irrigated ploughed and fertilized 
(75 Kg N, 60 Kg P and 60 Kg K per hectare). The variety of wheat 
selected for this study was 'Sonalika'. 
The radiance data for all the five plots were measured in 
in red (665-685 mm) ana infrared (815-835 mm) region. The radian- 
ce was measured by a modified version of UDT power meter/Radiometer 
at an interval of 15 days throughout the growing season of the 
crop, The radiometer was mounted in the field on a flexible 
tripod stand having maximum and minimum height of 10 and 5 feet. 
To reduce the error caused by positioning the radiometer, ten 
spectral measurements were made over each plot and the mean for 
each band was calculated. All further calculations were performed 
with these mean radiance values. All spectral data were collected 
in between 1100 and 1500 hours Indian Standard Time (IST), measured 
normal to the ground surface at a height of 6 feet above the plant 
canopy, and were collected in direct sunlight with cloud less or 
partially cloudy, skies. 
Immediately after each spectral measurement on a given 
plot, a solar intensity calibration reading was taken from a BaSo, 
panel. The irradiance obtained by using BaSo, panel was used to 
calculate the reflectance of the crop. 
The red and infrared spectral reflectance data were used 
to form the IR/red reflectance ratio and the normalized difference 
(ND) where 
ND = (IR-red)/(R+red) 
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