004 
inin 
Soil 
the 
of 
tion 
).) 
inge 
Map 
oint 
rban 
and 
Soil 
y of 
  
SPECTRAL REFLECTANCE OF ALFALFA GROWN UNDER DIFFERENT 
WATER TABLE DEPTHS 
Y.Y. Aldakheel', A.H. Assaedi, and M.A. Al-Abdussalam 
Water Studies Center, King Faisal University, POBox 420, Hofuf, 31982 
Saudi Arabia, e-mail: yaldakheel@kfu.edu.sa 
Commission VII, WG VII/2 
KEY WORDS: Multispectral, Detection, Agriculture, Monitoring, Reflectance 
ABSTRACT 
The main objective of this study is to determine the growth response and water use effeciency of alfalfa (Medicago sativa L.) grown 
in the field under four water table levels and two rates of water supply under the climatic condition of Al-Hassa oasis in Saudi 
Arabia. The potential use and management of water table depth, to function as sub-irrigation system without increasing the 
accumulation of salts in the root zone is a valuable agricultural resource in arid regions. Therefore, the water table should be 
maintained at optimum depth to save both water and energy. 
Plant water stress can limit productivity and has an effect on plant physiology and canopy architecture. Changes in water status of a 
canopy can have indirect effects on remotely sensed optical reflectance and thermal emittance, which can be measured in the field 
and related to crop conditions. 
Biophysical and spectral measurements were taken in the field of alfalfa grown inside concrete lysimeters .Thses include biophysical 
variables, such as:leaf area index, dry matter content, soil moisture content, and monitoring of water table depth. 
Moreover, measurements of reflected radiation from the alfalfa canopy in the field by a high resolution spectroradiometer were 
taken at full cover during the growing season. 
Results from this study showed that alfalfa grown at water table depth between 100-150 cm was better than that grown at shallow 
(50 cm) or very deep water table (deeper than 150 cm). Spectral response of alfalfa was positive and showed that remotely sensed 
data could be used to detect water stress of alfalfa grown under the climatic and environmental condition of Al-Hassa. 
This study may provide information and knwledge that can lead to better management of rrigation water and help farmers to 
conserve water by applying only the right amount of irrigation water. In addition, transferability of results among other agricultual 
crops in different areas. Moreover, detection of crop water stress in early stage by application of remote sensing technique. This 
study also might help in design of proper drainge depth suitable for forage crops with respect to soil and climatic conditiond. 
1. INTRODUCTION and large scale agricultural projects, so is very important the 
Alfalfa (Medicago sativa L.) has a very hi gh yield potential crop is monitored regularly to study the influencing factors of 
compared with that of other forage crops. It also is an integral its growth and productivity by remote sensing technology. 
component of many crop rotations because of its ability to fix 
nitrogen, improve soil structure and tilth, and control weeds Alfalfa is very responsive to water stress. The reduction in 
in subsequent crops. In Saudi Arabia, alfalfa is considered of yield could reach up to 41%, when ET was reduced to 56% 
of the maximum (Asseed et al., 1981) The consumptive use 
of alfalfa was determined by Asseed et al. (1981) as 28800 
highly economic value, it accounts for about 30% of crop 
production. It was studied extensively in the past regarding 
culture, growth, tolerance, yield, irrigation, etc. However, the m/ha/year for non-stress condition under Al-Hassa climate. 
research in drainage requirements of alfalfa in the region is 
very limited. Recently, alfalfa is now cultivated in large areas 
  
Le orresponding author 
1143