1

Effect of irrigation level on water distribution wetting patterns under drip and Kapillary

subsurface drip irrigation systems

Abass, M. E.1,2 and H., M. Al-Ghobari1

1Depart, of Agricultural Engineering, College of Food and Agriculture Sciences, King Saud University, Riydah 11451

Saudi Arabia. 2percision Agriculture Research Chair (PARC), Collage of Food and Agriculture Sciences, King Saud University,

Riydah 11451 Saudi Arabia.

Abstract:

Water in the Kingdom of Saudi Arabia, despite its environmental and climatic arid conditions, is the

key factor in the development processes. It is therefore considered that the main objective of this research is

to study the feasibility of saving water through the use of capillary irrigation with special emphasis on

studying the distribution pattern of soil moisture content in the soil under subsurface irrigation systems.

Experiments were designed for two levels of irrigation 4 Liter/h for two hours of application time (Level1 -

100%) and for one hour (Level2 - 50%). The field was divided into 3 major treatments: surface drip,

kapillary irrigation system at depth 25 cm and subsurface drip irrigation at 25cm. moisture measuring device

was used to measure soil moisture content in a grid form: vertically at four depths from and horizontally at

four distances from the emitters. Simulation of wetting patterns showed that the deep percolation in the SIS

was more than in KISSS and DIS, where the volumetric water content at a depth of 50 cm in the DIS (for

example) was 38-40%. While for the SIS was 45-48%, and for the KISSS was 20-18%.

Introduction:

Drip irrigation, also known as trickle

irrigation or microirrigation, is an irrigation method

which saves water and fertilizer by allowing water

to drip slowly to the roots of plants, either onto the

soil surface or directly onto the root zone, through a

network of valves, laterals, tubing, and emitters.

Crop yields can increase through improved

water and fertility management and reduced disease

and weed pressure. When drip irrigation is used

with polyethylene mulch, yields can increase even

further (Najafi, 2009). Advantages of surface drip

irrigation included on studies by (Tom, and Kenny,

2003) and also experiments by (Lawrence, and

Blaine, 2007) Smaller water sources can be used

because the Surface drip irrigation has lower

evaporative losses than surface, sprinkler, or micro

sprinkler irrigation because surface drip systems

wet a smaller surface area.

Design and management are closely linked

in a successful SIS system. Research studies and

on-farm producers both indicate that SIS systems

result in high-yielding crops and water-conserving

production practices only when the systems are

properly designed, installed, operated and

maintained (Rogers and Lamm, 2009) . Where

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(Juan, 2001) reported that the success of a

subsurface irrigation system (SIS) system for row

crops for example depends on: design, installation,

operation, management and maintenance. Camp,

(1998) and (Behrouz, et al. 2007) illustrated that

Subsurface irrigation system has a higher

susceptibility for decreasing the loss of water by

evaporation, runoff, and deep percolation in

comparison to other irrigation systems that supply

water to the soil surface. In addition, the high cost

of traditional drip irrigation systems, due to annual

replacement of system components, is substantially

reduced when subsurface components are

permanently installed below the soil tillage zone.

Jan, and Kristen, (2011) reported that the

kapillary irrigation subsurface system textile

irrigation is the new generation irrigation

technology providing intelligent water saving

solutions for recreational spaces and sports fields.

KISSS, installed underground, moves water

upwards and outwards to the root zone at the soils

natural absorption rate, effectively wetting large

areas of soil with even distribution. Through this

process, KISSS reduces water usage by eliminating

water evaporation, overspray, and runoff. William,

et al. (2008) found that (KISSS) applied water

directly to the root zone of plants with a minimum

of water loss through runoff, evaporation and deep

drainage. In this system, water is applied below the

ground surface directly to the plants roots area,

resulting in a significant improvement in water

application over traditional drip irrigation system.

Also, since the water is applied below the surface,

the water wastage due to evaporation is almost

eliminated.

Soil Moisture Wetting Patterns:

Designing and planning trickle irrigation

without enough information from moisture

distribution information from moisture distribution

in the soil do not result in the correct result. (Singh,

et, al 2006) mentioned that the information on

depths and widths of wetted zone of soil under

subsurface application of water plays the great

significance in design and management of

subsurface irrigation System (SIS) for delivering

required amount of water and chemical to the plant

Distance of outlets, discharge rate, and time of

irrigation in drip irrigation have to determine so that

volume of wetted soil is close to volume of plant's

root as much as possible.

Due to increasing computer speed and the

availability of more comprehensive numerical

models for simulating flow in variably saturated

soils, numerical approaches are now increasingly

being used for evaluating water flow in (SIS) or

(DIS) (Taghavi et al.1984) and (Angelakis et al.

1993). Several recent studies used for this purpose

the two-dimensional version of HYDRUS as

(Giuseppe, 2007) and (Mohammad, et, al 2011) or

three dimension software SURfer10 software as

(Kekkonen, et, al 2010).

Liga and Slack (2004) used HYDRUS-2D

to estimate the wetting pattern for subsurface drip

irrigation, but did not compare the results of

HYDRUS-2D simulations with actual experimental

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data. (Skaggs et al. 2004) carried out an extensive

analysis of multiple subsurface drip irrigation field

experiments, and successfully compared observed

wetting patterns with HYDRUS-2D model

predictions. (Lazarovitch et al. 2005) implemented

into HYDRUS-2D a new, system-dependent

boundary condition that considers source

properties, inlet pressure, and effects of the soil

hydraulic properties on calculated subsurface

source discharge and validated resulting code

against transient experimental data.

Material and Methods:

Research field experiments were conducted

on a 26 by 11 m plot located in the educational farm

of the College of Food and Agriculture Sciences,

King Saud University, Riyadh, Saudi Arabia on

Latitude N: 24ᵒ 44 11 and Longitude 46ᵒ 37 04.

Experiment Layout:

Three irrigation systems were used

on experiment: Surface Drip Irrigation (SDI),

Subsurface Irrigation System (SIS) and Kapillary

Irrigation Subsurface System (KISSS). The lateral

lateral for (SIS) and (KISSS) installed at 25cm

depth from soil surface, while the lateral of (DIS)

will be laid on the ground surface. That means the

field divided by five main plots (DIS, SIS25 and

KISSS25). Each system were designed and installed

for each field plot with laterals. Each plot consists

of three laterals lines, with length of 3 m. The

laterals were connected to PVC sub main laterals,

which were connected to galvanize steel main line.

The main line, sub main line and lateral lines are

placed above or the ground surface according the

irrigation system used in the study. These main

plots were replicate three times, as shown on (figure

1).

Water irrigation applied:

Two levels of irrigation will be

applied to the plots 100% of full irrigation that

required for irrigated vegetable crops by the three

irrigation systems (symbolized by I100) and 50% of

full irrigation that required for the crops

(symbolized by I50). These two level irrigation was

applied depending on the time required to irrigate

vegetable crops per day under drip irrigation

system. On irrigation level 100% (I100) were

irrigated 2hours, and on irrigation level 50% (I50)

were irrigated 1hour. Rate of irrigation on emitters

was (4L/h) on pressure (1.5) bar.

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Fig. 1: Experiment field layout

Fig. 2: The depths and distances from emitter and emitter line to measure soil moisture contents

Soil moisture content measurements:

Soil moisture content will be measured at

the various depths by using soil moisture sensor

called Waterscout SM 100 Soil Moisture Sensor

this sensor will measure Soil Moisture content with

little or no disturbance to the root zone. The thin

shape and pointed tip allows for easy insertion into

the soil or growing medium. Maintaining a healthy

water balance is essential for producing high quality

plants.

The soil moisture contents were determined

at different distances parallel to the lateral line ( 0,

10, 25 cm) and various depths perpendicular from

the emitter line (7.5, 20, 30 and 50 cm), as shown

in (figure 2). The soil moisture was measured at

each depth (7.5, 20, 30 and 50 cm) and was

repeated tow times (24, 48h) after irrigation were

determining the patterns of soil moisture

distribution resulting from each irrigation system.

Simulated wetting patterns:

Foe simulated soil moisture wetting

patterns were used SURFER10 computer software.

Surfer is a grid-based mapping program that

interpolates irregularly spaced (XYZ) data into a

regularly spaced grid. And for this purpose by

SURFER10 was used kriging model. Kriging is a

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geostatistical gridding method that has proven

useful and popular in many fields. This method

produces visually appealing maps from irregularly

spaced data. Kriging attempts to express trends

suggested in your data, so that, for example, high

points might be connected along a ridge rather than

isolated by type contours (Eddie, 2007).

Statistical analysis:

Experiment field divided to 3 main plots

DIS, SIS25 and KISSS25. Also there was 2 sub-plots

for irrigation level 50, 100%. In addition there was

2 Sub-Sub-plot for elapse time measurement. Al

this main plots, sub- plot and sub- sub plot was

replicated three times. For these divisions was used

split- split plot design. For this purpose was used

Costat computer software.

Result and Discussion:

The wetting patterns of soil moisture

content for KISSS generally showed that the KISSS

had higher soil moisture content than SIS,

especially near surface 9 above the laterals,

although the difference significant showed under

laterals. A study by (Viola, 2008) observed that the

soil water content was consistently higher in the

KISSS compared with the conventional SIS. The

result showed that on KISSS saved water at depth

10 and 15 cm long time, where the VWC at depth

10cm was 42,43% at 24h after irrigation as shown

in (Figure 3-a) while at same depth the VWC at 48h

after irrigation within 39, 40%, as shown in (Figure

-b).

Fig. 3: Soil moisture wetting patterns of Kapillary Irrigation Sub-Surface System (KISSS25) at 50%

Irrigation Level, (a) 24h, and (b) 48h after irrigation

a b

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For tube depth at 25cm the SIS and KISSS

showed that there was different in moisture content

at 24h after irrigation and SIS at pipe depth 25cm

(Figure 4 a,b) where the moisture content in SIS is

a more deep percolation than KISSS. Volumetric

water content at depth 40cm for example in SIS

were 32-34% where for KISSS were 22-23% ,

however at depth 50cm the moisture content in

SIS was 36-38% but in KISSS was less than 20%.

From (Figure 3 a,b) and (Figure 5a,b) the

study showed that the moisture content in the

kapillary irrigation system KISSS is concentrated

near the surface of the soil to depth 25 cm. This

depth near surface is very important for crops,

where (Evans, et, al. 1996) remarked that water

uptake by a specific crop is closely related to its

root distribution in the soil. About 70 percent of a

plant's roots found in the upper half of the crop's

maximum rooting depth. Deeper roots can extract

moisture to keep the plant alive, but they do not

extract sufficient water to maintain optimum

growth. When adequate moisture is present, water

uptake by the crop is about the same as its root

distribution. Thus, about 70 percent of the water

used by the crop comes from the upper half of the

root zone. This zone is the effective root depth.

Fig. 4: Soil moisture wetting patterns of Subsurface Irrigation System (SIS25) at 50%Irrigation Level, (a)

24h, and (b) 48h after irrigation

a b

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Fig. 5: Soil moisture wetting patterns of Kapillary Irrigation Sub-Surface System (KISSS25) at 100%

Irrigation Level, (a) 24h, and (b) 48h after irrigation

At a distance 25cm and depth 7.5cm

point B (25,7.5) the study showed that the mean soil

water content for KISSS25 was 47.954% for DIS

25.22% , while LSD were 1.1637 in 0.05

Significance level. Decreasing on soil water content

at this depth 7.5cm on DIS showed that there were

lost on water due to evaporation. But the decline in

the moisture content in SIS may be because wetted

patterns move in vertical direction more than

horizontal direction. In addition the plastic tape

glued on the geo-textile above the emitters deflects

the discharged water and prevents tunneling into the

surrounding soil. (Philip and Charlesworth, 2003)

also mentioned that on KISSS the wetting pattern

has been enhanced by the addition of plastic

barriers beneath the drip line.

Simulated wetted width and depth was

affected by discharge rates of laterals. With

increasing discharge rates of laterals depths and

width of wetted patterns soil increased. (Goldberg

and Shmueli 1970) was indicated that the rate of

horizontal direction.

The result shows that SIS25 induced higher

significant (P<0.01) at point B(0,30) than other

system irrigation . However the KISSS25 at 50%

level of irrigation and at 48h after irrigation was

given same values for DIS (Figure 6) at 100%

amount of water after 24h from applied irrigation.

The result showed that the lowest mean values of

moisture content were measured on DIS at I50 after

24h from applied irrigation. From Table (1) the

result also illustrated that there is significant

between kapillary irrigation subsurface system

where found the KISSS25 at I50 is higher than

KISSS15 at I100 after 48h from irrigation.

a b

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Fig. 6: Soil moisture wetting patterns of Drip Irrigation System (DIS) at 100%Irrigation Level, (a) 24h, and

(b) 48h after irrigation

B(0,20) B(10,20) B(15,20) B(25,20)

24h 48h Aver 24h 48h Aver 24h 48h Aver 24h 48h Aver

a b

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Table (1) Effect of amount of water and elapsed time on irrigation system at depth 20cm

The result showed that at depth 50cm

underground the SIS25 achieved high significant

(P<0.05) compared with other system. As shown in

Table (2) at point B(0,50) subsurface irrigation

system when installed tube at depth 25m induced

high value of moisture content more than it at

15cm depth tube. Result also showed that the

KISSS25 at the 50% level of irrigation at 48h. The

result also indicated that at point B(0,50) commonly

there is no- significant (P ≤ 0.1343) for irrigation

level and elapse time - 0.05 significance level- to

irrigation system. Also result at this point showed

that there is no-significant (P ≤ 0.1152) for amount

of water on elapsed time for kapillary irrigation

subsurface system as shown in (figure 5).

Fig. 7: Soil moisture wetting patterns of Drip Irrigation System (DIS) at 50%Irrigation Level, (a) 24h, and

(b) 48h after irrigation

Table (2) Effect of amount of water and elapsed time on irrigation system at depth 50cm

Dis L 50% 26.3 25.9 26.1 25.2 24.8 25.0 23.3 24.3 23.8 23.0 21.5 22.3

L100% 47.3 35.6 41.4 43.6 27.5 35.5 32.0 24.7 28.3 31.4 25.7 28.5

Average 36.8 30.7 33.8 34.4 26.1 30.3 27.7 24.5 26.1 27.2 23.6 25.4

SIS25 L 50% 27.5 23.8 25.7 22.9 22.2 22.6 22.8 22.7 22.8 21.8 19.0 20.4

L100% 40.6 36.9 38.8 39.2 32.6 35.9 41.9 33.8 37.9 38.8 31.7 35.3

Average 34.1 30.4 32.2 31.1 27.4 29.2 32.3 28.3 30.3 30.3 25.4 27.8

KISSS25 L 50% 53.7 49.2 51.4 52.5 48.9 50.7 53.0 48.1 50.5 51.5 45.9 48.7

L100% 63.1 54.6 58.8 62.2 53.5 57.9 60.4 51.8 56.1 60.4 52.1 56.3

Average 58.4 51.9 55.1 57.4 51.2 54.3 56.7 50.0 53.3 55.9 49.0 52.5

LSD

Is *IL 1.7591 1.1436 0.9782 0.8830

IL* Te 1.0745 1.0007 0.8571 0.8630

IL*I S *Te 2.4027 2.2377 1.9166 1.9297

a b

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B(0,50) B(10,50) B(15,50) B(25,50)

24h 48h Aver 24h 48h Aver 24h 48h Aver 24h 48h Aver

Dis L 50% 34.0 37.3 35.6 28.8 34.2 31.5 14.3 30.2 22.2 12.7 27.6 20.1

L100% 39.7 43.4 41.5 29.7 39.9 34.8 32.7 38.5 35.6 23.0 32.5 27.8

Average 36.8 40.3 38.6 29.3 37.0 33.2 23.5 34.3 28.9 17.9 30.0 23.9

SIS25 L 50% 41.3 44.9 43.1 35.5 43.4 39.5 30.7 39.0 34.9 31.2 29.6 30.4

L100% 48.1 51.7 45.9 46.7 41.3 44.0 48.1 35.9 42.0 40.1 35.2 37.7

Average 44.7 44.3 44.5 41.1 42.4 41.7 39.4 37.5 38.4 35.7 32.4 34.0

KISSS25 L 50% 14.5 22.9 18.7 14.4 20.0 17.2 14.5 18.4 16.4 14.9 20.8 17.9

L100% 15.8 21.7 18.7 15.3 20.4 17.9 14.9 16.7 15.8 14.9 19.1 17.0

Average 15.1 22.3 18.7 14.9 20.2 17.6 14.7 17.5 16.1 14.9 20.0 17.5

LSD

Is *IL 1.3072 2.4428 1.4357 1.1848

IL* Te 1.8390 2.2010 1.1442 0.9323

IL*I S *Te 4.1122 4.9215 2.5586 2.0846

There is significant for SIS at this point

B(0,50) for subsurface irrigation system at two depth

layout, where at SIS25 the moisture content was

increased when applied 100% amount of water at

48h. This result consist with (Dabral, et, al. 2012)

observed that wetting pattern is significant in

deciding depth of lateral placement below soil

surface, emitter spacing and system pressure for

delivering required amount of water to the plant.

The higher significant for SIS at depth 50cm

illustrated there a loss of water by a deep

percolation more than kapillary irrigation. At point

B(10,50) there is highly significant (P < 0.05) for

irrigation level and also there is significant for

measurement time 24, 48h after irrigation.

Fig. 8: Soil moisture wetting patterns of Subsurface Irrigation System (SIS25) at 50%Irrigation Level, (a)

24h, and (b) 48h after irrigation

Conclusions:

a b

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The result indicated that there were significant

differences between irrigation levels I50, I100 at

any irrigation systems. In addition there were

significant differences between the elapsed time

measurements of 24 and 48h after irrigation. The

best wetting patterns were typically observed in the

parallel direction, especially under the emitter, as

compared with the perpendicular direction,

especially in the kapillary irrigation subsurface

system. The plastic tape glued to the geo-textile

above the emitters at KISSS deflected the

discharged water and prevented tunneling into the

surrounding soil.

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