poster - International Conference of Agricultural Engineering

The final enhanced images were segmented by choosing suitable thresholds to separate the
wetted area of the soil column from the background. A threshold value is selected to provide
a binary image. When the value of the pixels in an image is greater than the threshold, the
image becomes white and when the value of the pixels is smaller than the threshold, the
image becomes black. The resulting image is called the binary image. A binary image
consists only of black and white pixels representing background and the wetted area,
respectively. At zero time the wetted area equals zero since there is no wetted area in the
column. After few seconds, water starts to distribute and penetrate inside the soil column and
the column starts to be wet consequently. The same algorithm for image analysis to extract
wetted area was carried out for all images captured at different time by using routine script
developed using Matlab 7.1 and its image processing toolbox (Release 14, The MathWorks
Inc., MA, USA).
2.4. Model Validation
In order to apply the model validation, field experiment were conducted at the experimental
farm, agriculture faculty of Suez Canal University. The experiment was setup to allow testing
of 4 emitters. The system consists of main lines (3 inch.), pressure regulator, pressure gage,
water meter, valves, lateral lines (20 mm. diameter), and emitters. The design discharge
rating of emitter was verified for the installed system. The coefficient of variation of the
discharge was found to be less than 0.5 which is considered to be good. Depth of wetting
front and wetted soil volume was observed in the field by measuring radius and depth of the
soil from point source of trickle irrigation.
3. Results and Discussion
Image analysis of the soil images has only involved separation between dry and wetting area
of the soil column. A depth-dependent relationship was found between the time, discharge
and the wetting areas. Figures 3 and 4 show the change in wetting front under drip irrigation
at different times for both the sandy and sandy clay loam soils.
After 25 min 174 min 60 min 380 min
Sandy soil
Sandy clay loam soil
FIGURE 3: Change in soil wetting area under drip irrigation at different times
In case of sandy soil, the wetted area reached 50% from the whole area of the column after
only 74 min; meanwhile it takes 130 min to wet the same area of the sandy clay loam soil
column. The time taken to wet the whole column (100%) was 174 and 380 min in case of
sandy and sandy clay loam soil respectively indicating that the sandy soil has high infiltration
rate compared to the sandy clay loam soil. Moreover, as shown in Figure (4) the relationship
between wetted area and time is not linear. The best fit line for both types of soil texture is