204 International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004 
  
  
  
  
  
Wavelength (nm) 
located at the bottom of the soil mass, ended with control 
VI) 1.1 2. MATERIALS AND METHODS 50cm and zero cm. The canopy reflectance of the non-stressed 
nal Spectral measurements were the measurements of reflected alfalfa may be mainly dependent on illumination geometry and 
VI radiation from the alfalfa canopy, which was grown inside canopy structure; hence the leaf optical properties were believed 
> in | lysimeters, in the field by a high resolution to remain unchanged. 
the spectroradiometer, ASD FieldSpec. The wavebands taken 
7 | ranged from 400 — 2500 nm at a bi-weekly collection of 1 
on | reflected radiation along the growing  season.Other 9 0.8 
ine | biophysical measurements taken include leaf area index, dry 8 0.6 
: : © 0.4 
Ace | matter content, chlorophyll content, , and soil moisture 3 or fs 
ON | content 0 7" 
is | 400 700 1000 1300 1600 1900 2200 2500 
hip | The lysimeters drain freely to the atmosphere through pipes 
| 
| 
valves. Riser tubes was connected to the outlet pipes after the : 2s 
| e e Pip Figure 1. Spectral reflectance of alfalfa under 150 cm water table 
valves. The length of the risers will correspond to each water 
  
  
  
  
  
  
  
  
ote | 
89) | table depth. 
ture 
oa The experiment was conducted under field condition at the 
C | 
t6 | Agriculture and Veterinary Training and Research Station, 
3 
pas | King Faisal University, Al-Ahsa to determine water stress of 
: | alfalfa under different levels of water tables. | 
atio | | 1 
the | 0.8 
sept | A split plot design in four replicates will be used. Four water 9 06 
| table depths: 150, 100, 50, 0 cm will be occupied the whole = 
tual 2 “04 
MT: | plot. The soil textural class is a fine sandy loam. The = 
ET = 02 
and experimental plot was a concrete-made lysimeters (1.30 m | ^ modiis. 
ted diameter and 2.2 m deep). The local cultivar *Hassawi" will | 400 700 1000 1300 1600 1900 2200 2500 
SM be planted at seeding rate 60 kg/ha. The seed will be | Wavelength (nm) 
site inoculated with appropriate commercial rhizobial inoculant. | 
ion In each experimental plot a dosage rate of 450Kg P,Os/ha Figure 2. Spectral reflectance of alfalfa under 100 cm water table 
| was given in a split application after each cut. 
wed Normalized Difference Vegetation Index (NDVI) was 
sed computed as: 
ois (NIR - R)/(NIR + R) where R = Red, NIR = Near Infrared | 
D | 1 
wavebands in electromagnetic spectrum. Soil Adjusted | 
Ove | 0.8 
Vegetation Index ( SAVI ) computed as: [(NIR - R)/(NIR + 6 0c 
t . 
aps R+0.5)]1.5. Í da 
¢ 
/ater 
8 p 02 
able 3. RESULTS | 0 LZ 89 aA 
Figure 1,2,3, and 4 show spectral reflectance of alfalfa | 400 700 1000 1300 1600 1900 2200 2500 
ranged 400-2500 nm for all treatments. As can be seen from |  Wavelenah (nm) 
| aveleng 
these figures that the spectral reflectance ratio of alfalfa has 
nn : Figure 4. Spectral reflectance of alfalfa under 50 cm water table 
been affected by the level of water table. The highst ratio 
was experienced for 150cm and 100cm and the lowest for 
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