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Water and Environment Journal. Prin t ISSN 1747-6585
Water and Environment Journal 0 (2018) 1–11 © 2018 CIWEM. 1
Introduction
Lack of water is a huge problem for many countries around
the world and for some it is a critical challenge (Rouphael
et al., 2008). In comparison with other countries in the
Middle East, Jordan has faced considerable difficulties
with respect to scarcity of water since the 1970s (THKJ,
2004). Jordan is classified as a semi-arid to arid region
typified by hot, dry summer and cool, low average annual
rainfall in winter (Malkawi and Mohammad, 2003).
Approximately 5% of the available water resources in
Jordan is consumed by the industrial sector and a further
22% is used by the domestic sector, with the vast major-
ity of the supply (73%) being utilized to meet agricultural
needs (Hadadin et al., 2010). To reduce the demand on
water resources, different types of water such as treated
wastewater (TWW), grey water, and industrial water are
being used to irrigate agricultural crops (Batarseh et al.,
2011). The use of TWW conserves the supply of fresh
water (FW) for drinking purposes rather than for irrigation
(Malkawi and Mohammad, 2003; Christou et al., 2 014 ).
In Jordan, the total dissolved solids in the wastewater
treatment plants varied from 700 to 1200 mg/L (Bataineh
et al., 2002). The efficiency of removing these solids
through different techniques (filters and activated sludge)
is high (Abdulla et al., 2016). Moreover, TWW has a high
nutritive value that might improve plant growth and
increase the productivity of poor fertility soils (Christou
et al., 2014). Many researchers (Almuktar and Scholz,
2015; Orlofsky et al., 2016) have recommended the use
of TWW for the irrigation of agricultural crops such as
corn, vegetables that are eaten cooked, and cut flowers.
In the main, to satisfy crop water requirements, TWW is
applied to soil by means of an irrigation system to satisfy
crop water requirements.
Microirrigation systems have many advantages over
the other types of irrigation systems such as better con-
servation of water, easier weed control, lower energy
requirements, and higher crop yield (Patel and Rajput,
2007). There are two types of microirrigation systems:
surface drip irrigation (SD) and subsurface drip irrigation
(SDI). In SDI, the lateral lines are installed below the soil
surface and, consequently, the water is applied directly
into the root zone at a discharge rate usually less than
8 L/h (Camp and Lamm, 2003). The SDI method is superior
to the SD because the former can increase the yield of
more than 30 types of crops including corn and alfalfa.
And, it can also give cotton a longer life, make more
efficient use of water, reduce water loss due to evapora-
tion, and emit a larger wetted volume in the root zone,
as well as provide the user with a much easier system
to utilize in terms of mechanical operation (Camp and
Lamm, 2003).
However, drip irrigation systems do have some draw-
backs. For instance, salts can accumulate on the top surface
of the soil, mud can be sucked into the emitters, and
Impact of irrigation water quality and envelope materials
around drip line on emitter performance in subsurface drip
irrigation
Naji K. Al-Mefleh & O’badah F. Al-Raja
Department of Natural Resources, Jordan University of Science and Technology, Irbid, Jordan.
Keywords
clogging emitters; corn yield; envelop material;
subsurface drip irrigation; water quality.
Correspondence
Naji K. Al-Mefleh, Department of Natural
Resources, Jordan University of Science and
Technology, P.O. Box 3030, Irbid, Jordan.
Email: nmefleh@just.edu.jo
doi: 10.1111/wej.12437
Abstract
A field experiment was conducted to study the effect of water quality types of
fresh water (FW) and treated wastewater (TWW) and envelope materials of coarse
sand (CS), fine sand (FS), and control (CO) on emitter performance, dry matter
yield (DMY), and water use efficiency (WUE) under subsurface drip irrigation.The
main interaction effect of water quality type and envelope material on coefficient
of variation, Christiansen uniformity coefficient, and emission uniformity was not
significant (P < 0.05), but they have a significant effect on the average emitter
discharge (Qavg), DMY, and WUE. The means of Qavg for FW with CS, FS, and CO
were 7.13, 6.94, 2.65 L/h, and for TWW, they were 6.78, 6.84, and 2.35 L/h,
respectively. The DMY under FW with CS, FS, and CO was 3083.87, 1367.95, and
417.45 kg/ha, and under the TWW, it was 2409.5, 1347.4, and 417 kg/ha,
respectively.
Naji K. Al-Mefleh and O’badah F. Al-RajaImpac t of irrigation water quality and envelop e materials
Water and Environment Journal 0 (2018) 1–11 © 2018 CIWEM.2
there can also be a greater amount of root intrusion into
the emitters. Clogging of the emitters is one of the most
serious problems associated with the use of microirrigation
systems as it results in lower system performance and
water stress in nonirrigated plants (Coelho and Resende,
2001). Moreover, the performance of the SDI is affected
by root intrusion and the entry of mud into the emitters
more than that of the SD (Lamm et al., 2002). A range of
water quality parameters can be analysed to determine
the potential for emitter clogging. Some studies (Capra
and Scicolone, 2004; Liu and Huang, 2009; Li et al., 2009;
Al-Mefleh et al., 2015) have investigated the following water
quality parameters: pH, total iron, hydrogen sulfide, sus-
pended solids, dissolved solids, manganese, calcium, mag-
nesium, and the number of bacteria. The potential for
clogging varies depending on the emitter’s dimension, the
position of the lateral lines, and flow type, which can be
either laminar or turbulent (de Kreij et al., 2003). It has
also been reported that emitter performance depends on
the emitter type, the duration of system operation, and
the quality of water used for irrigation (Liu and Huang,
2009). A recent study found that while the water type
(FW or TWW) had no significant effect on emitter discharge,
operational time and emitter type had a significant effect
on emitter discharge (Al-Mefleh et al., 2015).
The reasons for emitter clogging can be classified
into physical, biological, and chemical (Yavuz et al.,
2010). Physical clogging may be caused by factors such
as organic materials (plant residues) and suspended
inorganic materials (sand, silt, and clay). Biological clog-
ging is due to the accumulation of hydrogen sulfide
and organic sediments in the emitter and lateral lines
(Dehghanisanij et al., 2005). Acids can be injected into
the irrigation system to avoid the precipitation of cal-
cium carbonate and to reduce the pH value, while a
chlorination treatment can also be applied to prevent
and treat emitter clogging caused by algae and bacteria
(Dehghanisanij et al., 2005). In addition, it has been
found that 5–8 mg/L of Cl2 and 3–4 mg/L of ClO2 are
sufficient to control the activation of bacteria in efflu-
ent. Also, clogging by soil particles can be avoided or
at least mitigated by the use of appropriate filtration
and flushing methods. However, even though a suitable
filtration system will keep most soil par ticles out of the
system, some particles will still pass through the mesh
and settle down inside the drip lines. Hence, before
passing water through a drip irrigation system, the water
characteristics should also be analysed to tr y to avoid
emitter clogging in the first place (Capra and Scicolone,
1998). Nevertheless, in spite of such precautions, roots
and clay particles can still clog drip emitters in systems
that are buried below the soil surface (Wang et al.,
2005).
Some field studies (Ebrahimi et al., 2012; Al-Mefleh et
al., 2015) have been conducted to determine the impact
of water quality on SDI emitter performance. Others
(Al-Mefleh and Abu-Zreig, 2013; Qiaosheng et al., 2007)
have examined the wetting pattern produced by SD and
SDI. Stuyt et al. (2005) stated that the envelop materials
(coarse sand, fine gravel and crushed stone) can be used
to protect the drain pipes from sedimentation, improve
its hydraulic performance, and improve the permeability
around the pipe. And, they act as permeable constraints
to impede the entry of damaging quantities of soil par-
ticles and soil aggregates into the emitters. However, none
of the above studies investigated the effect of the water
quality and the envelope material around the line on the
clogging of the SDI systems. Therefore, the present study
examined the impact of water quality on the performance
of SDI emitters as well as the impact of two different
types of sand – fine sand (FS) and coarse sand (CS) as
an envelope material around the lateral line on crop yield
and water use efficiency (WUE) when using SDI.
Materials and methods
Experimental site
The study was conducted near to the Jordan University
of Science and Technology (32°22′′ N, 35°49 ′′ E) at an eleva-
tion of 520 m above sea level. The region in which the
experiment was conducted is considered to be an arid
region, hot in summer and cool in winter with an average
annual precipitation of 200–300 mm. Two trials for the
collection of data were carried out in the field. The first
trial took place from October 2015 to February 2016, but
was not included in this study because many of the plants
died due to frost and the amount of irrigation was low
because the evapotranspiration (ETο) was low in winter.
The second trial was carried out successfully during the
summer of 2016 (June to September) and the results of
that trial are discussed here. The soil properties of the
experimental area are presented in Table 1.
Irrigation system
In this study, a SDI system was used to irrigate corn
plants. The system consisted of three tanks (each with
a capacity of 2 m3), a pump (Taizhou Lingxin, ABAR com-
pany, Italy, 1 hp, 35-m head, and 2.4 m3/h discharge con-
nected to a storage tank of TWW), a flow meter, valves,
a filter, pressure gauge, fittings, and lateral lines fitted
with GR emitters (Fig. 1). The flow meter was used to
calculate the amount of irrigation water applied. The pres-
sure was set to 0.8 bar at the beginning of the lateral
lines and to not less than 0.7 bar at the end of the lateral
lines. The lateral lines were 20 mm in diameter and made
Impac t of irrigation water quality and envelop e materialsNaji K. Al-Mefleh and O’badah F. Al-Raja
Water and Environment Journal 0 (2018) 1–11 © 2018 CIWEM. 3
of plastic piping (polyethylene) with in-line GR emitters
installed at a spacing of 40 cm between emitters. The
discharge of each emitter was 8 L/h. The lateral lines
were covered with 5 cm of either CS or FS and buried
15 cm below the soil surface. Signs on sticks were inserted
into the soil surface at the beginning and end of the
lines to identify the locations of these subsurface lines.
Prior to data collection, the experimental area was
cultivated and prepared to install the above-described
SDI system. The lateral lines were marked and logged
out to a depth of 15 cm below the soil surface, and then
the spoiled soil was repacked over the lateral lines and
compacted until the original soil bulk density was reached.
The experimental area was divided into three blocks, and
each block was divided into six plots, with each plot
representing one lateral line. Thus, there were 18 lateral
lines in total. Each lateral line was 13 m long and had
32 emitters. The main treatments in the experiment con-
sisted of two water quality types: FW and TWW. The
sub-treatments consisted of two envelope materials – CS
consisting of par ticles of 8–9 mm in diameter; FS consist-
ing of particles 0.5–1 mm in diameter – and a control
(without CS and FS). The treatment combinations were
assigned randomly to the plots as FW with CS, FW with
FS, TWW with CS, TWW with FS, FW with control (no
envelope material), and TWW with control (no envelope
material). The various combinations of water quality type
and envelope material treatment are illustrated in Fig. 1.
Table 1 Soil properties of the field experiment
Sample Clay % Sand % Silt % Soil type
Bulk density
(gm/cm3) pH EC (μs/cm) Field capacity % Wilting point %
0–25 cm 34 44 22 Clay loam 1.31 8.3 341 0.30 0.24
Fig. 1. Schematic diagram of the three replicates of the field experiment under TWW.
Three Tanks
FM
Pump
Gauge Pressure
ValveValve
Flow
Meter
Lateral Lines
Emmiters
2m
2m
3m
2m
2m
3m
2m
2m
13 m
TWW + CS
TWW + FS
TWW + Control
TWW + FS
TWW + Control
TWW + CS
TWW + Control
TWW + CS
TWW + FS
Naji K. Al-Mefleh and O’badah F. Al-RajaImpac t of irrigation water quality and envelop e materials
Water and Environment Journal 0 (2018) 1–11 © 2018 CIWEM.4
The corn plants were irrigated twice a week with either
FW or TWW. The quantity of irrigation water applied was
based on the potential ETo, which was computed from
the daily readings of evaporation from a class Apan and
then converted to volume as a function of the area of
the planted corn. The seed corn was inserted below the
soil surface at a depth of 5 cm. A single lateral line irri-
gated two rows of corn plants. The spacing between each
row of corn and the lateral line was 2 m, and the corn
seeds were set 20 cm apart. The corn seeds (Zea mays
va r. saccharata) were planted on June 20th, 2016. The
corn plants were harvested on October 11th, 2016. No
organic or chemical fertilizer was added before or after
planting, and no pesticides or herbicides were used.
Water quality
The two water resources in the field experiment were
FW and TWW. Fresh water (tap water) was obtained from
groundwater wells. These wells supply water to the Jordan
University of Science and Technology campus. Treated
wastewater came from the treatment plant for domestic
wastewater at the Jordan University of Science and
Technology. The treatment processes in the plant consist
of primary, secondary, and biological treatments. The
main parameters (pH, EC, Na, K, TSS, Fe, Mn, and Zn) of
water quality for each water type were analysed at the
Agricultural Research and Extension Center of the Ministry
of Agriculture, Jordan.
Emitter performance parameters
The initial emitter discharge for each lateral line was
measured in the field at two different operating pressure
levels (0.8 and 1.6 bar). Based on the measured data,
three initial parameters were calculated: average discharge
(Qavg), discharge coefficient (Kdin), and discharge exponent
(Xin). At the end of the season, the lateral lines were
removed from the soil and the final emitter characteristics
were estimated in the field to determine the final average
discharge (Qavg), final discharge coefficient (Kdfi), and final
discharge exponent (Xfi).
The initial and final average discharge values were
determined by dividing the summation of individual emit-
ter discharge by the total number of emitters. The initial
discharge exponent (Xin) for the newly installed GR emit-
ters and the final discharge exponent (Xfi) after finishing
the field experiment were estimated by using a formula
in Keller and Karmeli (1974) at operating pressures of Havg1
(1.6 bar) and Havg2 (0.8 bar). Similarly, the initial discharge
coefficient (Kdin) for the new GR emitters and the final
discharge coefficient (Kdfi) after finishing the field experi-
ment were estimated using a formula in Karmeli and Keller
(1974).
The main final parameters of the emitter characteristics
were the mean discharge of the emitter (Qavg), coefficient
of variation (CVfi), emission uniformity (EUfi), Christiansen
uniformity coefficient (CUfi), and coefficient of variation
(CVfi). The emission uniformity (EUfi) was determined by
using a Karmeli and Keller (1974) equation, while the final
Christiansen uniformity coefficient (CUfi) was determined
by using an equation in Christiansen (1942). The coefficient
of variation (CVfi) was determined by using a formula in
Bralts and Kesner (1983). Also, each lateral line was divided
into four sections, and the average discharge was esti-
mated for each sec tion to check which sec tion was affec ted
by clogging. In addition, the relation between yield and
emitter clogging was investigated for each section.
Corn yield and water use efficiency
The corn plants were harvested by using scissors and
the corn yield collected from each lateral was placed in
a separate paper bag (72 samples) and transported to
the laboratory to take the fresh weight. Then, the har-
vested samples were placed in an oven at 70°C for 48 h
to obtain the dry weight. The WUE (kg/ha/mm) was esti-
mated as the total dry weight per hectare divided by
the total amount of irrigated water applied in millimeter
depth for each treatment. The experimental treatments
were assigned in a randomized complete block design
with two types of water as the main plots, two envelope
materials as the subplots, and three replicates.
Statistical analysis
Data were analysed in a randomized split-plot design
with three replications. General linear model with the
SAS version 9.1.3 statistical package (SAS Institute, 2005)
was used for data analysis. Analysis of variance was
used to test the effect of each treatment on emitter
performance under subsurface drip irrigation at
P < 0.05. The means for each treatment were compared
using the least significant difference (LSD) at the 0.05
level of probability.
Results and discussion
Irrigation practices
This SDI experiment was carried out in the field from
June 1st to September 28th, 2016. The corn seeds were
planted on June 6th, 2016. The total volume of water
applied to the experiment was based on the potential
ETο from a nearby class Apan. The daily evaporation
varied from 5 to 12 mm. The total amount of pan evapo-
ration during the growing season was 714 mm. The
maximum pan evaporation value was 275 mm during
Impac t of irrigation water quality and envelop e materialsNaji K. Al-Mefleh and O’badah F. Al-Raja
Water and Environment Journal 0 (2018) 1–11 © 2018 CIWEM. 5
July 2016. The total potential ETο during the irrigation
period was 531 mm. The total amount of water applied
for each treatment was 31.1 m3. No rainfall occurred
during the growing season in which the treatments were
applied.
Water quality
Two types of water, FW and TWW, were used to irrigate
the corn seeds. The chemical characteristics of FW and
TWW are summarized in Table 2. The chemical water
quality parameters for FW and TWW were compared
with the water quality criteria for emitter clogging pro-
posed in previous studies (Nakayama and Bucks, 1991;
Capra and Scicolone, 2004). The present study found
that the pH value of FW (8.14) was lower than that of
the TWW (8.25). According to the water quality criteria
by (Nakayama and Bucks, 1991), these pH values for
both water types have severe potential to cause emitter
clogging, where the concentrations of TSS, Fe, and Mn
in FW and TWW (Table 2) have a lower clogging potential
and thus less effect on emitter performance. (Liu and
Huang, 2009) in their study found a very small differ-
ence in the concentration of Fe in FW and TWW and
that the presence of Fe had low clogging potential. On
the other hand, (Al-Mefleh et al., 2015) found that the
Fe concentration in FW had medium clogging potential,
whereas that in TWW had severe clogging potential that
would adversely affect emitter performance. However,
according to (Capra and Scicolone, 2004), only an EC
value of 0.62 dS/m for FW and 1.8 dS/m for TWW posed
a moderate potential risk of emitter clogging.
Initial values of emitter characteristics
The initial values of the characteristics of the newly
installed GR emitters considered in this study average
discharge (Qavg), discharge coefficient (Kdin), discharge
exponent (Xin), coefficient of variation (CVin), emission
uniformity (EUin), and Christiansen uniformity coefficient
(CUin) are shown in Table 3. The Kdi was estimated for
the new GR emitters using FW at a pressure level of
0.8 bar. The lateral lines, which were buried under the
soil surface, were taken out of the soil in order to evalu-
ate the emitter performance characteristics. Figure 2 gives
the final discharge coefficient (Kdfi), values which were
estimated at the same pressure in the field for each com-
bination of water type (FW and TWW) and envelope mate-
rial (CS, FS, and CO) at the end of the field experiment.
As regards the Kdin (8.59), the rate of decrease based
on the Kdfi value was 7, 9, and 65% for FW with CS, FS,
and CO, respectively, while it was 10, 12, and 68% for
TWW with CS, FS, and CO, respectively.
The initial and final discharge exponents (Xi and Xfi)
were estimated at two different pressure levels (0.8 and
1.6 bar). Figure 3 illustrates the final discharge exponents
for each combination of water quality type and envelope
material. With respect to the Xin (0.46), the rate of increase
in the Xfi value for FW obtained with CS, FS, and CO was
9, 15, and 22%, respectively. The rate of decrease in Xfi
for TWW obtained with FS was 4%, whereas it increased
with CS and CO by 24 and 30%, respectively. Generally,
the value of the discharge exponent (X) characterizes
the flow regime and discharge versus the pressure
Table 2 Chemical water quality parameters for FW and TWW
Parameter Unit FW TWW
Clogging potential limit
of drip emitters
according to (Bucks
et al., 1979)
Low Moderate High
pH 8.14 8.25 <7.0 7.0–8.0 >8.0
EC dS/m 0.62 1.8 – – –
TSS ppm 21 40 <50 50–100 >100
Fe ppm 0.006 0.006 <0.2 0.2–1.5 >1.5
Mn ppm 0.002 0.002 <0.1 0.1–1.5 >1.5
Zn ppm 0.254 0.106 – – –
K % 0.012 0.0009 – – –
Na % 0.150 0.0169 – – –
Table 3 The initial of emitter characteristics for new emitters
Emitter characteristics New emitters
Qavg (L/h) 7.68
Kdin 8.59
Xin 0.46
CVin 0.04
EUin 94.64
CUin 96.40
Fig. 2. The values of discharge coefficient (Kdfi) at different water qualities
for fresh water (FW) and treated wastewater (TWW) at different envelope
materials of coarse sand (CS) and fine sand (FS).
Naji K. Al-Mefleh and O’badah F. Al-RajaImpac t of irrigation water quality and envelop e materials
Water and Environment Journal 0 (2018) 1–11 © 2018 CIWEM.6
relationship of the emitter. The lower the value of X, the
less the discharge is affected by variation in pressure.
According to (ASAE, 1985), the results of this study indi-
cate that the X value lies in the range of 0.4–0.6 (from
vortex flow to mostly turbulent flow). Lower emitter dis-
charge exponents are an indication of less susceptibility
to pressure changes. Thus, it can be concluded that the
discharge sensitivity to pressure variation in the presence
of a CS and a FS envelope material is low.
Average discharge
The main effect of both types of water, FW and TWW,
on emitter discharge was significant (P > 0.05). The main
interaction effect of water quality type and envelope
material on average discharge was also significant
(P > 0.05). The average emitter discharges for different
water types (FW and TWW) with different envelope
materials are presented in Fig. 4. With respect to the
initial emitter discharge (7.68 L/h), the rate of decrease
in emitter discharge for FW with CS, FS, and CO was
7.16, 9.6, and 65.5%, respectively. As for TWW, the Qavg
values obtained with CS, FS, and CO were 6.78, 6.84,
and 2.35 L/h, respectively. With respect to the initial
emitter discharge (7.68 L/h), the rate of decrease in
emitter discharge for TWW with CS, FS, and CO was
11.7, 10.9, and 69.4%, respectively. The mean values of
emitter discharge were not significantly different
between CS and FS, but they were significantly different
from the mean discharge with the CO treatment. These
results indicate that using envelope materials can
decrease the clogging potential in SDI emitters. The
results also show that the highest Qavg (5.58 L/h) was
obtained for FW compared with the Qavg (5.32 L/h) for
TWW. With respect to the initial emitter discharge (7.68
L/h), the rate of decrease in Qavg was 27 and 30% for
FW and TWW, respectively. This is likely due to the
high values of EC, TSS, and pH in TWW. This finding is
consistent with (Liu and Huang, 2009), who found that
emitter discharge is affected by the water quality of
FW, treated sewage effluent (TSE), and emitter type.
Also, the average discharge differs with emitter type,
water quality, and operational time. Another study
(Al-Mefleh et al., 2015) found that the effect of water
quality type (FW and TWW), operational time, and type
of emitter on emitter discharge was not significant.
Each lateral line was divided into four sections (sec1,
sec2, sec3, and sec4), and each section contained eight
emitters. Figure 5 gives the emitter discharge data for
each section for different water types and envelope mate-
rials. These findings are consistent with (Ravina et al.,
1997), who found that emitter discharge generally
decreases from the beginning to the end of a lateral line
due to pressure loss. In the present study, the trend line
of the Qavg over the combinations of TWW with CS and
FS decreased from sec1 to sec4. Under the combinations
of TWW with control and FW with CS, the Qavg in sec3
was higher than in sec2. Under FW with FS, the Qavg in
sec3 and sec4 was almost the same, while under FW with
CO it was unchanged in all sections. However, it was found
that both FW and TWW with CO produced the lowest Qavg
in all sections, compared with the other treatments.
Coefficient of variation
The CV values of the emitters for FW and TWW with
different envelope materials (CS and FS) are shown in
Fig. 6. The main interaction effect of water quality type
Fig. 3. The discharge exponent (Xfi) at different water qualities for fresh
water (FW) and treated wastewater (TWW) at different envelope materials
of coarse sand (CS) and fine sand (FS).
Fig. 4. The average emitter discharge (Qavg) at different water qualities for
fresh water (FW) and treated wastewater (TWW) at different envelope
materials of coarse sand (CS) and fine sand (FS).
Impac t of irrigation water quality and envelop e materialsNaji K. Al-Mefleh and O’badah F. Al-Raja
Water and Environment Journal 0 (2018) 1–11 © 2018 CIWEM. 7
and envelope material on the CV was not significant
(P > 0.05). However, the main effect of the water quality
type on the CV was significant (P > 0.05). The results
show that the highest final CVfi (0.10) was obtained under
TWW compared with a CVfi (0.06) for FW. With respect
to the initial CVin (0.04), the rate of increase in CVfi was
60 and 125% under FW and TWW, respectively. The main
effect of the envelope material on the CV was significant
(P > 0.05). The mean values of CVfi did not differ between
CS and FS but did differ from the mean value of CVfi
under CO.With respect to the initial CVin (0.04), the rate
of increase was 25% for CS and 250% for CO, whereas it
decreased under FS by 10%.
Özekici and Sneed (1995) classify CV values of <5% as
excellent, 5–7% as average, 7–11% as marginal, 11–15% as
poor, and >15% as unacceptable. According to this clas-
sification, the results of this study indicate that the CVfi
values for emitters under FW and TWW with CS are excel-
lent, whereas those under TWW and FW with FS are
average. (Solomon, 1979) classifies CV values of <3%, 5–7%,
8–10%, 10–15%, and >15% as excellent, average, marginal,
poor, and bad, respectively. Therefore, according to this
classification, the values of CVfi in this study ranged from
average to marginal. Another study (Bralts, 1986) classi-
fies CV values of 0–10%, 11–29%, and >29% as good, mod-
erate, and poor, respectively. So, according to this
classification, the values of CVfi in this study ranged from
good to moderate. Another classification (ASAE, 2003)
of CV values considers that <10% is good, 10–20% is mod-
erate, and >20% is poor. Other studies (Al-Mefleh et al.,
2015; Liu and Huang, 2009) have tested the impact of
FW and TWW on emitter performance and found that
CV values fall into the moderate or poor class.
Emission uniformity
Emission uniformity is one of the most frequently used
design criteria for trickle irrigation systems. It is one of
the indices for the evaluation of microirrigation perfor-
mance that is recommended by the ASAE Standards (ASAE,
2003). The main interaction effect of water quality type
and envelope materials on emission uniformity (EUfi) was
not significant (P < 0.05). However, the main effect of
water quality type (TWW and FW) on the EUfi was sig-
nificant (P > 0.05). The EUfi of the emitter values for FW
and TWW with CS, FS, and CO is provided in Fig. 7. The
results show that the highest mean value for EUfi (91.78%)
was obtained under FW compared with a mean EUfi value
of 86.78% for TWW. With respect to the initial EUin (94.64%),
the rate of decrease in EUfi was 3 and 8% under FW and
TWW, respectively. The main effect of the envelope mate-
rial on EUfi was also significant (P > 0.05). The mean values
of EUfi were not significantly different between CS and
FS, but they were significantly different from the mean
value of EUfi with the CO treatment. With respect to the
initial EUin (94.64%), the rate of decrease in EUfi was 0.9,
0.5, and 15% under CS, FS, and CO, respectively.
A comparison of EU at different water qualities FW
and TWW at different envelope materials of CS, FS, and
CO with other classifications (Keller and Bliesner, 1990;
ASAE, 1994; Capra and Scicolone, 1998; Li et al., 2009)
is presented in Table 4. According to these classifications,
the EUfi values of the emitters under TWW and FW with
FS and CS were high, where it was moderate under the
TWW with CO treatment. On the other hand, (Al-Mefleh
et al., 2015) found that the EU for GR emitter discharge
Fig. 5. Average emitter discharge (Qavg) for each section at different
water qualities types for fresh water (FW) and treated wastewater (TWW)
at different envelope materials of coarse sand (CS) and fine sand (FS).
Fig. 6. The coefficient of variation (CV) of the emitters values at different
water qualities for fresh water (FW) and treated wastewater (TWW) at
different envelope materials of coarse sand (CS) and fine sand (FS).
Naji K. Al-Mefleh and O’badah F. Al-RajaImpac t of irrigation water quality and envelop e materials
Water and Environment Journal 0 (2018) 1–11 © 2018 CIWEM.8
under TWW and FW varies from low to moderate. The
results of this study indicate that the two envelope mate-
rials (CS and FS) can be used under FW and TWW to
increase the emission uniformity. Moreover, it was found
that an increasing CV value leads to a decreasing EU
value, which is consistent with the results reported in
(Hezarjaribi et al., 2008). However, the results of the cur-
rent study showed that using envelope materials under
subsurface drip irriagation is recommended because the
EUfi under both CS and FS are high.
Christiansen uniformity coefficient
A low CU value indicates that water loss due to deep
percolation may be large if adequate irrigation is applied
to all areas. In this study, the main interaction effect of
water quality type and envelope material on CUfi was
not significant (P > 0.05). The CUfi values of the emitters
under FW and TWW with different envelope materials(CS
and FS) are presented in Fig. 8. The results show that
the highest mean value of CUfi (94.88%) was obtained
under FW compared with a mean CUfi value of 92.55%
for TWW. With respect to the initial CUin (96.40%), the
rate of decrease in CUfi was 1.6% and 4% under FW and
TWW, respectively. The main effect of the envelope mate-
rial on CUfi was significant (P > 0.05). The mean values
of CUfi were not significantly different between CS and
FS, but they were significantly different from that for
CO. With respect to the initial CUi n (96.40%), the rate of
decrease in CUfi under CS, FS, and CO was 0, 0.4, and
8%, respectively. With respect to the CU values under
the control treatment, the results indicate that the CUfi
performance for envelope materials as CS and FS was
high. (Keller and Bliesner, 1990) classify CU values for a
line source as follows: <75% is low, 75–84% is moderate,
and >84% is high. Based on this classification, the CUfi
values for emitters under TWW and FW with FS and CS
in this study fell into the highest category. (Liu and Huang,
2009) report that a CU greater than 98% under FW for
turbulent flow and the online pressure-compensation
type of emitter was obtained during an experimental
duration of 1188 hours, whereas it was 86.3% under TSE
for the same conditions. (Al-Mefleh et al., 2015) found
that the CU values for GR emitters under FW and TWW
vary from 68 to 94% and 73 to 92%, respectively.
Effect of water types and envelope material on
corn yield
The interaction effect of water quality and envelope
material on DMY was significant (P > 0.05).The DMY
results under different water quality types and envelope
materials are presented in Fig. 9. The average DMY was
1670.96 kg/ha for FW compared with 1422.27 kg/ha for
TWW. With respect to the DMY under FW, the DMY
Fig. 7. The emission uniformity (EU) of the emitters values at different
water qualities for fresh water (FW) and treated wastewater (TWW) at
different envelope materials of coarse sand (CS) and fine sand (FS).
Table 4 Comparison of EU at different water qualities FW and TWW at
different envelope materials of CS, FS and CO with other classifications
(Keller and Bliesner, 1990; ASAE, 1994; Capra and Scicolone, 1998, Li
et al., 2009)
Water types
Envelope materials TWW FW
CS 93*** 95***
FS 92*** 96***
CO 75** 85***
**Value between (70–80%) is moderate.
***Value between (80–100%) is high.
Fig. 8. The Christiansen uniformity coefficient (CU) of the emitters
discharge values at different water qualities for fresh water (FW) and
treated wastewater (TWW) at different envelope materials of coarse sand
(CS) and fine sand (FS).
Impac t of irrigation water quality and envelop e materialsNaji K. Al-Mefleh and O’badah F. Al-Raja
Water and Environment Journal 0 (2018) 1–11 © 2018 CIWEM. 9
under TWW was 15% less than that produced under
FW. The decrease in yield produced under TWW com-
pared to FW could be explained by the decrease in the
average emitter discharge. Under the combinations of
each water quality type (FW and TWW) with CS and
FS, the mean values of DMY were not different from
each other, but they were different from those for TWW
and FW with CO. Camp (1998) reports that, in many
cases, SDI produces greater crop yields than other irri-
gation methods. Similarly, (Lamm et al., 2002) state that
SDI enhances plant growth, crop yield, and quality.
Hence, this study recommends using FW with CS as
an envelope material in SDI to obtain a significant increase
in corn yield.
Water use efficiency
Water use efficiency was estimated as the dry weight of
corn per hectare divided by the water irrigation amount
in millimeter depth for each treatment. The interaction
effect of water quality type (FW and TWW) and envelope
material (CS and FS) on WUE was significant (P > 0.05).
The results for WUE under different water types and
envelope materials are presented in Fig. 10. The mean
values of WUE under each water type and envelope mate-
rial were not different from each other, but they were
different from those for TWW and FW with CO. Compared
to the combination of FW with CO, the rate of increase
in WUE was 635 and 226% under FW with CS and FW
with FS, respectively. With respect to the combination
of TWW with CO, the rate of increase in WUE was 474
and 221% under TWW with CS and TWW with FS, respec-
tively. The highest mean value of WUE was achieved by
using a combination of FW with CS while the lowest was
obtained under FW with CO. Similar to other studies (Ertek
et al., 2004; Kumar et al., 2007), this study found that
increasing the amount of irrigation water led to a decrease
in the WUE values and an increase in the crop yield.
Hence, the present study shows that FW with CS can
increase WUE. This is probably because the average emit-
ter discharge in FW with CS was higher than that under
TWW with CS, leading to a reduction in the emission
uniformity under TWW with CS treatment.
Conclusions and recommendations
1. The main interaction effect of water quality type and
envelope material on the coefficient of variation (CV),
Christiansen uniformity coefficient (CU), and emission
uniformity (EU) was not significant (P < 0.05).
2. However, these two factors had a significant effect on
average emitter discharge (Qavg), dry matter yield (DMY),
and water use efficiency (WUE).
3. The Qavg, emitter discharge coefficient (Kd), EU, and CU
values were greater under the fresh water (FW) with
(coarse sand (CS) and fine sand (FS)) treatment than
under the treated wastewater (TWW) treatment with
both CS and FS.
4. Under FW with CS and FS, the values of the discharge
exponent (X) and CV were lower than those under TWW
with CS and FS.
5. Thus, the results of this study indicate that FW with CS
can be used successfully to improve emitter
performance.
6. The CV values for Qavg under TWW with control were
higher than those for FW with CS and with FS.
7. Despite the water types, CS and FS around the lateral
lines increased DMY and WUE under the subsurface drip
irrigation.
8. While the highest values of DMY and WUE were obtained
at FW with CS, because the clogging potential under FW
Fig. 9. Dry matter yield (DMY) for corn under two water quality types
fresh water (FW) and treated wastewater (TWW) at different envelope
materials of coarse sand (CS) and fine sand (FS).
Fig. 10. Water use efficiency (WUE) under under two water quality types
fresh water (FW) and treated wastewater (TWW) at different envelope
materials of coarse sand (CS) and fine sand (FS).
Naji K. Al-Mefleh and O’badah F. Al-RajaImpac t of irrigation water quality and envelop e materials
Water and Environment Journal 0 (2018) 1–11 © 2018 CIWEM.10
is less than that under TWW, it leading to an increase in
the emission uniformity.
9. Further studies should be conducted on the effect of
emitter discharge and lateral depth under different
envelop materials (wick, sponge, sieves) on the emitter
performance charactersitics.
Acknowledgment
The authors would like to express their gratitude to the
Jordan University of Science and Technology for their
financial support for this experiment. The authors have
declared no conflict of interest.
To submit a comment on this article please go to http://
mc.manuscriptcentral.com/wej. For further information please see the
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