PERFORMANCE OF GRAPEVINES UNDER IRRIGATION SYSTEMS - Management, Performance, and Applications of Micro Irrigation Systems - page 252

and 5) not feasible in soils with faster infi ltration rate. And also, bubbler irrigation is
very sensitive to changes in pressure head and a constant head-source is essential
for a commercial orchard or plantation. A change in pressure head at the inlet results
in nonuniformity of application at each outlet. He found also that pressure head of
one meter is very small and small changes in head can thus have a marked effect on
the fl ow rate, which is fi xed once the system is installed and is not easily changed.
Larry [53] showed that in bubbler-irrigation system water is applied to the land
surface as a small stream. Habib and El-Awady [33] stated that the discharge uni-
formity of bubbler irrigation system can be controlled by varying the tube diameter
and/or length and/or using a valve for each bubbler in a long lateral line. Yitayew
et al. [86] showed that the name of that low-head bubbler system is derived from
the fountain of water streaming out from the hoses, and from the bubbling noise
made as air escapes from the pipeline when the system is turned on. Yitayew and
Reynolds [87] compared the low head gravity fl ow bubbler irrigation system that is
commonly used for tree crops. The bubbler system has a defi nite advantage in
cost savings in addition to reduced water usage and equal or better water distribu-
tion uniformity.
20.1.1.3 MODIFIEDSURFACEIRRIGATION WITH GATED PIPES
Layei et al. [54] studied the effect of irrigation methods and levels on yield and
quality of hybrid tomato seeds and found that seed yield obtained from furrow irriga-
tion was significantly lower than those of bucket watering and drip irrigation. Fur-
row irrigation also resulted in higher proportion of fruits that shown a symptom of
blossom and rot. In clay soil, bucket watering and drip irrigation gave a significantly
higher fruit weight and seed yield than furrow.
Charles [20] reported that furrow spacing was easy to adjust when furrows
are used to irrigate permanent crops such as trees or vines, and the number of fur-
rows/row can be varied. The same effect can be achieved by irrigation every other
furrow on row crops when it is desired to apply a small depth of water during
one irrigation.
El-Sayed [27] studied the different orifi ce discharge rates ranging from 0.1 L/
sec (ls -1 ) to 0.6 ls -1 . From the view point of the allowed discharge in irrigation fur-
row, he found that a discharge of 2 ls -1 is recommended for each-one meter of fur-
row width. And the proposed system can be used to irrigate long line and long strips
with lengths between 100 to 180 m, ii) pressure head needed to operate the system
(ranged between 15 cm to 100 cm), and the required head to operate the system
in the fi eld was 50 cm or less, therefore pumping unit is not a must. His results
indicated that there is an agreement between the theoretical predicted hydraulic pa-
rameters and the actual ones.
20.1.2 EFFECTSOFIRRIGATION SYSTEMS ON GRAPE YIELD AND WATER
USE EFFICIENCY
Grape is the second major fruit crop in Egypt. However, the grape area in the Wadi
and valley Delta occupied about 50% of total area in 2004 (about 155,743 feddans).