INTRODUCTION
The main objective of irrigation is to apply to
the crop root zone the optimum amount of water that the crop needs for
development and also that cannot be provided by rains.
The sprinkler irrigation method, one of the pressurized
irrigation systems, takes water from a source and sprays it to the atmosphere
as droplets by means of an enclosed system and under pressure. The water
is transmitted to the surface of the soil in equal distribution with the
sprinkler irrigation system to obtain uniform distribution in the crop
root zone (Keller and Bliesner, 1990).
Sprinkler irrigation systems, as opposed to furrow irrigation,
transmit water to the field independently of topography. Spacing and discharge
of sprinkler determine the application rate which should be less than
infiltration rate for not producing surface runoff.
The degree of uniformity of water distribution depends
on the water distribution styles and features of sprinkler nozzles. The
basic function of sprinkler nozzles is to distribute water uniformly,
without causing surface flow and excessive drainage from the root zone.
For this reason, the sprinkler nozzle is considered to be the most important
element of the system. The performance of the sprinkler nozzle determines
the productivity and efficiency of the whole system (Keller and Bliesner,
1990; Wilson and Zoldoske, 1997). A successful irrigation regime can be
determined by researching all the relevant factors and then effectively
using the data produced.
In sprinkler irrigation, water distribution figures for
nozzles at different spatial arrangements are determined by considering
the soaking field observed for each value of pressure and the size of
nozzle. It is necessary that the determined water distribution be at an
acceptable level. This is determined by the equal distribution coefficient
(Keller and Bliesner, 1990; Allen, 1993). Uniformity coefficient developed
by Christiansen in 1942 is stated below (Vories and Von Bernuth, 1986;
Losada et al., 1990; Allen, 1993)
| CU |
= |
Equal distribution coefficient developed by Christiansen
(%) |
| Z |
= |
The amount of water measured in each container while testing uniformity
(mm, mL) |
| x |
= |
|z-m|=The total absolute value of deviations from average of the
amount of water measured in all accumulation containers (mm, mL) |
| m |
= |
(Σz)/n=Average amount of water (mm, mL) |
| n |
= |
The number of water accumulation containers |
A CU coefficient of 84% is desirable. Arrangement styles
that have the results less than this value should not be used (Keller
and Bliesner, 1990).
In practice, it`s not possible to obtain 100% of uniformity
on the irrigated area because nozzles distribute water on a circular area,
with overlaps between areas of water distribution. It`s impossible to
have equal water distribution on the areas that are being irrigated (Zoldoske
et al., 1994; Stryker, 1998).
The main factors affecting water application (water distribution
uniformity) are sprinkler nozzle type, operating pressure, nozzle diameters,
nozzle elevation, wind speed, heat and damp (Keller and Bliesner, 1990;
Allen, 1996; Wilson and Zoldoske, 1997; Tarjuelo et al., 1999;
Loule and Selker, 2000).
The uniformity in water distribution depends on the distance
between the sprinkler nozzles as well (Wilcox and Swailes, 1947). As sprinklers
are spaced further apart, uniformities usually decrease (Tarjuelo
et al., 1999; Joshi et al., 1995).
No sprinkler nozzle should be operated without providing
the desired over-lateral and inter-lateral overlap. Desired degree of
overlap is achieved by the sprinkler pattern of nozzles and wind conditions.
Spacing should be closer in windy weather. Lateral and nozzle spacing
should be determined according to different speeds and directions of wind
and different nozzle pressures (Chawla and Narda, 1995; Faci and Bercero,
1989; Abo-Ghobar and Al-Amoud, 1993). Since windy conditions negatively
affect the distribution of water, the spaces between nozzles should be
decreased. It is generally suggested that irrigation be carried out when
wind speed is lower than 2.5 m sec-1 (Ruzicka, 1992). If wind
speed increases, the uniformity coefficient decreases (Vories et al.,
1987; Padmanabhan, 1997; Tarjuelo et al., 1999).
Another factor affecting efficiency is sprinkler height
which has a great effect on sprinkler uniformity, especially in windy
weathers (Abo-Ghobar, 1992). Sprinkler should be at the same height and
able to move freely for dispersal of the water droplets. Sprinkler nozzles
should also be vertical to the surface of land.
In this research, the single nozzle trial method has
been used because, it enables the experiment easily to determine the uniformity
coefficient for the different spacing, mostly used in application and
it gives sufficient and satisfactory results for the water distribution
figures.
The aim of this research was to assess water distribution
by using the single nozzle trial method and determine the uniformity distribution
coefficient for different arrangement spaces. The objective is to estimate
and quantify the effect of main factors influencing the water distribution
at the field level in the single nozzle set systems. In addition, a set
of recommendation will be given for design and management of these systems
for the Middle Black Sea region and for other regions where environmental
and agricultural conditions could be similar.
MATERIALS AND METHODS
Material:
The experimental field was located on the campus of Ondokuz Mayis University
in Samsun, Turkey at 2003. Almost 0.3 ha of experiment field was leveled
to 0.0% incline. This incline is important for the water catcher containers.
The water supply was provided from a well that was 150
m distant. The flow rate of the well was 5 L sec-1. A valve
that can regulate the pressure and a manometer just under the sprinkler
nozzle were used. The flow rate of the sprinkler nozzles was determined
with a chronometer and a container, of known volume.
Five different sprinkler nozzles which are widely used
in Middle Black Sea region were used. The nozzles used were Bereket 3
and Bereket 2, little plastic sprinkler nozzle produced by Egeyildiz,
15/15 L plastic sprinkler nozzle by Goktepe and the sprinkler nozzle by
Atesler.
The height of the nozzle was measured 76 cm from the
surface. In order to determine the speed of nozzle rotation, a chronometer
was used. For the speed and direction of wind which are important for
the distribution figures, an anemometer and a compass were used.
In test, to collect water from the sprinkler nozzles,
576 catch cans (plastic containers) with a 15 cm height and 11.2 cm diameter
were used.
The sprinkler head was fixed in the middle of a square
field 50x50 m. An approximate 2 m square grid of catch can was located
within the space given above. The evaluations were carried out in bare
soil.
The sprinklers were operated under different operation
pressure in atmosphere (atm). Operation pressures were constant throughout
procedure. The sprinkler heads operated pressure were suggested in the
brochures of the firms; the Bereket 3 sprinkler nozzle was operated at
1.5, 2.0, 2.5, 3.0, 3.5, 4.0 and 4.5 atm. Bereket 2 at 2.0, 2.5, 3.0,
3.5 and 4.0 atm Egeyildiz at 2.0, 2.5 and 3.0 atm Goktepe at 2.0, 2.5
and 3.0 atm and Atesler at 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 4.8 atm. Each
test operated 3 h.
Water throwing distances, flow rates and rotation speeds
were obtained. Collected data taken from field experiments. Each experimental
data entered a computer program called CATCH3D. CU coefficients and 3D
water distribution graphs were determined by using the values obtained.
Method:
During the trial, the operation pressure and the
flow rate was controlled. The rotation speed of the nozzle as cycles/minute
was measured. The speed and direction of the wind was measured every 15
min at a height of 2 m with an anemometer. At the end of the trial, the
amount of water accumulated in each catch can was measured with cylinders
(mL). These experiment procedures were repeated for each sprinkler nozzle
at their respective pressure intervals.
Data obtained was entered into the Catch3D computer program
developed by Allen (1996). First, the water distribution figure of in
the single nozzle was determined and the results have been assessed by
determining the Christiansen Uniformity Coefficients on nozzle spacing.
The CU coefficient can be determined with CATCH3D by
using input the duration of the experiment, the direction and speed of
the wind, the flow rate and water volume in the catch can. The water distribution
graphs had drawn by program in three dimensionally (3D). The program can
be uses only for field data. It does not produce new data. The most important
feature of the program is that it can determine the spacing and CU coefficient.
This program is used because it provides rapid and correct calculations
and it produces graphics and results directly and rapidly by disregarding
complexity and the calculations errors in traditional methods (Allen,
1996).
The figure for water distribution for spacing is generally
obtained by applying the overlap method while being used the nozzle in
sprinkler systems. This is a time-consuming but cheapest method. In addition,
water distribution graphs at different lateral and nozzle spacing can
be obtained and plotted without entering the data again. In order to determine
whether distribution in the figures is acceptable or not, the CU values
are integrated with all these graphics. Thus, it is possible to find suitable
spacing by trying more alternative lateral and nozzle spacing in a short
time. It also prevents the complexity and manual calculation errors of
traditional methods.
RESULTS AND DISCUSSION
During the field experiments data were entered program as given
above. The results for the Bereket 3 are given in the Table 1. The 3D
water distribution graph for the Bereket 3 at 1.5 atm, is given in Fig.
1 and the water distribution graphs for different spacings and CU
coefficients in Fig. 2.
For the Bereket 3 sprinkler nozzle at 1.5 atm pressure,
the wind speed was 1.0 m sec-1. At this pressure, a flow rate
was 0.30 L sec-1 and a wind speed of 1.0 m sec-1
there was no accumulation of water distribution in the direction the wind.
Water distribution graphics and CU coefficients for different spacing
for Bereket 3 were examined, Keller and Bliesner (1990), Allen (1993)
and Tarjuelo et al. (1999) have reported that CU coefficient should
be more than 84%. If this is taken into consideration, the spacing that
give a value of CU>84% for Bereket 3 are 6x6 and 6x12 m. It is therefore
not appropriate to have the sprinkle nozzle operating at other spacings.
Christiansen Uniformity coefficients of the nozzles at different spacing
and pressure are described in Table 1. The spacings giving
the value of CU>84.4 for the Bereket 3 are 6x6 and 6x12 m at 1.5 atm;
6x6 and 6x12 m at 2.0 atm; 6x6, 6x12 and 6x18 m at 2.5 atm; 6x6, 6x12,
6x18, 12x12 and 12x18 m at 3.0 atm. At 3.5 and 4.0 atm, the CU
| Table 1: |
Christiansen Uniformity
Coefficients of Bereket 3 sprinkler nozzle in the square and rectangle
arrangement styles (nozzle diameter, 5 mm) |
 |
 |
| Fig 1: |
Three dimensional
water distribution, the data observed from Bereket 3 sprinkler nozzle,
drawn with the Catch3D. (The flow rate, 0.30 L sec-1,
working pressure, 1.5 atm, the wind speed, 1.0 m sec-1) |
 |
| Fig 2: |
The three dimensional
appearance of water distribution for different spacing in 1.5 atm
pressure of Bereket 3 sprinkler nozzle and its uniformity coefficient |
coefficient is below 84.4% for all configurations. The suitable arrangements
for 4.5 atm, which was the highest pressure of the Bereket 3 sprinkler
nozzle, were 6x6, 6x12 and 6x18 m. The results with other sprinkler nozzles
are given in Table 2-5.
Technical features of sprinkler nozzles and the suitable arrangements
are shown in Table 6. The main objective in sprinkler
irrigation is to choose the sprinkler nozzle that enables wide spacing,
low pressure and appropriate water distribution. More than one solution
that is suitable for the conditions can be found. For this reason, an
irrigation project is planned using the appropriate sprinkler nozzle and
the water emitting speed nozzle into consideration.
Table 6 shows that the CU coefficient of the sprinkler
nozzles tried is rarely over 84.4% at a working pressure. Considering
the necessity of choosing the wide spacing for economic reasons, the most
suitable spacing
| Table 2: |
Christiansen Uniformity
Coefficients of Bereket 2 sprinkler nozzle in the square and rectangle
arrangement styles (nozzle diameter, 10 mm) |
|
|
| Table 3: |
Christiansen Uniformity
Coefficients of Egeyildiz sprinkler nozzle in the square and rectangle
arrangement styles (nozzle diameter, 4.5x5.0 mm) |
|
|
of the Bereket 3 sprinkler nozzle at different working
pressures were determined as 6x12 m at 1.5 atm, 6x12 m at 2 atm, 6x18
m at 2.5 atm, 12x18 m at 3.0 atm and 6x18 m in 4.5 atm. No arrangement
is suitable for 3.5 and 4.0 atm.
For the Bereket 2 Sprinkler nozzle, which is similar
to the Bereket 3, the most suitable spacing was determined as 12x12 m
at 2.0 atm, 6x12 m at 2.5 atm, 6x12 m at 3.0 atm, 12x18 m in 3.5 atm and
6x18 m at 4.0 atm.
Table 4: |
Christiansen Uniformity
Coefficients of Goktepe sprinkler nozzle in the square and rectangle
arrangement styles (nozzle diameter, 5.5x4.5 mm) |
 |
| Table 5: |
Christiansen Uniformity
Coefficients of Bereket 3 sprinkler nozzle in the square and rectangle
arrangement styles (nozzle diameter, 8 mm) |
 |
For the Egeyildiz, the most suitable spacing was determined as 6x6 m at
2.0 atm, 6x18 m at 2.5 atm and 6x12 m at 3.0 atm.
For the Göktepe nozzle, the most suitable spacing
was 6x18 m at 2.0 atm, 6x12 m at 2.5 atm and 6x6 m at 3.0 atm.
For the Atesler nozzle, the most suitable spacing was
6x6 m in 2.0 atm, 6x6 m at 2.5 atm, 6x18 m at 3.0 atm, 6x6 m at 3.5 atm,
12x18 m at 4.0 atm, 6x18 m at 4.5 atm and 6x18 m at 4.8 atm.
According to the results, the most suitable pressure of the Bereket 3
nozzle is 3.0 atm and the spacing is 12x18 m. Similarly, the most suitable
operating parameters for the other sprinkler nozzles are 3.5 atm and 12x18
m spacing for the Bereket 2; for Egeyildiz, 2.5 atm and 6x18 m spacing;
for Göktepe, 2.0 atm and 6x18 m spacing; and for Atesler, 4.0 atm
and 12x18 m spacing. The sprinkler nozzle that can be used most appropriately
and economically with wide spacing and under low pressure is the Bereket
3 nozzle. These results were obtained when there was low wind speed (0-2.5
m sec-1). For this reason, if the wind speed exceeds the suggested
limit, wider spacing than that suggested should be avoided.
The aim of this research was to determine the technical
features of the nozzles under the field conditions. Speed and direction
of wind in irrigation by the sprinkler method have significant effects
on water
| Table 6: |
Technical features of the sprinkler,
which can be used in application, sprinklers that were tried and applicable
spacing |
 |
distribution uniformity and the performance of the system.
For this reason, irrigation applications should be made when the wind
speed is low and laterals should be fixed parallel to the dominant wind
direction.
CONCLUSIONS
The experiments data and model simulation output
tables and figures have permitted to identify the conditions best suited
for each sprinkler. As a consequence, technical criteria can be used for
the selection of the adequate sprinkler and nozzle diameter for the prevailing
operation and environmental conditions at the given location. CU tables
and figures can also be used in given sprinkler layout to optimize irrigation
management in response to the operating pressure and wind speed. These
results could be implemented by advanced irrigation programmers.
In the context of growing concerns about water availability,
it is very important that this is made available to farmers and irrigation
specialists.
ACKNOWLEDGMENT
The authors thank Gregory T. Sullivan of Ondokuz
Mayis University for his comments.
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