This document provides an overview of drip irrigation. It discusses the history of drip irrigation, which dates back to ancient Persia and includes early uses of clay pots and bamboo. Modern drip irrigation began in Israel in the 1950s and 1960s with early patents and experiments. It describes the basic principles and components of drip irrigation systems, including drippers, pipes, filters, and valves. The document covers topics such as water distribution in soil, filtration, fertigation, system design, and scheduling. Drip irrigation is presented as a comprehensive agro-technology that improves water and nutrient use efficiency compared to other irrigation methods. It has gained widespread use around the world for both field and greenhouse crops.

1. STATE OF ISRAEL
MASHAV CINADCO
MINISTRY OF FOREIGN AFFAIRS
CENTRE FOR INTERNATIONAL
COOPERATION
MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT
CENTRE FOR INTERNATIONAL AGRICULTURAL DEVELOPMENT
COOPERATION
DRIP IRRIGATION
SECOND EDITION
By
Moshe Sne
Irrigation Consultant and Former Director,
Irrigation and Soil Field Service
2005

2. I
CONTENTS
Chapter Topic Page
List of Tables II
List of Figures III
Foreword to The First Edition VIII
Foreword to the Second Edition IX
Acknowledgments X
1. Introduction 1
The History of Drip Irrigation 1
2. Principles of Drip Irrigation 4
Advantages and Limitations 5
3. The Distribution of Water in The Soil 8
4. The Drip System 14
5. Flow Rate – Pressure Relationship 18
6. Pipes and Tubes for Drip Irrigation 28
7. Dripper Types, Structure, Function and Properties 32
8. Accessories 40
9. Filtration 46
10. Fertigation 58
11. Water Quality 64
12. Monitoring and Control 71
13. Subsurface Drip Irrigation (SDI) 74
14. Family Drip Irrigation 80
15. Water Distribution Uniformity 82
16. Drip Irrigation of Crops 84
17. Basics of Drip System Design 93
18. Drip Irrigation Scheduling 106
19. Maintenance 112
20. References and Bibliography 116
Conversion factors 120

3. II
LIST OF TABLES
No. Page
1. Pressure Units 18
2. The Friction Coefficient ( C ) of Pipes 20
3. The Effect of Dripper Exponent on Head-Loss – Flow-
Rate Relationship
22
4. Head losses in Acuanet automatic valve 23
5. Plastro Hydrodrip II Integral Drip Laterals Technical
Data
24
6. PE Pipes for Agriculture 29
7. Internal Diameter and Wall Thickness of LDPE Pipes 29
8. Internal Diameter and Wall Thickness of HDPE Pipes 30
9. PVC Pipes for Agriculture 30
10. Internal Diameter and Wall Thickness of PVC Pipes 31
11. Flow-Rate of Spring Actuated Pressure Regulators 42
12. Characteristics of Water Passageways in Drippers
(example)
46
13. Screen Perforation - examples 47
14. Sand particle size and mesh equivalent 48
15. Nominal Filter Capacity – examples 50
16. Relative Clogging Potential of Irrigation Water in Drip
Irrigation Systems
65
17. Threshold and Slope of Salinity Impact on Yield 67
18. Yield Increase and Water Saving in Conversion From
Surface to Drip Irrigation
84
19. Manufacturer Data about the Allowed Lateral Length in
the Examined Alternatives
96
20 Allowed lateral length of Ram 16 PC drippers 97
21. Calculation Form: Head losses in pipes 101
22. Head Loss Calculation Form – Pressure Compensated
(PC) Drippers
103
23. Head Loss Calculation 105
24. Irrigation Scheduling – Calculation Form (example) 106
25. Irrigation Scheduling Form for Annuals 109
26. Operative Irrigation Schedule 111

4. III
LIST OF FIGURES
No. Page
1. Clay pot 1
2. Early patents issued for drip irrigation 2
3. Wetting pattern of drip irrigation in different soil textures 4
4. Water distribution in the soil along time 8
5. Water distribution from a single dripper in loamy and sandy soil 9
6. Salt distribution in the wetted volume 10
7. Leaching of salt into the active root-zone by rain 10
8. Diverse root systems 12
9. Typical root systems of field crops 13
10. Root system in drip irrigation vs. root system in sprinkler irrigation 13
11. Simplified scheme of drip system 14
12. Typical layout of drip irrigation system 15
13. Components of drip irrigation system 16
14. Control Head 17
15. Relationship between the dripper exponent and lateral length 22
16. Pressure Compensated dripper flow-pressure relationship 23
17. Non-pressure compensated flow-pressure relationship 23
18. Acuanet automatic valve 24
19. Head loss nomogram, based on Hazen-Williams formula 25
20. Nomogram for calculation of head losses in HDPE pipes 26
21. Nomogram for calculation of head losses in LDPE pipes 27
22. Evolution of the passageway style 32
23. Turbulent flow 33
24. Orifice dripper 33
25. Vortex dripper 33
26. Labyrinth button dripper 33
27. Tape dripper lateral: empty and filled with water 33
28. Point-source and line-source wetting by drippers 34
29. In-line laminar dripper and turbulent dripper 35
30. On-line drippers 35
31. Button drippers insert design 36

5. IV
LIST OF FIGURES (Continued)
No. Page
32. Adjustable and flag drippers 36
33. Flexible diaphragm under pressure 36
34. Button and inline PC drippers 36
35. ADI PC dripper 37
36. Change of water passageway length under high pressure 37
37. Woodpecker drippers 37
38. Flap equipped dripper 38
39. Arrow dripper for greenhouses, nurseries and pot plants 38
40. Six outlets 38
41. Ultra low flow micro-drippers 39
42. Integral filters 39
43. Auto flushing, pressure compensating dripper 39
44. Plastic and metal pipe and lateral connectors 40
45. Lateral start, plugs and lateral end 41
46. Reinforced connectors 41
47. Drip laterals connectors and splitters 41
48. Hydraulic valve 42
49. Spring pressure regulator assemblies 42
50. Spring actuated pressure regulator 43
51. Hydraulic pressure regulator 43
52. Horizontal and angular metering valves 43
53. Electric valve 44
54. Air-relief valves 44
55. Atmospheric vacuum breakers 45
56. Lateral-end flushing action 45
57. Screen filter 47
58. Head losses in clean screen filters 47
59. Disc filter 48
60. Media filter 48
61. Sand separator 49

6. V
LIST OF FIGURES (Continued)
No. Page
62. Hydro-cyclone sand separator – head losses and optimal flow rates 49
63. Self-flushing screen filter 52
64. Automatic flushing of disk filters 52
65. High capacity media filters array 53
66. Back-flushing of media filters 53
67. High capcity automatic filter 53
68. Compact automatic filter 54
69. Slow sand filter 55
70. Slow sand filter scheme 56
71. Treflan impregnated disk stack 57
72. Fertilizer tank 58
73. Venturi injector 59
74. Piston and diaphragm hydraulic pumps 59
75. No-drain hydraulic pump 59
76. Mixer 60
77. Electric pump 60
78. Check valve 63
79. Tandem backflow preventer - exploded 63
80. Tandem backflow preventer 63
81. Installed backflow preventer 63
82. Chlorine- distribution below and between drippers 68
83. Salt level in relation to distance from dripper 68
84. Water quality for irrigation 68
85. Tensiometers 71
86. Soil moisture capacitance sensor 71
87. Multi-factor simultaneous phytomonitoring 72
88. Scheme of SDI system 74
89. Wetting pattern in SDI 77
90. Burying SDI lateral 78
91. Three-shank SDI lateral burying machine 79
92. Bucket kit 80

7. VI
LIST OF FIGURES (Continued)
No. Page
93. Drum kit 80
94. "Netafim" Family Drip System (FDS) 81
95. Components of Family Drip System (FDS) 81
96. Treadle pump 81
97. Apple root system in well aerated soil 84
98. Apple root system in compact soil 84
99. Drip irrigation Layouts in orchards 85
100. Drip laterals in vineyard, hung on the trellis wire 85
101. Dripper layouts in pecan orchard 85
102. Typical shoot and fruit growth curves for peach and pear 86
103. Partial Root-zone Drying with two laterals per row 87
104. Mango grown on nutrition ditches vs. control 87
105. Mechanized deployment of drip laterals 88
106. Cotton root development 88
107. Laterals on top of hillocks in potatoes 89
108. Lateral between hillocks 89
109. Potatoes – one lateral per row 89
110. Wide-scale drip irrigation in greenhouses 91
111. Drip irrigation of potted plants in greenhouse 92
112. Roadside drip irrigation 92
113. Wetted volume in different soil types 94
114. Apple orchard map 95
115. Local head losses in accessories 98
116. Drip system layout scheme 99
117. Feasible layouts 100
118. Segmented drawing for head loss calculation 101
119. The chosen diameter for mainline and manifold 102
120. One manifold layout 103
121. Pressure compensated Ram 2.3 l/h dripper, one shift design 104
122. Melons plot map 104
123. Melons – In-line non-compensated drippers 105

8. VII
LIST OF FIGURES (Continued)
No. Page
124. Schematic wetting pattern in different textured soils 107
125. Different schedules of drip irrigation operation 108
126. Layout of drip system for 55 ha. Of cotton 110
127. Automatic line flushing valve 114
128. Punch and holder 115

9. VIII
FOREWORD TO THE FIRST EDITION
The need for a comprehensive and updated book on Drip Irrigation has long been felt
as reflected by the intensive scheduling of international irrigation courses in
CINADCO’s yearly training program. The booklet on Drip Irrigation written by
Elimelech Sapir, and the late Micha Shani, in 1976 was updated in the early 1990s
and is used extensively in CINADCO’s irrigation training courses, in Israel and
abroad. However, with the rapid expansion and technological advances of Israeli
irrigation equipment, it became apparent that more detailed and systematic literature
was needed.
Moshe Sne, the former Director of the Irrigation and Soil Field Service of the Israeli
Ministry of Agriculture and Rural Development, Extension Service, has been greatly
involved in the subject of irrigation systems and techniques in general, and drip
irrigation in particular, for many years. He has also served as the chief irrigation
course adviser for CINADCO. On the eve of his retirement from government service,
he committed himself to the worthy task of preparing a book on Drip Irrigation in
Israel.
We wish to thank the author for the great amount of work and effort he put into the
writing and compilation of the drip irrigation subject matter presented here. He was
greatly assisted by the leading irrigation companies in Israel who allowed the use of
pictures, charts, diagrams and figures. We wish to thank them and the many
professionals who assisted Mr. Sne in this project and are credited throughout the
book.
We are happy to share the professional material presented here with irrigation
experts, agriculturalists and others in the field, in countries throughout the world that
participate in Israel’s international cooperation programs. The contents have been
formulated particularly for the physical conditions prevailing in Israel. These are
recommendations only and should not take the place of local detailed irrigation
planning.
This is the first edition of Drip Irrigation printed in a limited number of copies. We
would appreciate your comments and suggestions for the coming editions.
Abraham Edery, Director of Training, CINADCO
Shirley Oren, Publications’ Coordinator, CINADCO
May 2004

10. IX
FOREWORD TO THE SECOND EDITION
A year has passed since the publication of the First Edition of Drip Irrigation written
by Moshe Sne. At the time of the first printing, we requested from the irrigation
experts, irrigation course participants and others who would be reading the book to
give us their comments and suggestions.
This was done and the author incorporated the comments and suggestions received,
as well as his own changes and corrections into this publication.
We are pleased to bring to print in May 2005 the second edition of Drip Irrigation. We
are greatly appreciative of the efforts made by Moshe Sne to improve upon and
correct the already comprehensive material he compiled previously.
As we mentioned in the Foreword to the First Edition, we are happy to share this
professional material with irrigation experts, agriculturalists and other interested
parties in countries throughout the world that participate in Israel's international
agricultural development programs. In order to facilitate this purpose, the book is
currently being translated into Spanish and Russian. The content has been
formulated particularly for the physical conditions prevailing in Israel. These are
recommendations only and should not take the place of local detailed irrigation
planning.
Abraham Edery, Director of Training, CINADCO
Shirley Oren, Publications' Coordinator, CINADCO
May 2005

11. X
ACKNOWLEGMENTS
I would like to thank my colleagues and friends, as well as the Irrigation course 2004
participants for proofreading the preliminary first edition and for the helpful remarks
and corrections. Their valuable contribution had been embedded in the current
Second Edition of the publication being printed in 2005.
I am deeply grateful to the authors of the books and papers cited in the Reference
List and the Bibliography. The vast material on drip irrigation inspired me and filled
me with admiration for the enthusiastic and hard-working people in the forefront of
irrigation technology. I would also like to thank the manufacturers for the wealth of
information embodied in their brochures and professional guides. I am particularly
grateful to Mr. Nachman Karu and Mr. Dubi Segal for their contribution of impressive
and useful graphic material.
Last but not least, thanks to Ms. Shirley Oren and Ms. Bernice Keren for their patient
editing and elaboration of the Second Edition of Drip Irrigation.
Moshe Sne
May 2005
AUTHOR'S NOTE
In the first version, uploaded to Scribd on September 19, some mishaps occurred
during the conversion from the print to the electronic version, mostly in matching
between the table of contents, and the actual document layout. These discrepancies
had been adjusted. Additionally, replacement of some outdated figures and minor
corrections and adjustments had been done in this version of the document.
The author
November 2009

12. DRIP IRRIGATION
1
Chapter 1. INTRODUCTION
Drip irrigation, by definition, is an irrigation technology. However, during the last four
decades, since the start of its world-wide dissemination during the early sixties, it
appeared not only as an irrigation technology but as a comprehensive agro
technology that changed crop growing practices and widened modern agricultural
horizons. Drip irrigation facilitated increased efficiency of water use in irrigation and
triggered the introduction and development of fertigation – the integrated application
of water and nutrients. It raised the upper threshold of brackish water use in irrigation
and simplified the harmonization of irrigation with other farming activities. Drip
irrigation facilitated optimal “spoon-feeding” of water and nutrients to crops, attuned
to the changing requirements along the growing season. Drip irrigation enabled the
accurate supply of water and nutrients to the active root-zone with minimal losses. In
protected cropping, it facilitated the combination of the advantages of hydroponics
with improved plant support by solid detached media. Drip irrigation has promoted
the sophistication of monitoring, automation and control of irrigation, as well as the
diversification of filtration technology. Drip irrigation has gained momentum during the
last two decades. The world-wide area under drip irrigation is estimated at 3 million
ha., out of a total area of 25-30 million ha. irrigated with pressurized irrigation
technologies. The area of surface irrigation is estimated at 270-280 million ha.
THE HISTORY OF DRIP IRRIGATION
From the early days of irrigated agriculture, farmers and irrigation professionals
looked after concepts and technologies to improve water utilization in agriculture.
One of these concepts was the localized application of water directly to the root zone.
Another concept was subsurface water application to avoid evaporation from the soil
surface.
Such technology was used by the ancient
Persians and is still applied in some countries in
Asia and Africa. Clay pots made of unglazed
indigenous earth-ware have many micro-pores in
their walls. These micro-pores do not allow water
to flow freely from the pot, but slowly release the
water in the direction in which suction develops by
the tension gradient. The pots are buried neck-
deep into the ground, filled with water and the
plants are planted next to them.
In south-east Asia, bamboo drip irrigation has been in use for more than 200 years.
Stream and spring water was tapped into bamboo pipes in order to irrigate
plantations. About 18-20 l/min of water that enters the bamboo pipe system flows
along several hundred meters and is finally distributed to each plant at a rate of 20-
80 drops per minute. This traditional system is still in use by tribal farmers to drip-
irrigate their black pepper plots.
The concept of water saving was further elaborated during the nineteenth century.
People involved with irrigation were dissatisfied with the wasteful surface irrigation
technologies. There is evidence that in 1860, subsurface tile pipes were used
experimentally for irrigation in Europe. Patents for water saving irrigation
technologies were registered in Europe and the United States. Patent # US146,572
dated January 20, 1874 by Nehemiah Clark of Sacramento, California, describes a
Fig. 1. Clay pot

13. DRIP IRRIGATION
2
pipe with a "non-clogging" leaking connection. In the year 1888, Mr. Haines of
Nashville, Iowa, registered a patent of the direct application of water to the root
system of orchard trees. In 1917, Dr. Lester Kellar introduced an agricultural drip
system in a symposium at Riverside, CA., but further development of drip irrigation in
the United States was delayed for another 40 years.
Perforated pipes for subsurface irrigation were used experimentally in Germany in
1920 and in the USSR in 1923. In 1926, Mr. Nelson of Tekoa, Washington, had
registered a patent for a subsurface irrigation system. Another subsurface irrigation
system was examined in 1934 at the New Jersey and Indiana Agricultural
Experiment Stations. After WWII, micro-tubes were used for greenhouse irrigation in
England and France. In 1954, Mr. Richard Chapin developed in the USA, drippers for
irrigation of potted plants in greenhouse. Mr. Hansen, of Denmark, developed a small
plastic tube for the irrigation of potted plants in greenhouses.
Fig. 2. Early patents issued for drip irrigation
The breakthrough in drip irrigation occurred in the early sixties, firstly in Israel and
later in the United States. This initiative is attributed to Mr. Simcha Blass, who
invented a dripper with long laminar water flow passageways in the form of a spiral
micro-tube. The micro-tube was first wrapped around the feeding lateral, followed by
an improved model comprised of a molded coupling with a built-in spiral. Later it was
manufactured as a two-piece in-line dripper (US patent 3,420,064).
Mr. Blass collaborated with Kibbutz Hazerim to establish "Netafim", a worldwide
leading drip irrigation company. At the same era another Israeli inventor, Mr. Ephraim
Luz developed a different drip irrigation system, with perforated polyethylene tubes, 4
– 6 mm in diameter. In both technologies the drip laterals were buried 20 – 40 cm
below the soil surface. The main flaw with the buried laterals was the clogging of the
drippers by soil particles and intruding roots. Mr. Yehuda Zohar, an agricultural field-
adviser demonstrated that on-surface drip irrigation had the same advantages as the
subsurface installation but with significantly less clogging hazard. For many years the
on-surface pattern was the dominant drip irrigation technology. During the late sixties
and early seventies, "Netafim" licensed some foreign factories of irrigation equipment
in the USA and South Africa to manufacture its patented drippers.
As mentioned before, in 1954, Mr. Richard Chapin of the United States developed a
system comprised of small diameters tubes for irrigation of pot plants in

14. DRIP IRRIGATION
3
greenhouses. In 1964, he invented a drip tape for the irrigation of cantaloupes. In
1974, he developed the bucket kit for irrigation of small family plots in developing
countries. That system does not require an external source of energy.
In 1962, Mr. S. Davis installed an experimental subsurface drip irrigation system in a
lemon orchard in Pomona, California, USA. Only ten years later, during the early
seventies, after the problems of root intrusion and soil particle suction had been
resolved, did the installation of subsurface drip irrigation (SDI) systems expand on a
wide scale in California and other States of the United States.
Hawaiian sugar producers were introduced to drip irrigation In 1970, at an agricultural
convention in Israel. Returning to Hawaii, they converted a significant portion of sugar
cane acreage to drip irrigation, with astounding achievements in both water savings
and sugar content.
In order to reduce the costs of the drip system, perforated thin-wall tapes were
introduced. However the variance in flow-rate and the clogging of the outlets were
unacceptable. These problems were solved with the introduction of a twin-walled
tape in which an inner conveyance tube bled water into a second outer distribution
duct that emitted water from tiny holes onto the ground at low flow rates. A ratio of
four outlet holes for every inner hole rendered low-flow rates with acceptable
emission uniformity.
Corresponding with the expansion of drip irrigation in the early sixties, fertigation
technology evolved. Due to the small volume of wetted soil in drip irrigation, an
adequate supply of nutrients to the root system requires the synchronization of water
and nutrient supply through the drip system.
Further steps in the development of drip irrigation technology was the introduction of
seep hoses, woodpecker drippers, compensated drippers, non-leaking (no-drain)
drippers, anti-siphon mechanisms and techniques that prevent root intrusion.
Drip irrigation triggered the development of filtration systems and chemical water
treatment technologies that were necessary to protect the narrow dripper water
passageways from clogging. Sophisticated control and monitoring instrumentation
has been developed to enable the optimal implementation of this technology.
Drip irrigation was also adopted by gardeners and landscape architects. It
revolutionized the concept of irrigation in gardening, with its capability to irrigate
without disturbing visitors. The utilization of reclaimed water with subsurface
installation and the convenience of irrigating narrow strips of vegetation without
wetting sidewalks, excited leading professionals in this sector. Nowadays there are
many countries where sales of drip irrigation equipment for landscaping and
gardening applications surpass those of agricultural applications.
Mainstream drip irrigation is relatively expensive and is actually unaffordable for low
income farmers in developing countries. This impediment has been partially solved
by local production of cheap low-quality drip equipment, which compromises on
emission uniformity and life expectancy. Another solution was the development of
simple drip kits, such as the bucket and drum kits, designed for small family-run
agricultural plots.

15. DRIP IRRIGATION
4
Chapter 2. PRINCIPLES OF DRIP IRRIGATION
Drip irrigation, sprinkler irrigation, center pivot and lateral-move are classified as
pressurized irrigation technologies. In pressurized irrigation, the driving force of water
movement is provided by an external energy source (or a raised reservoir). The water
is delivered through a closed pipe system. This differs from surface irrigation
technologies – flood, border, furrow and small basin irrigation – in which the driving
force of water flow is gravity, and the delivery and application structures – canals,
ditches, furrows, small ponds and basins – are open to the atmosphere.
Drip irrigation is a section of the micro-irrigation (localized irrigation) sector, which
includes also micro-sprayers and mini-sprinklers. The term trickle irrigation is
generally used to describe irrigation methods whereby small quantities of water are
applied at short intervals directly to the soil, from point source discrete emitters
spaced along thin tubes or tapes, line-source densely mounted dripper outlets, or
seep-hoses. Water applied from small sprayers, micro-sprinklers and bubblers is
transmitted to the soil through the atmosphere. The terms trickle, micro, drip, low
volume and localized irrigation are sometimes used interchangeably in the literature,
although each one has a slightly different technical meaning.
With micro-irrigation, the emitters deliver water through three different types of
emitters: drippers, bubblers and sprayers/micro-sprinklers. Drippers apply water as
discrete droplets or trickles. With bubblers, water ‘bubbles out’ from the emitters at
higher flow rates and the flow appears as a continuous stream. Micro-sprinklers
sprinkle, spray or mist water to the atmosphere around the emitters.
The uniqueness of drip irrigation is the partial wetting of the soil. Water is applied by
many tiny emitters, 5,000 – 300,000 per hectare. In on-surface installation, each
emitter moistens the adjacent surface area. The percentage of the wetted surface
area and soil volume depends on soil properties, initial moisture level of the soil, the
applied water volume and emitter flow rate. In subsurface installation, the soil surface
remains dry.
Fig. 3. Wetting pattern of drip irrigation in different soil textures
Adapted from: The University of Maine Cooperative Extension Farm Note
The lateral movement of the water beneath the surface of a medium or heavy
textured soil is more pronounced than in sandy soils. Whenever the dripper's flow
rate exceeds the soil intake (infiltration) rate and its hydraulic conductivity, the water
ponds on the soil surface and wets larger soil volume.
The vertical cross section of the wetted volume in sandy soils resembles a carrot. In
medium textured soil, the dimensions of the wetting depth and wetted diameter are

16. DRIP IRRIGATION
5
similar, while in heavy soils the horizontal dimension of the wetted volume is greater
than that of the wetted depth.
Indicative values for the wetted diameter by a single dripper may be 30 cm in a light
soil, 60 cm in a medium soil and 120 cm in a fine textured soil.
Due to the partial wetting of the soil in drip irrigation, water has to be applied more
frequently than with other irrigation methods that wet the entire area such as sprinkler
and flood irrigation.
The capacity to apply water to each plant separately in small, frequent and accurate
dosing enables high application efficiency. Water is delivered from the emitter
continuously in drops at one point, infiltrates into the soil and wets the root zone
vertically by gravity and horizontally due to capillarity.
During the last three decades, subsurface drip irrigation (SDI) has gained
momentum. The wetting pattern with SDI is somewhat different from that obtained
with on-surface emitters.
The localized and limited wetting pattern by drip systems requires the application of
fertilizers through the drip system, a technique named fertigation.
The great number of water emitters per unit area requires the minimization of the
single emitter’s flow-rate (discharge). The customary dripper flow-rate range is 0.1 –
8 liter per hour (l/h). The low emitter flow-rate is achieved by diverse designs: a tiny
orifice, large head losses within a long flow path, turbulent or vortex flow.
The narrow passageways in the emitters and the low flow rates lead to the
accumulation and precipitation of substances that may fully or partially clog the
system. Adequate filtration is a prerequisite for the implementation of drip irrigation.
Complementary chemical treatments are required when low quality water is used for
irrigation.
ADVANTAGES AND LIMITATIONS OF DRIP IRRIGATION
Advantages
Drip irrigation technology has many advantages over other irrigation technologies.
Drip irrigation significantly increases the efficiency of water utilization and improves
the growing conditions of the irrigated crops.
• Accurate localized water application: Water is applied precisely to a
restricted soil volume, corresponding with the distribution of the root system.
Appropriate water management can minimize water and nutrient losses
beneath the root-zone.
• Minimization of evaporation losses: The reduced wetted upper surface area
decreases water losses by direct evaporation from soil surface.
• Elimination of water losses at the plot's margins: with drip irrigation, water
does not flow beyond the limits of the irrigated plot as happens with sprinkler
irrigation. The drip system can actually fit any plot, regardless of shape, size or
topography.
• Decrease in weed infestation: The limited wetted area decreases the
germination and development of weeds.

17. DRIP IRRIGATION
6
• Desirable air-water equilibrium: The soil volume wetted by drip irrigation
usually retains more air than a soil that is irrigated by sprinkler or flood
irrigation.
• Simultaneous application of water and nutrients: Application of nutrients
together with the irrigation water directly to the wetted soil volume, decreases
nutrient losses, improves nutrient availability and saves the labor and/or
machinery required for the application of fertilizers.
• Adjustment of water and nutrient supply to changing crop demand along
the growing season: Fertigation technology together with high frequency
water and nutrient applications facilitate the tuning of the supply to the
dynamic requirements of the crop.
• Automation: Automatic controllers can easily be incorporated in drip irrigation
systems.
• Adaptability to harsh topographical and soil conditions: Drip irrigation
functions successfully on steep slopes, shallow and compacted soils with low
water infiltration rate and sandy soils with low water-holding capacity.
• Irrigation does not interfere with other farming activities: The partial
wetting of the soil surface does not interfere with other activities in the plot,
such as spraying, fruit thinning and harvesting.
• Water distribution is not disturbed by wind: Drip irrigation can proceed
under windy conditions. Wind does not interfere with drip irrigation, unlike in
sprinkler irrigation.
• Low energy requirements: Due to the low working pressure, energy
consumption in drip irrigation is significantly lower than that of other
pressurized irrigation technologies such as sprinkler and mechanized irrigation
systems.
• Decrease in fungal leaf and fruit diseases: Drip irrigation does not wet the
plant's canopy. This reduces the incidence of leaf and fruit fungal diseases.
• Avoiding leaf burns: The elimination of foliage wetting reduces leaf burns by
salt and fertilizers present in the irrigation water.
• Allows for extended use of brackish water for irrigation: Frequent
watering with drip irrigation allows for the use of irrigation waters containing a
relatively high concentration of salt with minor impact on plant development
and yield. The frequent applications dilute the salt concentration in the soil
solution beneath the emitter and drive the salt to the margins of the wetted soil
volume.
Limitations
Due to the limited wetted soil volume, the narrow water passageways in the emitters
and the vast amount of equipment needed, drip irrigation has some drawbacks.
• Clogging hazard: The narrow passageways in the emitters are susceptible to
clogging by solid particles, suspended organic matter and chemical
precipitates formed in the water. Clogging may also occur by suction of soil
particles and root intrusion into the dripper.

18. DRIP IRRIGATION
7
• High initial cost: Due to the large amount of laterals and emitters, mobility of
drip systems during the cropping season is rarely feasible. Most systems are
solid-set arrays, resulting in high cost of equipment per area unit.
• Salt accumulation on the soil's surface: Upward capillary movement of
water from the wetted soil volume and evaporation from the soil's-surface
leave behind a high concentration of salts in the upper soil layer. Light rains in
the beginning of the rainy season, leach the accumulated salts into the active
root zone and may cause salinity damage to the crop.
• Vulnerability of on-surface laterals and drippers to damage by animals:
The laterals, particularly the thin-walled tapes and the tiny drippers are prone
to damage by rodents, rats, moles, wild pigs and woodpeckers. Subsurface
laterals and drippers may be also damaged by rodents.
• Negligible influence on microclimate: Irrigation is occasionally used to
improve local climate conditions – reducing temperature during heat spells
and rising the temperature during frost events. With sprinkler and sprayer
irrigation, a fraction of the sprinkled water evaporates, releasing energy to the
atmosphere in cold weather and absorbing heat in hot weather. Naturally, this
does not occur with drip irrigation
• Restricted root volume: The frequent water applications to limited soil
volume lead to the development of restricted and sometimes shallow root
systems. As a consequence, the crop depends on frequent water applications
and increases its susceptibility to water stress during extremely hot weather.
High-velocity winds can uproot large trees with shallow root systems.

19. DRIP IRRIGATION
8
Chapter 3. THE DISTRIBUTION OF WATER IN THE SOIL
The flow of water and its distribution within the soil by drip irrigation is different from
that obtained with other irrigation techniques. Water is applied from a point or line
source. Point sources are discrete drippers which each of them wets a discrete
volume of soil. Line sources are drip laterals in which the drippers are installed close
to each other. The water flows along the lateral so that the wetted volumes formed by
adjacent emitters, overlap and create a wetted strip. With on-surface drip irrigation,
the wetted soil surface area is a small fraction of the total soil surface area. A small
pond is created beneath each emitter. The pond's dimensions depend on the soil
type and the emitter's flow rate. In light sandy soil, the pond is tiny and is actually
hardly observed. In soils of heavier texture, the pond's diameter is greater. Water
distribution within the soil follows a three-dimensional flow pattern, compared with the
one-dimensional, vertical percolation pattern typical of flood and sprinkler irrigation
that wet the entire soil surface area. With subsurface drip irrigation, the wetting
pattern is quite different. Water moves downward, sideways and also upwards.
Fig. 4. Water distribution in the soil along time: (a) on-surface drip irrigation. (b) SDI
Two driving forces simultaneously affect the flow of water in the soil: gravity and
capillary force. Gravity drives the water downwards. Capillary forces drive the water
in all directions. The equilibrium between these two forces determines the distribution
pattern of water within the soil.
The water distribution pattern affects the spreading of the roots in the soil and also
the distribution and accumulation of the dissolved chemicals - nutrients and salts.
Soil Wetting Patterns
The main factors affecting the distribution pattern of water and solutes in the wetted
soil volume with drip irrigation are listed below:

20. DRIP IRRIGATION
9
Soil Properties
Capillary forces are more pronounced in finer textured soils than gravity; hence the
horizontal width of the wetted soil volume is greater than the vertical depth. The
wetted volume shape resembles the shape of an onion. In medium textured soils, the
wetted volume is pear-shaped, and in soils with a coarse texture the vertical water
movement is more pronounced than the horizontal one so that the wetting volume
resembles a carrot.
Soil structure also influences water distribution. Compact layers and horizontal
stratification enhance the horizontal flow of water at the expense of vertical
percolation. On the other hand, vertical cracking in compacted soils enhances
preferential downward flow of water followed by incomplete wetting of the upper soil
layers.
Lateral Placement
The greatest wetting horizontal diameter by drippers of on-surface drip laterals
is near the soil surface, 10 – 30 cm deep.
The greatest wetting horizontal diameter by drippers of subsurface drip laterals
is at the depth of the lateral.
The vertical dimension of wetted soil above the emitter in SDI is about ¼ of the
wetted width in sandy soil and about ½ of the wetted width in silty and clayey soils.
Emitter Flow Rate
For the same application
time-length and amount
of water applied:
• A lower flow rate
renders a narrow
and deeper
wetting pattern.
• A higher flow rate
renders a wider
and shallower
wetting pattern.
• On-surface
drippers create
wider on-surface
ponds and the
horizontal wetted
diameter is bigger
than in lower flow
rates.
Emitter Spacing
For the same application
time-length and volume of water applied:
Narrow spacing with overlapping renders narrower and deeper wetting pattern. The
wetted width by each dripper increases until adjacent circles overlap. After
overlapping, most of the flow is directed downwards
Fig. 5. Water distribution from a single dripper in loamy
and sandy soil. 4 l/h and 16 l/h flow rates, 4, 8, 16 l dose
After Bressler 1977

21. DRIP IRRIGATION
10
Wide spacing renders wider and shallower wetting pattern.
Water Dosage
The wetted volume grows wider and deeper as the applied water amount increases.
Chemical Composition of the Water
Chemical compounds dissolved in the water may change the wetting pattern.
Detergents and other surfactants contained in reclaimed and storm waters reduce
water's surface tension and decrease the horizontal flow.
The lower surface tension increases the affect of gravity at the expense of the
capillary forces, resulting in a narrower and deeper wetting pattern.
Salt and Nutrient Distribution
Dissolved salts tend to accumulate at the perimeter of the wetted zone, particularly at
the soil surface where the water content of the soil is lower. A saline ring develops
around the wetted circles on the soil's surface, along with a zone of salt accumulation
at a depth which depends on the leaching efficiency. Good drip irrigation
management at an appropriate irrigation frequency, replenishes the water removed
by the crop, so that the soil water content in the soil remains high enough to maintain
a low concentration of soluble salts. The nutrients applied with the irrigation water
also follow the same distribution pattern.
Fig. 6. Salt distribution in the wetted volume
Adapted from Kremmer & Kenig, 1996
Fig. 7. Leaching of salt into the active root-
zone by rain Adapted from Kremmer & Kenig, 1996
Salt accumulation at the soil's surface and in the uppermost soil layer requires
implementation of preventive measures with the first rains after a dry season.
Irrigation should be applied as long as the rain lasts as to avoid the accumulation of
the salts leached from the soil surface into the active root-zone.
Soil Properties that affect the Water Distribution Pattern
As mentioned before, soil properties affect the flow of water in the soil as well as the
pattern of the wetted volume.

22. DRIP IRRIGATION
11
The balance between the vertical and the horizontal movement is determined by soil
properties such as infiltration and percolation rates that are dependent on the soil’s
hydraulic conductivity. Hydraulic conductivity is expressed in units of velocity
(length/time) per unit cross section (m/sec). A given soil does not have a constant
value of hydraulic conductivity. In one and the same soil the hydraulic conductivity is
higher in saturated soil than in unsaturated state. It also depends on the degree of
stratification - the presence of compact soil layers and the moisture content of the soil
before irrigation. Though different mathematical models have been developed for the
prediction of soil water distribution patterns, the use of empirical field techniques for
the estimation of the size and volume of the wetted soil is preferable.
While plants are not consuming water, as it happens at night, the volume of the soil
that is wetted depends on the volume of water applied by the dripper and the change
in water content in the wetted volume.
V = L X [100/(Mf-Mi)]
Where
V = Soil wetted volume, l'.
L = Amount of the applied water, l'
Mf is the average percentage of water content per unit volume in the wetted zone
after irrigation and Mi is the average percentage of soil water content per volume unit
before irrigation.
For example, if 100 l' of water were applied at night and the soil water content in the
wetted volume increased by 10% per volume, then the wetted volume would be 1000
l' (1 m3
) of soil.
Mf – Mi = 10%
V = 100l X (100/10) = 1000l
Wetting Width and Depth
Selection of the most suitable dripper and determination of the spacing between
laterals and between drippers on the lateral, commit a thorough estimation of the
wetting pattern of the soil by the drippers.
For a simple estimation of the width and depth of soil wetting, it is assumed that the
capillary forces drive the flow of water in the soil at the same rate in all directions and
gravity drives the water downward. For a given amount of applied water, the balance
between these two forces determines the dimensions of the soil wetted volume and
the ratio between the vertical and horizontal axis. During the wetting of a dry soil,
gravity initially drives the water downwards through the empty, non-capillary voids
much faster than the horizontally capillary movement. As the capillary voids are filled
with water, the horizontal flow becomes more pronounced. This happens earlier at
higher flow rates, therefore the horizontal diameter of the wetted volume by drippers
with higher flow rates is larger. The same happens with soils of fine texture. Vertical
gravity-driven percolation is slower and the capillary voids are filled earlier with water.

23. DRIP IRRIGATION
12
Schwarzman and Zur developed a semi-empirical formula for estimation of the
dimensions of the wetted volume:
W = K3 (Z)0.35
(q)0.33
(Ks)-0.33
When: W = Max width of the wetted volume (not of the wetted area on soil surface)
K3 = 0.0094 (empirical coefficient)
Z = Desired depth of the wetting front – m (related to depth of the active root system).
q = Dripper flow rate l/h
Ks = Saturated hydraulic conductivity – m/s (has to be measured in laboratory or
taken from a table)
The result of using this formula differs in many cases from the empirical
measurements in the field, since the hydraulic conductivity is determined in the
laboratory on a disturbed soil sample. Whenever possible, it is recommended to
determine the wetting pattern in undisturbed soil in the field.
The distribution of nutrients applied by fertigation depends significantly on the
interaction between the nutrient ions and the soil.
Potassium ions are absorbed on the surface of clay minerals so that their transport
with irrigation water in fine and medium textured soils is limited and most of the
applied potassium remains in the upper soil layers.
Phosphorous precipitates from the soil solution as insoluble salts with calcium and
magnesium in basic and neutral pH levels and with iron and aluminum in acid soils.
In these cases, it remains in the upper soil layer. In SDI, application of phosphorous
in deeper soil layers increases its availability and absorption by the root system.
Root System Development under Drip Irrigation
It is well known that the water application regime and water distribution pattern in the
soil affect the pattern of root system development.
Each plant family has a typical root distribution pattern, stemming from the growing
conditions in the plant’s site of origin and its adaptation of the plant to the local
growing environment.
Fig. 8. Diverse root systems
As depicted in the above drawing, root systems can be shallow or deep, dense,
branched or sparse, mostly unrelated to the shape of the plant's canopy.

24. DRIP IRRIGATION
13
The root system pattern and soil properties are important factors in determining
dripper spacing and the scheduling of the irrigation regime. Shallow and sparse root
systems require a close dripper spacing and frequent water applications, while deep
and branched root systems allow for wider spacing and larger intervals between
irrigations.
Frequent and small water applications
by drip irrigation lead to the
development of shallow and compact
root systems. This increases crop
sensitivity to heat spells and water
stress. Large plants with shallow root
systems are prone to uprooting by
strong storms.
On the other hand, because of the
improved aeration and nutrition in the
drip irrigated soil volume, the density of
the active fine roots is significantly
higher than the density of root systems that grow under sprinkler irrigation.
grow under sprinkler irrigation.
Fig. 10. Root system in drip irrigation (left) vs. root system in sprinkler irrigation (right) Courtesy “Netafim”
The active root system and most root-hairs of drip-irrigated orchard trees, are
concentrated in the wetted volume. The highest density of the active roots is in the
aerated upper layers, provided there is no accumulation of salts. At the margins of
the wetted volume, where salt accumulates, active roots are sparse.
Evergreen fruit trees such as avocado and citrus develop shallower root systems
under drip irrigation than deciduous orchards and vineyards. This determines the
irrigation regime and necessitates the addition of a second drip lateral per row on
light textured soil.
With SDI, the root distribution pattern is different. Roots are mainly concentrated
under and beside the laterals. Very few roots develop above the laterals due to the
higher salinity in these soil layers.
Fig. 9 Typical root systems of field crops

25. DRIP IRRIGATION
14
Chapter 4. THE DRIP SYSTEM
Although the drippers are the core of the drip irrigation network, the system is made
up of many additional components. These components have to be compatible with
each other, with the crop demands and with the characteristics of the plot to be
irrigated.
The components are classified in six principal categories:
• Water source: A pumping system from an on-surface or underground source
or a connection to a public, commercial or cooperative supply network
• Delivery system: Mainline, sub-mains and manifolds (feeder pipes)
• Drip laterals
• Control accessories: Valves, water meters (flow-meters), pressure and flow
regulators, automation devices, backflow preventers, vacuum and air release
valves, etc.
• Filtration system
• Equipment for the injection of plant nutrients and water treatment agents
The Water Pumping/Supply Head
There are two alternative sources of
water supply:
a. independent pumping from an on-
surface source (such as a lake, river,
stream, pond or dam reservoir) or from
an underground source (such as a well).
b. connection to a commercial, public or
cooperative supply network on the other.
With independent pumping, the pump is
chosen according to the discharge and
pressure requirements in the irrigated
area.
In connection to a water supply network,
the diameter of the connection, main
valve and the delivering pipeline should
correspond with the planned flow-rate and the requested operating pressure, with the
smallest possible friction head losses.
The Delivery System
Mainlines for water delivery and distribution
Pipes are made of PVC or polyethylene (PE). PVC pipes are installed underground
as usually they have no protection against UV-radiation. PE pipes are installed
underground or above ground, as they contain carbon black, which provides UV
protection. The pipes’ PN (nominal working pressure) has to be higher than the PN of
the drip laterals, particularly if the system has to withstand pressure with closed
valves. The most common PN of delivery and distribution lines is 6 – 8 bar (60 – 80
m pressure head).
Fig. 11. Simplified scheme of drip system

26. DRIP IRRIGATION
15
Sub-mains
The sub-mains are installed under or above ground. Underground installed pipes can
be made of PVC or PE, while above-ground installed pipes can only be made of PE.
In the case of retrieveable drip systems for the irrigation of annual crops (the system
is layed out at the beginning and retrieved at the end of the growing season). Above-
ground pipes can be made of P.E., aluminum or vinyl “lay-flat” hose. The lay-flat hose
is durable and lays flat when not in use, so mechanic equipment can travel over it.
The lay-flat hose, connectors, and feeder tubes are retrieved after the growing
season to be used for the irrigation of another plot or stored until the following
season. Wide-diameter PE pipes are more rigid, and are not easily rolled up at the
end of the season.
Manifolds
In certain circumstances, when rows are very long or in harsh topographic conditions,
sub-division of the plot by sub-mains is insufficient. In these conditions, additional
division is accomplished by manifolds.
Fig. 12. Typical layout of drip irrigation system
Drip Laterals
The drip laterals are connected to the sub-mains or the manifolds. The laterals are
made of LDPE (Low Density Polyethylene). There are different types of connectors
between the sub-mains/manifolds and the laterals. The connectors have to withstand
the working pressure as well as pressure spikes and water hammers. The lateral may
be laid on soil surface or underground (SDI). Shallow burying, 5 – 10 cm below soil
surface is common in vegetables grown under plastic mulch.
Two basic types of drip laterals are used: Thick-walled laterals with on-line or in-line
discrete drippers and thin-walled tapes with turbulent flow inherent water
passageway molded into the tape during the extrusion process. The tape shrinks

27. DRIP IRRIGATION
16
when it is not under water pressure. Thick-walled laterals have a PN of 1 – 2 bar (10
– 20 m), and tapes have a PN range from 0.4 to 1 bar (4 – 10 m).
Control and Monitoring Accessories
Valves and Gauges
Simultaneous irrigation of several plots, each one with different water requirements
from a single water source requires the sub-division of the irrigated area into sectors,
each controlled by its assigned valve. These valves can be operated manually or
automatically. Water-meters as well as automatic water-metering valves are used to
measure and control water supply to the various sectors.
Pressure regulators are used to prevent excessive pressure above the working
pressure of the system.
A backflow prevention/anti-siphon valve is required if the water is supplied from a
well or a municipal water source that distribute drinking water, when fertilizers or
other chemicals are injected into the irrigation system.
Air-release/relief valves have to be installed at the highest topographic points of the
system in order to avoid interference with water flow, excessive friction with pipe
walls and pipe burst as an outcome of the flow of a high volume of air in the system.
Vacuum breakers are used to avoid the collapse of pipes in steep slopes. In SDI
systems, they are installed to avoid suction of soil particles into the drippers after
shut-down of the water supply.
Fig. 13. Components of drip irrigation system
Filtration
The narrow passageways of the emitters are susceptible to clogging by suspended
matter and chemical precipitates from the irrigation water. Three measures are taken
to prevent clogging:
• Preliminary separation of suspended solid particles by settling ponds, settling
tanks and sand separators.

28. DRIP IRRIGATION
17
• Filtration of the irrigation water.
• Chemical treatments for decomposition of suspended organic matter, blocking
the development of slime by microorganisms and prevention of precipitates
deposition.
Filtration devices are usually installed at the control head. When the irrigation water
is heavily contaminated, a main filtration system is installed at the plot control head
and secondary control filters are installed at the sectorial control heads. Filters should
be flushed and cleaned routinely. Flushing can be manual or automatic. Automatic
back-flushing of media filters is performed with filtered water, hence, the filters are
installed in pairs and flush one-another alternately.
Chemical Injectors
Three types of chemicals are injected into drip irrigation systems: fertilizers,
pesticides, and anti-clogging agents. Fertilizers are the most commonly injected
substances; the ability to “spoon-feed” nutrients contributes to the increased yields
obtained with drip irrigation.
Systemic pesticides are injected into drip irrigation systems to control insects and
protect plants from certain diseases.
Chemicals that clean drippers or prevent dripper clogging are also injected.
Chlorine is used to kill algae and microorganisms and for decomposition of organic
matter, while acids are used to modify water pH and dissolve precipitates.
The different types of injectors are described in the chapter on fertigation.
Fig. 14. Control Head Courtesy “Netafim”

29. DRIP IRRIGATION
18
Chapter 5. FLOW RATE - PRESSURE RELATIONSHIP
Water Pressure
Water pressure is a key factor in the performance of pressurized irrigation systems.
Pressure can be expressed in different unit systems.
Table 1. Pressure units
Definition Unit Sub units Conversion
Pressure/Tension Bar =100 Centibar 0.99 Atm.
Pressure/Tension Kilopascal (kPa) = 1000 Pascal 0.01 Bar=1 Centibar
Pressure/Tension Atmosphere (Atm) ~100 Centibar 1.01 Bar
Head Meter =100 cm 0.1 Atm. ~ 0.1 Bar
For simplicity and convenience in the design of irrigation systems, the preferred unit
system is pressure head, expressed in meters (m) height of water column. Pressure
is converted to head units by dividing the pressure (weight/area) by the water’s
specific weight (weight/volume). Therefore the head units are length (m) units.
For example: A pressure of 5 atmospheres (5 kg/cm2
) divided by water’s specific
weight (1 g/cm3
) equals (5000 g/cm2
)/(1 g/cm3
) = 5000 cm = 50 m. In practice, a
column of water with cross section of 1 cm2
and weighing 1 Kg is 10 m high.
This unit system enables the concurrent calculation of the effects of topography and
friction losses due to the flow of water in the pipes on the pressure head at each
point of the irrigation system. Water pressure head can be referred to as the water’s
hydraulic potential energy. This potential energy is capable to accomplish work, e.g.
to move a certain mass of water along a certain distance.
Water Head Components
The total water head, measured at a specific point of the irrigation system, is made-
up of three components:
Elevation Head (z)
Elevation head is due to the topographical position, the relative height of a given
point above or below a fixed point of reference. For example, if the main valve in the
plot lies 5 m above the distal end of the plot, the measured static (elevation) head at
the distal end will be 5 m higher than the measured static head at the valve. Static
head is the pressure measured in a point in the water system when no water flow is
taking place.
Pressure Head
Water under high pressure has more energy than water under low pressure.
Although water is considered incompressible, water under pressure is stressed by
the pressure. The resultant stress compresses the water and squeezes the bonds
and electric fields in and around the water molecules. The water absorbs the energy
that pushes the water molecules back against the surrounding water molecules and
the container wall. The energy stored in the water molecules and the bonds between
them is available to move the water to lower energy points.

30. DRIP IRRIGATION
19
Velocity Head
Flowing water has kinetic energy (velocity energy) represented by V2
/2g where V is
velocity which is measured in m/sec and g is the gravitational constant 9.81 m/sec2
.
Squaring V by itself (V x V = V2
) results in units of m2
/sec2
which divided by g in m
/sec2
gives velocity head in m. units.
Conservation of Hydraulic Energy
Globally, energy is never perished, it only changes forms. Hydraulic energy may
change back and forth between the three forms; elevation energy, pressure energy
and velocity energy. Some of it may be lost from the system and dissipated as heat
due to friction, but it is still all there. If the sum of the three energy components does
not remain constant as water flows through the irrigation system, then energy must
either be added by a pump or booster, or be lost by friction. Between any two points,
point 1 and point 2, in a closed system, changes in energy are accounted with the
following formula:
P1 + V12/2g + Z1 + Energy Added (pump head) = P2 + V22/2g + Z2 + Head Losses
Initial Hydraulic Energy Final Hydraulic Energy
Pressure Head @1 + Velocity Head @1 + Elevation Head @1 + Pump Head Added
Equals
Pressure Head @2 + Velocity Head @2 + Elevation Head @ 2 + Friction Losses
The above expression is known as Bernoulli’s Equation which is used to solve
hydraulic problems in irrigation systems.
The two dynamic components in this expression are the pump’s energy (added) and
the friction losses (subtracted).
Head losses are the consequence of friction between the pipe's walls and water as it
flows through the system and meets obstacles (turns, bends, expansions and
contractions) along its way.
The degree of head loss is a function of the following variables:
a. Pipe length
b. Pipe diameter
c. Pipe wall smoothness
d. Water flow-rate (discharge)
e. Water viscosity
Diverse theoretical and empirical equations have been developed to calculate these
losses.
Friction Losses
There are two types of friction losses: friction losses in water flow along straight
pipes, defined as major losses; and friction losses due to the turbulent flow at bends
and transitions, defined as minor (local) losses. If the flow velocities are high and
there are many bends and transitions in the system, minor losses can build-up and
be quite considerable. The most common equation used to compute friction losses
of water flow along a pipe is known as the Hazen-Williams formula.
J = 1.135 x 1012
(Q/C)1.852
X D-4.871

31. DRIP IRRIGATION
20
Where:
J = head loss (‰ =m/1000 m)
D = inner pipe diameter (mm)
C = friction coefficient (indicates pipe wall smoothness, the higher the C
coefficient, the lower the friction head loss)
Q = flow-rate (m3
/h)
Minor (local) Head Losses
Minor head losses are usually
defined as equivalent length
factors which add a virtual
length of straight pipe in the
accessory same diameter to
the length of the pipe under
calculation.
Total Dynamic Head
The total dynamic head
created by the pump is the
sum of the pumping suction lift (the difference between water surface height at the
source and pump height), the requested working pressure in the emitters, and friction
losses within the irrigation system.
The energy consumed per pumped unit of irrigation water depends on the total
dynamic head provided by the pump and the pumping system's efficiency. The total
dynamic head depends on:
• Vertical distance that the water is lifted
• Pressure required in drippers' inlets
• Friction losses in the pipeline along the way from the water source through filters,
valves, pipelines and manifolds on the way to the emitters
Pumping system efficiency depends upon the pump efficiency, its power unit
efficiency, and the efficiency of power transmission of power between them.
The power output required by the pump is calculated with the formula below:
Q x H
N = ----------
270 x ŋ
Where: N = required input – HP
Q = pump discharge – m3
/h
H = total dynamic head – m
η = pump efficiency – decimal fraction
Example: Q = 200m3
;
H = 150 m;
ηηηη = 0.75.
N = 200 X 150/(270 X 0.75) = 148 HP
When measuring pressure, it should be remembered that the pressure gauges are
calibrated to read 0 (zero) at atmospheric pressure (about 1 bar). It is important to
Table 2. The friction coefficient ( C ) of pipes
Pipe material
C
PVC and PE 140-150
Asbestos-cement 130-140
New steel 110-120
5 year old steel 80-90
Steel with internal concrete coating 110-120
Concrete 90-100

32. DRIP IRRIGATION
21
remember this fact for the operation of devices such as Venturi suction injectors in
drip irrigation.
Absolute Pressure
Absolute pressure is the formal expression of total force per unit area. It is composed
of the pressure of the atmosphere, the pressure due to any external forces applied
on the fluid and the pressure resulting from the weight of the fluid itself.
Gauge Pressure
The gauge pressure is the absolute pressure minus the atmospheric pressure that
typically acts in all directions and on all objects in open air. Since atmospheric
pressure at sea level height is typically about 1 bar, an absolute pressure of 3 bars
would be equivalent to a gauge pressure of 2 bar (~20 m pressure head).
Working Pressure
The working pressure is the pressure required at the emitters to guarantee effective
performance and uniform water distribution. The range of the appropriate working
pressure of the emitter is defined and published by the manufacturer in the operating
guide. The type of the emitter chosen and its working pressure, have to be taken into
account in the design of the irrigation system and in the irrigation scheduling. The
distributing pipelines are designed to deliver the water to the emitters with such
pressure losses that guarantee the appropriate working pressure in the emitters, so
that water will be applied uniformly in the whole irrigated block.
Although there are a number of formulae for calculation of head losses, in daily life,
tables, nomograms and dedicated software are mostly used.
When calculating the head losses in a pipe network, a distinction is made between
the flow in pipes with a single outlet at their distal end and distributing pipes with
multiple outlets. In a non-distributing pipe, head loss values taken from a table or a
nomogram are expressed in % or ‰ units by its length in m. Multiplication by the pipe
length in m. length units renders the actual losses in m. head units.
Christiansen friction factor (F) is used also to calculate the head losses in pipes with
multiple outlets such as drip laterals, This factor accounts for the decrease in flow
along the lateral and depends upon the number of outlets or emitters (N) and the
exponent (m = 1.852) of (Q) in Hazen-Williams equation. The formula to calculate
this factor is as follows
F = 1/(m+1) + 1/(2N) +((m-1)0.5
/(6N)2
)
For a lateral with more than 10 emitters, F= 0.35 can be used regardless of which
friction loss calculation formula is used. The head loss due to friction in drip laterals is
then determined by Hl = F(Hlp), where Hl is the head loss due to friction in the drip
lateral and Hlp is the head loss due to friction of the same discharge in a pipe of the
same diameter and length but with a single outlet at the end. As mentioned above, Hl
= 0.35 Hlp can be used when there are more than 10 outlets on the pipe.
Hydraulic Characteristics of the Emitter
The flow-rate of emitters in micro-irrigation is affected variably by pressure
fluctuations. The performance of a given model depends on its design and
construction. The relationship between the emitter operating pressure and flow-rate
is calculated with the following equation:

33. DRIP IRRIGATION
22
Q = kPe
Where: Q = dripper flow-rate – l/h
k = dripper constant – depends on the units of flow rate and pressure head.
P = Pressure at the dripper's inlet – m
e = dripper discharge exponent (dripper exponent)
The dripper exponent indicates the specific relationships between the working
pressure and the flow-rate of the emitter. The range of emitter exponents is 0 – 1.0
Drippers with laminar flow pattern have high exponents, in the range of 0.7 – 1.0.
Drippers with turbulent flow pattern have exponents between 0.4 and 0.6.
Compensating drippers have exponents which approach zero in the regulated flow
range.
The larger the dripper exponent, the more sensitive the flow-rate is to pressure
variations. A value of 1 means that for each percent change in pressure there is an
identical percent change in flow rate. On the other side, an exponent value of 0 (zero)
means that the emitter flow-rate does not change at all as pressure changes.
Table 3. The effect of dripper exponent on pressure – flow-rate relationships
% flow rate change% pressure
change
Exponent ----> 0.4 0.5 0.6 0.7 0.8
10 3.9 4.8 5.9 6.9 7.9
20 7.6 9.5 11.6 13.6 15.7
30 11.1 14.0 17.1 20.2 23.3
40 14.4 18.3 22.3 26.6 30.9
50 17.6 22.5 27.5 32.8 38.3
Fig. 15. Relationship between the dripper exponent and lateral length Courtesy “Netafim”

34. DRIP IRRIGATION
23
Whenever the laterals are laid out on the soil surface, the ambient temperature
affects dripper flow-rate. As water temperature increases, water viscosity decreases
and the discharge increases. Lateral heating is more pronounced at the distal end
due to decrease in flow velocity. As a result, the emitters in the lateral's end may
have a higher flow-rate than the emitters at the beginning of the laterals.
In pressure compensating
(PC) drippers, pressure
fluctuations above the
threshold of the regulating
pressure do not affect the
flow-rate. The regulating
pressure is that head
range in which regulation
of flow-rate takes place.
The graphs to the right
show that in Ram PC
drippers, the regulating
pressure threshold is
about 4 m.
Calculation of the Head
Losses
As mentioned before, slide
rulers, tables, nomograms,
hand-held and on-line
calculators as well as
dedicated software can be
used for the calculation of
head losses. Pipe and
accessories manufacturers publish tables and nomograms depicting the head losses
in their products. Valve producers use the Kv coefficient that designates the
discharge of the valve in m3
/h at which 10 m head (1 bar) are lost by friction.
Table 4. Head losses in Acuanet automatic valve
ModelFlow m3/h
1" El/St 1½" El/An 1½" El/St 1½" Hy/St 2" El/St 2" Hy/An 2" Hy/St 2" Hy/An
3 1.6 0.5 0.4 0.3 0.3 0.2 0.3 0.2
5 2.3 0.5 0.4 0.3 0.6 0.4 0.3 0.3
7 4.7 1.3 1.0 0.7 0.9 0.7 0.5 0.8
10 2.2 1.8 1.3 1.5 1.0 1.0 1.0
12 3.0 2.2 1.3 1.9 1.3 1.4 1.2
14 3.5 2.8 2.2 2.4 1.7 3.4 1.4
16 4.6 3.4 3.0 3.0 1.9 2.4 1.6
18 5.8 4.3 4.0 3.6 2.4 3.2 2.1
20 6.6 5.2 4.7 4.2 2.9 3.8 2.6
24 8.5 6.5 6.5 5.6 3.8 5.5 3.6
28 7.2 4.9 7.2 4.6
32 9.6 8.8 8.5 6.4
El=Electric; An=Angular; St=Straight;Hy=Hydraulic Courtesy "Netafim"
Fig. 16. Pressure Compensated dripper flow-pressure relationship
Fig. 17. Non-pressure compensated flow-pressure relationship

35. DRIP IRRIGATION
24
Technical Data
Dripper manufacturers provide detailed technical
data, in catalogues or on-line, about the flow-rate -
pressure relations of their products, such as the
dripper's coefficient and the dripper exponent. This
information should be utilized for the design of
lateral length and the pressure required at the
lateral's inlet. Low dripper exponents allow higher
pressure difference between drippers without
deviating from the rule allowing flow-rate difference
of 10%. (This rule is dealt with in the topic on
system design).
Adapted from "Plastro" CD-Rom
This example shows that a large difference in pressure head – up to 20%, is
tolerated for drippers with a dripper exponent of 0.5 and below.
A comprehensive nomogram for the estimation of friction losses in straight pipe
sections that can be used with any type of pipe is presented overleaf. The example
shows the head loss (in J ‰) for a flow-rate of 200 m3
/h through a pipe with an inner
diameter of 200 mm.
The first step is to draw a straight line from Q=200 on the left scale through the 200
mm point on the D mm scale. The crossing point of the ruler with the axis (the blank
line) has to be clearly marked.
The second step is to draw a straight line connecting the mark through the relevant
friction coefficient on the scale C and to mark the point where this line crosses the
scale J0
/00. The value of the crossing point is the head loss in 0
/00 (m pressure head
per 1000 m length of the pipe.
The following nomograms are useful for LDPE and HDPE pipes. In each nomogram,
the relevant PN values are designated under "Class".
Fig. 18. Acuanet automatic valve
Table 5. "Plastro" Hydrodrip II integral drip laterals technical data
DIAMETER
mm
DRIPPER CONSTANTS DH=7.5% DH=10%EMITTER
TYPE
FLOW
RATE
l/h
NOMINAL
INTERNAL COEFFICIENT EXPONENT Pmin-m Pmax-m Pmin-m Pmax-m
12-/26/40 2.1 12 10.4 0.6442 0.506 9.25 10.75 9 11
16/18 1.6 16 15.2 0.5300 0.4830 9.19 10.81 8.91 11.09
2.2 16 15.2 0.7260 0.4840 9.19 10.81 8.91 11.09
3.6 16 15.2 1.1940 0.4792 9.19 10.81 8.90 11.10
16-/25/35 1.7 16 15.2 0.5212 0.5090 9.24 10.76 8.97 11.03
-40/45 2.3 16 15.2 0.7646 0.4704 9.17 10.83 8.88 11.12
3.6 16 15.2 1.1940 0.4792 9.19 10.81 8.90 11.10
20-/24/36/44 1.7 20 17.6 0.5212 0.5090 9.24 10.76 8.97 11.03
2.3 20 17.6 0.7646 0.4704 9.17 10.83 8.88 11.12
3.6 20 17.6 1.1940 0.4792 9.19 10.81 8.90 11.10
25-/17/34 1.7 25 22.2 0.5212 0.5090 9.24 10.76 8.97 11.03
2.3 25 22.2 0.7646 0.4704 9.17 10.83 8.88 11.12
3.6 25 22.2 1.1940 0.4792 9.19 10.81 8.90 11.10

36. DRIP IRRIGATION
25
Fig. 19. Head loss nomogram, based on Hazen-Williams formula

37. DRIP IRRIGATION
26
Fig. 20 Nomogram for calculation of head losses in HDPE pipes Adapted from "Plassim" brochure

38. DRIP IRRIGATION
27
Fig. 21 Nomogram for calculation of head losses in LDPE pipes Adapted from "Plassim" brochure
The class designation relates to the working pressure (PN) in atm. 1atm = 10 m ≈ 1 bar

39. DRIP IRRIGATION
28
Chapter 6. PIPES AND TUBES FOR DRIP IRRIGATION
The commercial development of drip irrigation is based on the use of plastic
materials. Drippers, pipes and most of the other drip system components are made of
plastic materials.
Plastic solid materials are comprised of one or more polymeric substances that can
be shaped by molding or extrusion. Polymers, the basic ingredient of plastic
materials, are a broad class of materials that include natural and synthetic
substances. In professional terminology, polymers are frequently defined as resins.
For example, a polyethylene (PE) pipe compound consists of PE resin combined with
colorants, stabilizers, anti-oxidants and other ingredients required to protect and
enhance the quality of the material during the fabrication process and operation in the
field.
Plastic materials are divided into two basic groups: thermoplastics and thermosets,
both of which are used for the production of plastic pipes.
Thermoplastics include PE, polypropylene, polybutylene and PVC. These materials
can be re-melted by heat. The solid state of thermoplastic materials is the result of
physical forces that immobilize polymer chains and inhibit them from slipping past
each other. When heat is applied, these forces weaken and allow the material to
soften or melt. Upon cooling, the molecular chains stop slipping and are held firmly
against each other in the solid state. Thermoplastics can be shaped during the
molten phase of the resin and therefore can be extruded or molded into a variety of
shapes, such as pipes, flanges, valves, drippers and other accessories.
Thermoset plastic materials are similar to thermoplastics prior to a chemical reaction
(“curing”) by which the polymer chains are chemically bonded to each other by new
cross-links. That is usually performed during or right after shaping of the final product.
Cross-linking is the random bonding of molecules to each other to form a giant three-
dimensional association. Thermoset resins form a permanent insoluble and infusible
shape after applying heat or a curing agent. They cannot be re-melted after shaping
and curing. This is the main difference between thermosets and thermoplastics. As
heat is applied to a thermoset component, degradation occurs at a temperature lower
than the melting point. Thermosetting resins can be combined with reinforcements to
form strong composites. Fiberglass is the most popular reinforcement and fiberglass-
reinforced pipe (FRP) is a common form of thermoset-type pipes.
Polyethylene
Polyethylene (PE) is the most prevalent material in pipes and laterals in drip irrigation
systems. There are four types of PE, classified by material density:
Type I – Low Density (LDPE), 910 – 925 g/l
Type II – Medium Density (MDPE), 920 – 940 g/l
Type III – High Density (HDPE), 941 – 959 g/l
Type IIII – High Homo-polymer, 960 and above g/l
Carbon black 2% is added to reduce pipes’ sensitivity to ultraviolet (UV) sun
radiation.
PE pipes can be classified according to the working pressure (PN) they can
withstand. The common grades of PN used in irrigation are: 2.5, 4, 6, 10, 12.5 and 16

40. DRIP IRRIGATION
29
bars (atm). Some thin-wall laterals withstand much lower PN: 0.5 – 2 bar. The
tolerance to working pressure depends on pipe density and wall thickness. The
tolerance data given by the producers relates to temperature of 20 C0
. In higher
temperatures, the tolerance decreases significantly, hence pipes are tested at twice
their designated working pressure.
Plastic pipes are defined according to their external diameter, in mm. In the USA and
some other countries, pipe diameter is defined by imperial inch units (“). 1” = 25.4
mm. Pipe wall thickness is also defined in mm units (in the USA by mil units - 1/1000
of inch). 1 mil = 0.0254 mm.
Laterals are commonly made of LDPE (PE grade 32) while delivering and distributing
pipes with diameters greater than 32 mm are mostly made of HDPE.
HDPE pipes are further classified according the grade of the material: PE-63, PE-80,
PE-100. The higher the grade, the higher the pipe quality.
Table 6. PE (polyethylene) pipes for agriculture
PE type ND Applications PN - m
LDPE 6 mm Hydraulic command tubing 40 – 120
LDPE 6 – 10 mm Micro-emitters connection to laterals 40 – 60
LDPE 12 – 25 mm Thin-wall drip laterals 5 – 20
LDPE 12 – 25 mm Thick-wall drip laterals 25 – 40
LDPE 16 – 32 mm Micro and mini emitter laterals 40 – 60
HDPE 32 – 75 mm Sprinkler laterals 40 – 60
HDPE 40 – 140 mm Main lines and sub-mains 40 – 100
HDPE 75 – 450 mm Water supply networks 60 - 160
Table 7. Internal diameter and wall thickness of LDPE pipes
OD/PN 25 m 40 m 60 m 80 m 100 m
mm ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
12 9.8 1.1 9.6 1.2 9.2 1.4 8.6 1.7 8.0 2.0
16 13.2 1.4 12.8 1.6 12.4 1.8 11.6 2.2 10.6 2.7
20 17.0 1.5 16.6 1.7 15.4 2.3 14.4 2.8 13.2 3.4
25 21.8 1.6 21.2 1.9 19.4 2.8 18.0 3.5 16.6 4.2
32 28.8 1.6 27.2 2.4 24.8 3.6 23.2 4.4 21.2 5.4
40 36.2 1.9 34.0 3.0 31.0 4.5 29.0 5.5 26.6 6.7
50 45.2 2.4 42.6 3.7 38.8 5.6 36.2 6.9 33.4 8.3
Adapted form "Plastro" brochure
ND = Nominal Diameter
OD = External (Outer) Diameter. In plastic pipes it is mostly equivalent to the ND.
ID = internal (inner) Diameter

41. DRIP IRRIGATION
30
Table 8. Internal diameter and wall thickness of HDPE pipes
OD/PN 25 m 40 m 60 m 80 m 100 m 160 m
mm ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
12 8.6 1.7
16 12.8 1.6 11.6 2.2
20 16.8 1.6 16.2 1.9 15.4 2.8
25 21.8 1.6 21.1 1.9 20.4 2.3 18.0 3.5
32 28.8 1.6 28.2 1.9 27.2 2.4 26.2 2.9 23.2 4.4
40 36.8 1.6 35.2 2.4 34.0 3.0 32.6 3.7 29.0 5.5
50 46.8 1.6 46.0 2.0 44.0 3.0 42.6 3.7 40.8 4.6 36.2 6.9
63 59.8 1.6 58.2 2.4 55.4 3.7 53.6 4.7 51.4 5.8 45.8 8.6
75 71.2 1.9 69.2 2.9 66.0 4.7 64.0 5.5 61.4 6.8 54.4 10.3
90 85.6 2.2 83.0 3.5 79.2 5.5 76.8 6.6 73.6 8.2 65.4 12.3
110 104.6 2.7 101.6 4.2 96.8 6.6 93.8 8.1 90.0 10.0 79.8 15.1
125 118.8 3.1 115.4 4.8 110.2 8.1 106.6 9.2 102.2 11.4 90.8 17.1
140 133.0 3.5 129.2 5.4 123.4 9.2 119.4 10.3 114.6 12.7 101.6 19.2
160 152.0 4.0 147.6 6.2 141.0 10.3 136.4 11.8 130.8 14.6
180 172.2 4.4 166.2 6.9 158.6 11.8 153.4 13.3 147.2 16.4
Adapted form "Plastro" brochure
PVC Pipes
PVC (Polyvinyl Chloride) is a rigid polymer. To soften the material and enable its
shaping, it is common to add substantial amounts (up to 50%) of plasticizers. These
additives render flexibility to tubes made of soft PVC. PVC pipes are sensitive to UV
sun radiation. Soft flexible PVC pipes are used in a limited scale mainly in gardening
and landscape. Their life span is short. Rigid PVC pipes are used In agriculture
mainly for water delivery and distribution. PVC pipes are installed underground only,
to avoid UV radiation damage. In the last decade, UPVC (unplasticized PVC) pipes
are preferred because of their improved durability and ability to withstand pressure.
PVC pipes appear in discrete 4 – 8 m long segments and have to be jointed in the
field. The working pressure of rigid PVC pipes is 6 – 24 bars (60 – 240 m).
Table 9. PVC pipes for agriculture
PVC type ND Applications PN - m
Soft PVC 6 mm Hydraulic command tubing 40 – 80
Soft PVC 6 – 10 mm Micro-emitters connection to laterals 40 – 60
Soft PVC 12 – 25 mm Thin-wall drip laterals 5 – 20
Rigid UPVC ½” – 4” Risers 40 – 100
Rigid UPVC 63 – 1000
mm
Supply networks, main lines, sub-
mains
40 – 240
When PVC pipes are installed in heavy or stony soil, it is recommended to pad the
trench with sand to avoid damage to the pipe wall caused by soil swelling and stone
pressure.

42. DRIP IRRIGATION
31
Table 10. Internal diameter and wall thickness of PVC pipes
PN------> 60 m 80 m 100 m
OD - mm ID - mm Wall thickness -
mm
ID - mm Wall thickness -
mm
ID - mm Wall thickness -
mm
63 59.0 2.0 58.2 2.4 57.0 3.0
75 70.4 2.3 69.2 2.9 67.8 3.6
90 84.4 2.8 83.0 3.5 81.4 4.3
110 103.2 3.4 101.6 4.2 99.4 5.3
140 131.4 4.3 129.2 5.4 126.6 6.7
160 150.2 4.9 147.6 6.2 144.6 7.7
225 210.2 6.9 207.8 8.6 203.4 10.8
280 262.8 8.6 258.6 10.7 253.2 13.4
315 295.6 9.7 290.8 12.1 285.0 15.0
355 333.2 10.9 327.8 13.6 321.2 16.9
400 375.4 12.3 369.4 15.3 361.8 19.1
450 422.4 13.8 415.6 17.2 407.0 21.5
500 469.4 15.3 461.8 19.1 452.2 23.9
Lay-Flat Hoses
Flexible PVC lay-flat hoses can be used as mainlines and sub-mains. The hose is
impregnated with anti-UV radiation protecting agents. When the water is shut-off, the
hose lays flat on the ground and can be crossed-over by tractors and other farm
machinery. The lay-flat hoses can be laid out on the soil surface or in a shallow
trench. These hoses are available in diameters of 75 – 200 mm.
Fiberglass Pipes
In addition to UPVC and HDPE pipes, reinforced fiberglass pipes are used to deliver
water under high pressure from the water source to the irrigated area, as a
substitution for steel and asbestos-cement pipes.
GRP (Glass Reinforced Polyester) fiberglass pipes are manufactured in diameters of
300 – 3600 mm and PN grades of 40 – 250 m. They are particularly useful in delivery
of reclaimed water.
External and Internal Pipe Diameter
The internal diameter (ID) of a pipe can be calculated by deducting twice the wall
thickness from the external diameter (OD). In most cases, the nominal pipe diameter
(ND) is the same as its external diameter. Friction head losses of water flow in the
pipe are determined by the internal diameter.
When using nomograms, on-line calculators and design software it is important to
check whether the designated diameter is nominal (mostly external) or internal.

43. DRIP IRRIGATION
32
Chapter 7. DRIPPER TYPES, STRUCTURE, FUNCTION AND PROPERTIES
Introduction
The dripper is the core of the drip irrigation system. Drippers are small water emitters,
made of plastic materials. The design and production of high quality drippers is a
delicate and complicated process. Manufacturing the most effective dripper commits
compromising, taking into account diverse and contradicting demands.
The most important attribute of a dripper is low flow-rate, in the range of 0.1 - 8 liter
per hour (l/h). This low flow-rate can be obtained by different methods. Flow-rate is
determined by the pattern and the dimensions of the water passageway, as well as
the water pressure at the dripper inlet. The smaller the passageway cross-section,
the lower the dripper flow-rate at a given pressure. However, the narrower the
passageway the greater the risk of clogging by suspended solid particles and
chemical precipitates.
Since the water pressure at the dripper's outlet is a key factor in determining flow
rate, reducing that pressure may facilitate a low flow rate through a relatively wide
water outlet. Pressure reduction is achieved by diverse means.
Water passageway pattern: Historically, the initial method for pressure reduction
was a long flow passageway along a tiny micro-tube. Water friction against the wall
of the micro-tube resulted in substantial head losses. The factors affecting the degree
of head loss are: micro-tube length and diameter, micro-tube wall smoothness, flow
pattern and velocity. Initially, the micro-tubes were attached to a lateral and delivered
water at the desired application point. Later, the micro-tubes were wrapped around
the lateral and finally, drippers with internal built-in spiral water passageways were
constructed. The laminar passageway was problematic. The long water path and low
flow velocity led to the precipitation of chemicals that changed the dripper's flow-rate
or plugged it completely.
The labyrinth passageway is a
more advanced design. The water
flows along a labyrinth wherein
the flow direction changes
intermittently and gets a turbulent
pattern with high head losses
along a significantly shorter path
as compared to the spiral dripper,
resulting in the manufacture of
smaller and cheaper drippers. An
additional advantage of this
design is the lower accumulation
of dirt - particles and chemical
precipitations. Later designs
modified the labyrinth
passageway into a zigzag toothed
path with more efficient pressure
dissipation and self-cleaning
attributes. An advanced refinement of the toothed passageway is the turbonet (by
"Netafim") that enables shortening and widening of the water path even further.
Initial
laminar
design
Laminar
spiral
dripper
Labyrinth
passageway
Toothed
(zigzag)
passageway
Turbonet
passageway
Fig. 22. Evolution of the passageway style Courtesy “Netafim”

44. DRIP IRRIGATION
33
Turbulent flow has a cleaning effect in the
corners of the water passageways.
The vortex design is another method for
significantly dissipating pressure along a short
passageway. The water enters tangentially into
the dripper and flows in a spiral whirlpool pattern
with high head losses along a short path and
improved prevention of precipitates.
Another type of dripper
is the orifice dripper.
Pressure dissipation
occurs at the tiny water
inlet into the dripper.
The shortening of the
labyrinth passageways
enables fabrication of
small and cheap button
labyrinth drippers.
Along with the development of the discrete dripper
technology, a different concept - the trickling tape was
developed. The first product was a perforated plastic tube.
In order to obtain low discharge, the water outlets were tiny
and highly sensitive to clogging. This flaw was eliminated
later by the molding of long labyrinth water passageways
into the tube.
Fig. 27 Tape dripper lateral: empty (left) and filled with water (right) Adapted from "T-Tape" brochure
Dripper systems are classified according to various parameters:
Lateral Location
On-Surface Drip Irrigation
This is the prevalent drip technology. It enables convenient monitoring of dripper's
clogging and other disturbances during operation. On the other hand, this method is
susceptible to mechanical damage and degradation by solar radiation; it may
interfere with some farming activities and commits laying out and retrieving the
laterals when irrigating annual crops. In vineyards and some other deciduous
orchards (of apples and pears) grown at the palmeta pruning shape, laterals are
attached to trellises, improving the monitoring of drippers function and decreasing the
hazard of mechanical damage.
Fig. 23. Turbulent flow from "DIS" brochure
Fig. 25. Vortex dripper Adapted from
Karmeli & Keller, 1975
Fig. 24. Orifice dripper
Adapted from Karmeli & Keller, 1975
Fig. 26. Labyrinth
button dripper (“Netafim”)

45. DRIP IRRIGATION
34
Subsurface Drip Irrigation (SDI)
This technology has gathered momentum during the last two decades. Although the
system imposes extra costs for burying the laterals into the soil, this technology
simplifies irrigation operation and minimizes interference with other farm activities.
SDI has better water savings and nutrient utilization attributes than on-surface drip
irrigation. It also decreases infestation by weeds. Dripper clogging by root intrusion
and suction of soil particles may hinder proper function and must be avoided by the
proper selection of equipment, competent installation and strict routine maintenance
practices.
Layout of Water Outlets along the Lateral
There are two typical arrangements of drippers on laterals that affect the pattern of
water distribution in the soil.
Point Sources
Drippers are installed along the lateral with a spacing that creates a discrete wetted
soil volume by each emitter, without overlapping by the adjacent drippers. This layout
is mostly prevalent with thick wall laterals irrigating orchards and in annuals grown in
ample spacing.
Fig. 28. Point-source (left) and line-source (right) wetting by drippers
Line Sources
In a different layout, the drippers are installed along the lateral closed to each other
so that the wetted soil volumes of adjacent drippers along the lateral overlap. This
arrangement is typical with tapes and is the preferred alternative for densely grown
annual crops.
Lateral Type
Thick-Walled Laterals
Thick-walled laterals are made of Low Density Polyethylene Pipes (LDPE) with 12 –
25 mm external diameter and 1 – 2 mm wall thickness. The discrete drippers are
installed on-line or inline, 10 – 100 cm apart. The working pressure (PN) is 1 – 4 bar
(10 – 40 m).
Thin-Walled Laterals
Thin-walled laterals are also made of LDPE, however, the wall thickness is only 0.1 –
0.5 mm and the PN is 0.1 – 1 bar (1 – 10 m). Laterals may have discrete drippers
that are molded or inserted in the lateral. A different design is contiguous pressure
dissipation passageways as integral components of a tape.

46. DRIP IRRIGATION
35
Structure and Water Passageway Characteristics
As mentioned in the introductory section, the main objectives of the different dripper's
designs is the dissipation of pressure that renders low flow-rates, with minimal
clogging hazard and a cheap emitter. These objectives are achieved by different
methods, as is indicated below.
Long Path
The water flows through a long and narrow micro-tube. The micro-tube may be a
long one (spaghetti) or a built-in spiral in the dripper's body. Water flow is laminar and
the friction with the tube walls and the internal friction between water molecules
results in pressure dissipation. The discharge (flow-rate) of laminar-flow drippers is
highly sensitive to changes in pressure.
Fig. 29 In-line barbed laminar dripper (left, "Netafim") and turbulent in-line integral dripper (right,
"Drip-In")
Labyrinth Path
The water flows through a labyrinth that abruptly changes its direction, causing
turbulence. The frequent change of direction within the labyrinth results in high-
energy losses reducing the flow-rate along a relatively wide flow path. This pattern is
more effective in pressure dissipation than the laminar passageway. It enables using
wider water passages and reduces chemical and particle precipitations. The flow-rate
is less affected by changes in pressure in comparison to laminar flow.
Zigzag (Toothed) Path
The shape of the passageway is similar to the labyrinth path. However, the zigzag
flow dissipates more pressure in a shorter path and decreases clogging hazard.
Vortex
The water enters tangentially into vortex drippers. The water stream hits the walls of
the circular chamber, spins and looses energy. This allows for a relatively short flow-
path and wide-outlet orifice.
Orifice
The emitter flow rate is determined by the diameter of the orifice. This requires a tiny
aperture that increases clogging hazard.
Location on Lateral
Drippers can be installed externally on the lateral or inserted in-line.
Fig. 30. On-line drippers Courtesy “Netafim”

47. DRIP IRRIGATION
36
On-Line
On-line drippers are inserted into the lateral through punched holes. Drippers can be
added along time according to changes in crop growth and water requirements. The
dripper protrudes from the lateral, making it
sensitive to damage in delivery, installation
and retrieval (when applicable). The
dripper has a barbed or threaded joint that
is inserted or screwed into thick-wall
laterals.
In-Line
In-line drippers keep the outer face of the
lateral smooth. There are two versions:
In-line built-in drippers are fused into the lateral during the extrusion process.
Barbed In-line drippers are installed by cutting the lateral and inserting the barbs
into the cut ends of the lateral.
Distinctive Properties
Adjustable Drippers
The flow-rate of these drippers can be
adjusted according to the changing
requirements along the growing season.
Flag Emitters
These drippers have a twist opening locker
that eases the cleaning of fully or partially
clogged drippers during irrigation.
Pressure Compensated (PC) Drippers
The flow-rate of compensated emitters remains uniform provided the available
pressure is above a given minimum regulation pressure. There are several
compensating mechanisms that narrow or lengthen the internal water passageway
when the pressure rises, increasing head losses and keeping the flow rate constant.
Flexible Membrane above Water Path
The compensating mechanism is a
flexible diaphragm. As the pressure on
top of the diaphragm increases it narrows
the water passageway below the
diaphragm, increasing the head losses
and decreasing the flow-rate.
Thread Barb
Fig. 31. Button drippers conector design
Fig. 32. Adjustable
dripper (above) and flag
dripper (right)
Fig. 34. Button and inline PC drippers
Courtesy "Netafim"
Fig. 33. Flexible diaphragm under pressure

48. DRIP IRRIGATION
37
Changing of Water Flow Path Length
In another technique, pressure
compensation is applied by varying the
effective length of the labyrinth. The higher
the pressure the longer the effective
passageway. This is accomplished by
changing the number of openings between a
membrane and the labyrinth. These
openings are sequentially closed by an
increase in the pressure, maintaining the
discharge constant. The shortened water passageway, supported by this technology,
decreases clogging hazards and renders an efficient compensating mechanism.
Fig. 36. Change of water passageway length under high pressure - “Mezerplas” ADI PC Dripper
Non-Leakage (No Drain) Drippers
Drainage of drip laterals after water shutdown promotes accumulation of precipitates
at the bottom of the laterals and in the water passageways within the drippers. It lasts
some time after the beginning of irrigation until the laterals are full with water and the
required working pressure builds-up. During this time interval, the discharge of the
drippers in the initial part of the lateral is significantly higher than that of the drippers
at the distal end of the lateral. Frequent small water applications, as in vegetables
cropping, makes this time segment a significant fraction of the irrigation time length.
This results in significant difference in
water dosage between the initial and the
distal ends of the laterals and in the plot as
a whole.
The non-leakage drippers keep the lateral
full of water after shutdown by sealing the
dripper's outlet as the pressure drops. It
also facilitates fast pressure build-up in the
laterals at the start of the next irrigation.
Woodpecker Drippers
These drippers are designed for use in
plots prone to woodpecker’s damage. The
woodpeckers drill holes in the LDPE
laterals in search of water. Preventive
action is taken by burying the laterals with
the woodpecker drippers underground and connecting thin micro-tubes to the dripper
outlet. The distal end of the micro-tube is laid on the soil surface.
Woodpecker damage can also be reduced by distributing water-filled cans in the plot
to satisfy the woodpeckers’ thirst.
Fig. 35. ADI PC dripper From "Mezerplas" brochure
Bug cover Woodpecker
Fig. 37. Woodpecker drippers

49. DRIP IRRIGATION
38
Flap Equipped Drippers
Drippers equipped with a flap on the water outlet
prevent the suction of small soil particles into the
dripper at shutdown as well as the intrusion of roots
into drip lateral installed below the soil surface.
Treflan Impregnated Drippers
For long-term prevention of root intrusion into
subsurface drip laterals, the herbicide Trifluraline (TreflanTM
) is impregnated into the
drippers during the production process. After installation of subsurface laterals, small
amount of the herbicide is released with each water application into the soil around
the dripper, sterilizing its immediate vicinity. Drippers containing Trifluraline can
substitute routine Treflan application for up to 15 years.
Arrow Drippers
Arrow dippers are used for the irrigation of potted plants. The stick-like dripper is
inserted into the bed inside the pot. A high capacity built-in filter and efficient zigzag
turbulent water passageway keep the tiny dripper clean and reliable in long-term use.
Multi-Outlet Drippers
Each dripper has 2 – 12 outlets onto which small diameter micro-
tubes are connected. These drippers are used mostly in
landscaping and potted plants irrigation.
Ultra Low-Volume Drippers
Extremely low water application rates, in the range of 0.1 – 0.3 l/h per dripper,
change the water distribution pattern in the soil and the water-to-air ratio in the
wetted soil volume. The horizontal movement is more pronounced than with drippers
of conventional flow-rate range. Therefore, water can be applied to shallow root
systems with minimized drainage beneath the root-zone.
Fig. 38 Flap equipped dripper
Fig. 39. Arrow dripper for greenhouses, nurseries and pot plants Courtesy "Netafim"
Fig. 40 Six outlets

50. DRIP IRRIGATION
39
Due to the extremely low water
discharge from the emitters, more
air remains in the wetted volume,
compared with drippers of
conventional flow-rate.
Extremely low flow-rate drippers are
sensitive to clogging because of the
narrow water passageways and low
flow velocity. There are two
technologies to achieve low flow-
rate with minimal clogging hazard.
One technology is based on
conventional button drippers that
emit water into a secondary small
diameter with 10 – 30 molded or inserted micro-drippers. In the second technology,
conventional drip laterals are used but the water is applied in pulses created by
pulsators or by the irrigation controller. Because of the relatively short pulses and
long intervals between them, drippers should be of the non-leakage (no drain) type.
Integral Filtration in Drippers
High quality drippers have built-in
small integral filters to reduce the
clogging hazard of the water
passageways and guarantee proper
function of the complicated
mechanisms needed for pressure
compensation, drainage prevention,
etc. The filtering area is increased
to ensure long-term performance.
Additional anti-clogging means are dual water inlets and outlets in the single dripper
and the barbs in on-line drippers which protrude into the lateral so that the water inlet
is kept away from the dirt that accumulates on the lateral's walls. Anti-siphon devices
such as the above-mentioned flaps also decrease clogging hazard.
Static state Pressure compensation Flushing
Fig. 43. Auto flushing, pressure compensating dripper Courtesy "Netafim"
Auto Flushing Mechanisms
In some of the compensated drippers, a flexible diaphragm is used to release debris
that clogs the dripper. When a solid particle blocks the water path, the diaphragm is
arched, widens the passageway and releases the clogging object.
Fig. 41. Ultra low flow micro-drippers
Adapted from "Plastro" brochure
Fig, 42. Integral filters Courtesy "Netafim"

51. DRIP IRRIGATION
40
Chapter 8. ACCESSORIES
In addition to drippers and pipes, drip irrigation systems are comprised of diverse
accessories. Wise selection of these components can guarantee optimal long-term
performance of the system.
These accessories can be classified in four categories:
Connectors: connecting pipelines and laterals to the regulating and control
devices, interconnecting pipes of different types and diameters, laterals to
manifolds and drippers to laterals.
Control, monitoring and regulation devices: valves, filters, water meters,
pressure gauges, etc.
Chemicals injectors and safety devices.
Soil moisture measuring and monitoring instrumentation.
Connectors
Connectors are made of metal or plastic materials. They may be two-sided straight-
through or angular units, T or Y pattern triple outlets, four-sided crosses or multi-
outlet splitters.
Fig, 44. Plastic and metal pipe and lateral connectors
Connectors to control devices are usually threaded or flanged. Connectors between
pipes and laterals are mostly barbed or conic. There are simple barb connectors,
while more sophisticated connectors have an inner barb and external fastening cap.
HDPE pipes may be joined by heat fusion in the field. If done properly, fusion is
reliable and durable.

52. DRIP IRRIGATION
41
Control Devices
Valves are basic control devices. There are
different types of valves, each of which
performs a different task.
Gate valves are used for on-off tasks.
They are not suitable for gradual opening
and closing tasks.
Ball valves are also used for on-off tasks.
They have low head losses but are not
suitable for flow regulation.
Globe valves have higher head losses but
they are efficient and precise for flow
regulation.
Angular and Y shaped valves have lower
head losses than globe valves and they
can also be used for flow regulation.
Butterfly valves have modest head losses and certain throttling capability.
Hydraulic valves appear in most of the before mentioned designs. They have a
control chamber in which water pressure from the command line actuates a piston or
diaphragm that regulate the flow through the valve by narrowing or expanding the
water passageway.
Hydraulic valves are of two types: normally open (N.O.) and normally closed (N.C.).
Normally open (N.O.) valves remain open until the control chamber is filled with water
under the system’s pressure, to close it
Normally closed (N.C.) valves remain closed by the water pressure in the main-line.
The closure is secured by a spring, in case of a rupture in the command line. In order
to open the hydraulic valve, the controller opens a small valve at the top of the
control chamber, releasing the pressure exerted on the diaphragm.
Fig. 45. Lateral start, plugs and lateral end Fig. 46. Reinforced connectors
Fig. 47. Drip laterals connectors and splitters

53. DRIP IRRIGATION
42
The pressure which the water in the system exerts on the
lower face of the diaphragm reopens the valve.
Normally closed hydraulic valves have higher head losses,
but they are safer to use, as the valve remains closed even if
the command tube is torn or plugged.
Water meters are essential for accurate water application.
The most prevalent are the Woltmann models. Bi-annual re-
calibration is required.
Pressure regulators are used to maintain a constant
downstream pressure, independent of upstream fluctuations
provided it remains above the regulating pressure.
Pressure regulation is particularly important for drip irrigation.
Thin walled laterals have PN of 4 – 15 m, and burst at higher
pressures. When using non-compensated drippers, pressure
regulators installed on the manifolds or lateral heads can
maintain uniform pressure under harsh topographic
conditions.
There are two types of pressure regulators. Simple
mechanical devices regulate the pressure against a spring,
Fig. 48. Hydraulic valve
Fig. 49. Spring pressure
regulator assemblies
Courtesy "Netafim"

54. DRIP IRRIGATION
43
while in the more sophisticated devices the pressure is controlled hydraulically by a
diaphragm or piston.
Fig. 50. Spring actuated pressure regulator Fig. 51. Hydraulic pressure regulator
Metering Valves
The metering valve is a combination of a water meter with a hydraulic valve. The
desired volume of water to be applied is dialed in. The valve opens and closes
automatically only after the assigned volume has been delivered.
Metering valves are used extensively in drip irrigation. They facilitate also the gradual
opening and closing of water, which is important to avoid the collapse of thin-walled
laterals. They are handily compatible with automation.
Fig. 52. Horizontal and angular metering valves

55. DRIP IRRIGATION
44
The actuator in the metering valve can be a diaphragm or a piston. A diaphragm is
less sensitive to dirt in the water, but can be torn in high pressure fluctuations and
may wear due to chemical degradation.
Electric Valves
Electric valves are vastly used in automation. They
are operated by a solenoid that converts electric
pulse to mechanical move. In a small diameter – up
to 1” (25 mm) – the solenoid can serve as direct
actuator. In wider diameters, the solenoid commands
hydraulic actuators. Energy sources are AC current
where applicable, batteries and solar cells.
Pressure relief valves have the task to instantly
release water under excess pressure in order to
protect the system. They can be mechanical, working
against a spring (cheaper but less reliable) or
hydraulic devices.
Air relief valves are used to release air from the
pipelines during filling with water and to let air in
when pipelines on slopes drain. Plastic pipes,
manufactured to withstand a pressure of 6, 10 or
more bars, are seriously damaged when the pressure inside the pipe falls below
atmospheric pressure. “Double action" air relief valves let air escape even when the
floating device is lifted by pressure buildup as the pipeline fills with water.
Air Relief Valves and Vacuum Breakers
Fig. 54. Air-relief valves
As mentioned before, air relief valves and atmospheric vacuum breakers are
essential components of the drip irrigation system.
There are three types of air relief valves:
Fig. 53. Electric valve "Bermad"

56. DRIP IRRIGATION
45
Automatic valve: releases small volumes of air during ordinary operating conditions.
Kinetic valve: releases large volumes of air while the system is filled with water and
allows a great volume of air to enter the system at shutdown.
Combination valves: Automatic and kinetic valves mounted together in one
assembly.
Atmospheric vacuum breakers are
small devices, ½” – 1” in diameter that
break the vacuum at water shutdown
and do not allow air to escape from the
system when water drains from the
irrigation system and the pressure in the
pipelines falls below the atmospheric
pressure.
Air relief valves introduce air into the
irrigation system when its pressure equals or falls below the atmospheric pressure
and function as vacuum breakers.
Check-Valves and Backflow Preventers
These valves are used to prevent backflow from the irrigation network to the water
supply network, when that network supplies potable water to consumers. These
devices are described in the chapter on fertigation.
Lateral-End Flush Devices
In drip irrigation, a vast amount of precipitates is accumulated in the lateral distal end.
The automatic lateral end flush device releases water at the start of irrigation, before
working pressure builds-up in the system. This performs routine flushing of the
laterals, eliminating the need to do it manually.
Fig. 55. Atmospheric vacuum breakers
Fig. 56. Lateral-end flushing action

57. DRIP IRRIGATION
46
Chapter 9. FILTRATION
Due to the narrow water passageways and low water-flow velocity in the drippers,
drip systems are sensitive to clogging. Clogging prevention requires high-level
filtration and complimentary chemical and physical water treatments.
Table 12. Characteristics of water passages in drippers (example)
Water passageway Water passagewayFlow
Rate* Length Width Depth Cross
section
Flow
rate Length Width Depth Cross
section
Non-
compensated
drippers
l/h mm mm mm .mm2
Compensated
drippers
L/h mm mm mm mm2
Inline 8.0 220 1.95 1.84 2.80 PC button 8.0 13 1.39 1.45 2.00
Button 8.0 48 1.39 1.45 2.02 ” 4.0 60 1.39 1.49 2.07
Inline 4.1 258 1.35 1.45 1.95 “ 2.0 60 1.25 1.09 1.38
Button 3.8 50 1.15 1.05 1.22 Ram PC 3.5 15 1.22 1.22 1.46
Tiran 4.0 95 1.38 1.38 1.90 “ 2.3 15 1.04 1.04 1.08
Typhoon 2.8 17 0.81 0.81 0.65 “ 1.6 19 1.00 1.00 1.00
Tiran 2.0 135 1.00 1.00 1.00 “ 1.2 19 0.91 0.91 0.83
Inline 2.0 280 1.10 1.18 1.30 Midi button
PC
4.0 30 1.20 1.25 1.50
Button 2.0 53 0.90 0.80 0.72 “ 2.0 32 0.98 1.00 0.98
Typhoon 1.75 20 0.71 0.71 0.5
* In non-compensated drippers – nominal flow rate at 1 bar (10 m) pressure head. Courtesy “Netafim”
Impurities in water can be classified in four categories:
Inorganic suspended solids: sand, silt, clay and gravel.
Dissolved chemicals that precipitate from the water in certain
circumstances. The most prevalent chemical precipitates are calcium carbonate,
calcium phosphates and calcium sulfate (gypsum). Dissolved iron and hydrogen
sulfide enhance development of bacteria population that clogs drippers, filtering
media and command micro-tubes.
Live organic material: zooplankton and phytoplankton - algae, protozoa,
bacteria and fungi. Live organisms can propagate rapidly in suitable conditions
and excrete sticky mucus material with enormous clogging potency.
Organic debris
The most contaminated waters are raw sewage and low-quality reclaimed water.
Water pumped from ponds, lakes, rivers, streams, canals and dam reservoirs, also
contains a high load of impurities. Water pumped from sand aquifers contains a
relatively high amount of suspended sand.
There are diverse filtering methods using different filtering media: screens, grooved
discs, gravel and sand. Sand and silt separation is often performed as a pre-
treatment in settling ponds and tanks or by means of centrifugal separators. In
greenhouses with detached growing media, in which drainage water is recycled for
reuse in irrigation, slow sand filter systems are used to eliminate water-borne
pathogens.

58. DRIP IRRIGATION
47
Screen (Strainer) Filters
There are different types of screen filters. The most
important properties of a screen filter are filtration
degree, filtration surface area and filtration ratio.
Filtration degree is defined with two systems of
units: microns and mesh number. The filtration
degree in microns designates the diameter of the
biggest ball-shaped particle that can pass between
the screen wires. The mesh number counts the
number of wires along 1" (25.4 mm) length of the
screen. The two definition procedures are not fully
inter-convertable. Holes width may differ in two
screens with the same mesh number due to a
difference in wire thickness. Rough conversion from
one system to another is made using the rule of
thumb: mesh number x microns = 15,000.
When selecting the filtration degree, both the
dimensions of the water passageways in the dripper
and the character of water impurities should be
considered. When the impurities are suspended
inorganic solids (sand, silt, chemical precipitates), the maximum
perforation diameter should be 25%-30%
of the width of the emitter’s narrowest
water passageway. When the impurities
are organic and biological materials, the
maximum perforation diameter should be
no more than 10%-20% of the water
passageway width. Screen filters are
most suitable for water with inorganic
impurities, while high loads of organic
and biological impurities may quickly clog
the screen.
Fig. 58. Head losses in clean screen filters Adapted from "Odis" brochure
One of the main disadvantages of screen filters is the fast accumulation of dirt on the
screen's surface. The accumulated dirt increases the head losses and may cause the
Fig. 57. Screen filter
Table 13. Screen Perforation – Examples
Mesh no. Hole size –
microns
Wire thickness
- microns
40 420 250
50 300 188
80 177 119
100 149 102
120 125 86
155 100 66
200 74 53

59. DRIP IRRIGATION
48
collapse of the screen. Excess dirt accumulation should be prevented by monitoring
the pressure difference between the filter inlet and outlet and cleaning the screen
when the difference is greater than 5 m head.
Disc Filters
Disc filters are the favored choice for filtration of water containing mixed impurities -
inorganic solid particles and organic debris. The casing is made of metal or plastic
materials. The filtering element is made of a stack of grooved rings, tightened firmly
by a screwed cap or a spring with a water-piston. Water is filtered as it flows through
the grooves. The intersections of the grooves provide in-depth filtering. Coarse
particles are trapped on the external surface of the stack. Finer particles and organic
debris remain in the inner grooves. The disc filter has a significantly higher dirt-
retention capacity than screen filters. The definition of the filtration degree is identical
to that of screen filters and is mostly indicated by the color of the discs.
Fig. 59. Disc filter
Media Filters
Media filters are used to
protect the drippers when
using water with a high organic
load from open water bodies
or reclaimed water. Wide-
body (0.5 - 1.25 m in diameter)
media containers are made of
epoxy-coated carbon steel,
stainless steel or fiberglass.
The filtering media are 1.5 - 4 size mm basalt, gravel, crushed
granite particles or fine silica sand. The organic impurities
adhere to the surface of the media particles. The accumulated
dirt should be back-flushed routinely in order to eliminate
excessive head losses. The filtration degree is defined
according to that of screen and disc filters.
Sand Separators
High loads of sand and other solid particles should be removed
before reaching the main filtration system.
Table 14. Sand particle size and mesh equivalent
Sand No. Effective sand
size – mm
Mesh equivalent
range
Crushed Silica 12 1.1. – 1.2 80 - 130
Standard Sand 6/20 0.9 – 1.0 100 - 140
Crushed Silica 16 0.6 – 0.7 155 - 200
U.S. Silica 80 0.6 – 0.7 160 - 200
Crushed Silica 20 0.28 170 - 230
Fig. 60. Media filter

60. DRIP IRRIGATION
49
There are two methods of sand separation.
The traditional practice is based on sedimentation of solid
particles from the water by slowing down its flow in
settling tanks or basins. Closed tanks conserve the water
head while the use of open settling basins requires re-
pumping of the treated water into the irrigation system.
Contemporary technology employs centrifugal sand
separators that sediment sand and other suspended
particles that are heavier than water by means of the
centrifugal force created by the tangential flow of water
into a conical container. The sand particles are thrown
against the walls of the container by the centrifugal force,
settle down and accumulate in a collecting chamber at
the bottom. The collector is washed out manually or
automatically when full. Clean water exits through an outlet at the top of the
separator. Each type of separator (designated by the diameter of the inlet and outlet)
has an optimal flow-rate range in which the most of the suspended particles are
removed without excessive head-losses. At lower flow rates, more sand remains
suspended in the water.
Fig. 62. Hydro-cyclone sand separator – head losses and optimal flow rates From "Odis" brochure
Filter Characteristics
Reliability
Disc filters are regarded as highly reliable. Collapse of the filtration element is rare
compared to screen filters. In screen filters, the screens are prone to tear and
collapse by corrosion and pressure fluctuations. The screen-supporting skeleton has
to withstand pressure surges.
Capacity and Head Losses
Water loses pressure as it flows through a filter. The extent of the head loss depends
on the filter's design, filtering degree, flow rate and the degree of dirt accumulation.
Normally, for a specific type and size of filter, the finer the filtration degree, the lower
Fig. 61. Sand separator

61. DRIP IRRIGATION
50
is the nominal discharge. This is due to higher head losses and faster dirt
accumulation.
Key filter properties:
Diameter: Designates the water inlet and outlet diameter.
Filtration area: The total surface area of the filtration element. The required filtration
area for moderately dirty water is 10 - 30 cm2
for each 1 m3
/h of discharge for
sprinkler irrigation, 25 - 60 cm2
for micro-jets and 60 - 150 cm2
for drip irrigation.
Perforation area: The total open area of the perforations.
Effective filtration ratio: The ratio between the perforation area and the filtration
area.
Filter ratio: The ratio between the perforation area and the inlet cross-section area.
The higher the above mentioned parameters, the higher the filter capacity. The
nominal capacity of other types of filters is defined according to the allowed head
losses.
Table 15. Nominal filter capacity – examples
Make Filter type &
diameter
Filtration grade-
microns
Capacity m3
/h
Odis 2” screen 60-400 15-25
Arkal 2” disc 100-400 25
Arkal 2” disc 75 16
Arkal 2” disc 25 8
Amiad 3” screen 80-300 50
Amiad 3” disc 100-250 50
Odis 4” screen 60-400 80
Netafim 4” gravel 60-200 60-120
Netafim 6” sand separator 140-230
Nominal filter capacity relates to the flow-rate at a head loss of 2 m (0.2 bar.) in a
clean filter. As dirt accumulates, head loss increases. Cleaning of the filter is
required when head loss reaches 5 m (0.5 bar). A minimal head loss of 1.5 m (0.15
bar) is required for adequate sand separation by hydro-cyclone sand separators. The
recommended head loss range in sand separators is 2.5 - 5 m (0.25 - 0.5 bar). When
the water flow-rate changes frequently, it is recommended to install an array of sand
separators in parallel, each equipped with a valve and connected to each other. The
number of units activated per each operation should be adjusted to the specific
discharge. Dirt accumulation capacity is lowest in screen filters, higher in disc filters
and highest in media (sand and gravel) filters.
Flow Direction
The direction of flow through the filtration element is an important feature. In disc
filters, water flows from the perimeter inwards. This pattern exposes the greater
external surface area of the discs stack that is able to retain a much greater quantity
of coarse particles than the smaller inner surface area could possibly do. However, in
screen filters, flow from the inside - out, is more suitable for self-cleaning

62. DRIP IRRIGATION
51
mechanisms and is less vulnerable to screen collapse by pressure surges. Some
models of screen filters have two filtering elements: the preliminary coarse strainer
that traps the coarse particles, and a finer screen for final filtration in the second
stage. Some filter designs include nozzles that induce the tangential flow of water
which drives the dirt to the distal end of the filter from where it can be flushed-out
intermittently or trickle out continuously.
Water enters into media filters from the top and exits from the bottom after crossing
the filtering media that lies on a perforated plate. Back-flushing is accomplished in
the opposite direction – from the bottom upwards. To facilitate proper back-flushing,
the media fills no more than 2/3 of the height of the tank, so that it may be lifted and
agitated during the back-flushing process.
The tangential flow of the water in sand separators invokes centrifugal forces, which
deposits the solid particles at the bottom of the separator. Clean water outlet is at
the top of the separator.
Operation and Maintenance
Routine cleaning of the filtration elements is crucial. The best indicator for the need
to clean the elements is the pressure differential between the inlet and the outlet of
the filter. The pressure differential increases as dirt accumulates on the filtration
element. In order to enable measurement of the pressure differential, nipples for
pressure measurement are mounted on the filter's inlet and outlet. The pressure is
monitored manually with a needle type pressure gauge or by connecting the two
nipples to a three-way valve, on which a fixed manometer is mounted. As mentioned
before, cleaning is recommended when the pressure differential reaches 0.5 bar (5
m). During manual cleaning, the integrity of the filtration elements should be
inspected. Particular attention should be paid to the seals, O-rings and their
mounting between filter casing and cover.
The grooved rings in disc filters should be flushed with water. The tightening screw
should be released to enable the water stream to separate the discs from one
another. Care should be taken not to drive the dirt into the water outlet and to tighten
the discs properly after cleaning the discs.
Automatic Flushing and Cleaning
Different mechanisms for automatic cleaning have been developed for the different
types of filters. Most of the procedures rely on measuring the pressure differential
and performing self-cleaning when a preset head differential has built-up. Another
method is timer-controlled intervals between flushings.

63. DRIP IRRIGATION
52
Self-flushing screen filters maintain a flow
of filtered water without build-up of head
loss. The dirt is continuously removed
from the screen by a tangential, spiraling
downward water flow, which flushes the
debris into a collecting chamber at the
distal end of the casing. The
accumulated dirt is drained manually,
continuously by a bleeder or
automatically when the preset water
difference between the water inlet and
outlet has been built. The cleaning
process lasts for a preset time. The
cleaning and flushing mechanism is
powered by the inherent pressure in the system or by an electric motor. Rotating
brushes or sucking nipples clean the screen. For relatively coarse screens, above
200-micron, brushes are efficient while for finer screens, under 200 microns, cleaning
by rotating suckers is preferred.
Automatic flushing of disc filters requires release of the disc stack. The Spin-Klin
mechanism combines back-flushing by water counter-flow, release of the stack
tightening screw and spinning of the separated discs by the water flow, which flushes
the dirt from the grooves, through an automatically opened draining valve.
Fig. 64. Automatic flushing of disk filters Adapted from "Arkal" Brochure
Media filters are fllushed automatically by back-flow from the bottom that floats the
accumulated dirt out through the drain valve. The reverse flow begins automatically
when the preset pressure differential has been attained.
Automatic flushing of media and disc filters requires the back-flow of filtered water.
To meet this requirement these filters are operated in arrays and the flushing of the
filters is sequential, one after another.
Fig. 63. Self-flushing screen filter

64. DRIP IRRIGATION
53
Fig. 65. High capacity media filters array Fig. 66. Back-flushing of media filters
Fig. 67. High capcity automatic filter Adapted from "Netafim" brochure

65. DRIP IRRIGATION
54
Fig. 68. Compact automatic filter Adapted from "Netafim" brochure
Filter Location
When surface water with a high load of impurities is pumped from rivers, streams,
canals or other open reservoirs, the pump site and depth of the suction pipe are
crucial. The suction port should be as far upwind as possible, since floating debris
and vegetation are blown downwind. The optimal pumping depth is beneath the
upper layer of floating vegetation (plankton) and other debris, but not too deep, in
order to verify an adequate concentration of dissolved oxygen in the pumped water.
When applicable, it is recommended to pump from a pumping chamber sheltered by
a coarse screen to protect the pump and avoid clogging of the suction inlet.
When the pumped water contains sand or other suspended solids, a settling tank
should be installed just ahead of the pump, or a sand separator just beyond the
pump, in order to prevent solid particles from entering the supply network.
In highly contaminated water, multi-stage filtration is required. An automatic screen,
disc, media filter or a filtration array should be installed at the pumping site, and
backup control screens or disc filters should be installed at the control valve at each
of the irrigated sectors.
With moderately contaminated deep-well water, one filtration stage at each sectorial
valve may be sufficient.

66. DRIP IRRIGATION
55
Slow Sand Filtration
The new trend of recycling the drainage water in greenhouses and nurseries for
reuse in irrigation, poses the hazard of infestation by soil-borne pathogens such as
Pythium and Phytophthora spp. Diverse procedures have been developed to deal
with this problem, like chlorination, ozone treatment, heating, ultraviolet (UV)
irradiation and others. These technologies are expensive and are economically viable
only at low flow rates of 5 – 10 m3
/h.
Fig 69. Slow sand filter Adapted from Htinik and Krause (1999).
The best cost effective solution is Slow Sand Filtration (SSF), first developed during
the late eighties at the State Research Station at Geisenheim, Germany. Today,
there are in use filtration systems with capacities as high as 50 m3
/h. The effective
flow rate is up to 100 – 200 l/h per 1 m2
of bed surface area. The efficiency of SSF
depends upon the particle size distribution of the sand, the ratio of the filter’s surface
area to its depth and the flow-rate of water through the filter. Fine-grade sand
fractions and granulated rock-wool have been shown to be most efficient in
controlling diseases such as Phytophthora, Pythium and Fusarium oxysporum, the
most widespread greenhouse diseases.
The SSF completely eliminates Pythiaceous fungi such as Phytophthora and
Pythium. Efficiency against bacteria and fungi with small spores is high; however
some propagation spores may pass the filter bed. Viruses and nematodes are not
satisfactorily eliminated by slow sand filtration.
Filters may be constructed in tanks with non-reactive surfaces such as plastic or
fiberglass, metallic galvanized tanks or concrete tanks of various capacities, from 200
liter up to 100,000 liter.
Before the water enters the SSF system, silt and organic matter should be removed
by sedimentation or centrifugation and chlorination. The pre-treated water is filtered

67. DRIP IRRIGATION
56
very slowly through a deep bed of sand. The maximum flow rate depends upon the
size of the microorganisms that have to be removed. A slow flow rate of 100 l/h per
m2
of surface area has been found to be preferable in high risk situations such as the
control of Fusarium or viruses in tomatoes. Rates of 200 or 300 l/h per m2
are
recommended for control of Pythium and Phytophthora when the risk of infestation is
low to medium. The grain size of the sand is 0.15 – 0.30 mm. (100 – 50 mesh
equivalent).
One to 4 weeks after the
beginning of filter operation,
a layer of brown material
("schmutzdecke") develops
in the upper 2 cm layer of
the bed. Pseudomonas,
Trichoderma, and other
microorganisms known as
bio-control agents in
compost-amended
container media seem to
slowly destroy the
pathogens that were
immobilized through
filtration in this layer. The filters are not effective until this layer develops. The
"schmutzdecke" layer has to remain intact. A layer of water one meter high is always
maintained on top of the filter's bed in order to avoid destruction of the schmutzdeke
– the upper active bed layer. Water can be added to the reservoir by sprinkling to
minimize turbulence.
The depth of the sand bed is 1 – 1.2 m. This depth allows periodic cleaning of the
filter by removal of the "schmutzdecke", when flow rates drop due to clogging.
Underneath the sand there are several layers of gravel and a drainage system. The
water layer above the filter bed provides the head to drive the water downwards
through the filter bed. It is used as a water storage zone and temperature buffer to
stabilize the filter and protect the biological activity in the top layers. The top layer will
never be allowed to dry. Continuous filtering supports the development and
maintenance of a healthy system
Some growers use rock-wool as a substitute for sand. Rock-wool is more expensive,
but with rock-wool as a filtering media, gravel is not needed for drainage at the
bottom of the filter.
The filtered water flows by gravity into a sealed concrete reservoir at the lowest point
of the filtration system. The filtered water is then pumped out of this reservoir to a
storage facility or directly into the irrigation system.
When the flow rate through the filter slows, due to increasing head losses, the water
layer above the sand bed should be drained and the top layer of sand with the
"schmutzdecke" scraped off. This layer should contain most of the organic matter and
silt that were slowing the water flow. Only the 1 – 2 cm upper "schmutzdecke" layer
will be scrapped for minimal removal of biomass.
Fig. 70. Slow Sand Filter scheme

68. DRIP IRRIGATION
57
Filter for SDI
"Netafim" supplies filters with disks that
are impregnated with the herbicide
TrIfluraline. The disks slowly release a
low concentration of the herbicide into
the irrigation water, preventing intrusion
of roots into the drippers. Effective
release lasts for 2-3 years, after which
the disk stack should be replaced.
Replacement disks are packed in
opaque bags, as Treflan (Trifluraline)
decomposes quickly when exposed to
light. Fig. 71. Treflan impregnated disk stack
Courtesy "Netafim"

69. DRIP IRRIGATION
58
Chapter 10. FERTIGATION
Because of the limited soil volume that is wetted by drip irrigation frequent water
applications are required. Plants absorb nutrients only from the wetted soil volume.
Hence, in order to avoid the loss of nutrients by deep percolation, fertilizers have to
be applied only to the wetted soil volume. The most efficient and convenient way to
accomplish this is to combine water and nutrient application in the same system. This
logic led to the development of fertigation technology.
The combined application of water and fertilizers through the irrigation system
increases yields and minimizes the hazard of environmental pollution by excess
fertilization. Chronologically, the development of the fertigation technology followed
the introduction and the development of drip irrigation in the early sixties.
There are several methods for injecting fertilizers into the irrigation system.
Fertilizer Tank
A pressure differential is created by partial throttling of
water flow with a valve and diverting a fraction of the flow
through a tank that contains the fertilizer solution. A
gradient of 0.1 – 0.2 bar (1 – 2 m) is required to divert an
adequate stream of water through a 9 – 12 mm diameter
tube. The tank, made of corrosion resistant enamel-
coated or galvanized cast iron, stainless steel or
fiberglass, has to withstand the working pressure of the
network. Solid soluble fertilizers or liquid fertilizers are
mixed with the flowing water. When using solid fertilizers,
the nutrient concentration remains more or less constant,
as long as a portion of the solid fertilizer remains in the
tank. After the full dissolution of the solid fertilizer, the
concentration of the injected solution decreases
gradually due to continuous dilution by the water. The
system is relatively simple and cheap. There is no need
for an external energy source and a wide dilution ratio
can be obtained. However, there are some drawbacks.
The fertilizer injection rate and nutrient concentration in
the irrigation water cannot be precisely regulated. The
tank has to be refilled with fertilizer before each
application. Valve throttling generates pressure losses
and the system is not easily compatible with automation.
Venturi
When water flows through a constricted passageway,
suction is created. The high flow velocity of water in the
constriction reduces the water pressure below the
atmospheric pressure so that fertilizer solution from an
open tank is suctioned into the constriction through a
small diameter tube.
Venturi devices are made of corrosion-resistant
materials, such as copper, brass, plastic and stainless steel. The injection rate of the
Fig. 72 Fertilizer tank From
"Odis" brochure
Fig. 73. Venturi injector

70. DRIP IRRIGATION
59
Venturi device depends upon the pressure loss, which ranges from 10% - 75% of the
system's pressure and is determined by the injector type and operating conditions.
Operation of Venturi devices requires excess pressure to allow for the necessary
pressure loss. Maintaining a constant pressure in the irrigation system guarantees
uniform nutrient concentration over time. Common head losses are above 33% of the
inlet pressure. Use of double stage Venturi injectors decreases the pressure loss to
10%. The suction rate depends on the inlet pressure, pressure loss and diameter of
the water pipe. It may be adjusted by valves and regulators. The suction rate varies
from 0.1 l/h to 2000 l/h. Venturi injectors are installed in-line or on a by-pass. In
greenhouses, the water flow in the bypass can be boosted by an auxiliary pump.
The advantages of a Venturi system are: no external energy source is required;
cheap open tanks may be used; wide range of suction rates; simple operation and
low wear; easy installation and mobility; compatibility with automation; uniform
nutrient concentration; corrosion resistance. Limitations of the system are: significant
pressure losses; injection rates affected by pressure fluctuations.
Injection Pumps
Fertilizer injection pumps can be driven by electricity, internal combustion engines,
tractor PTO or hydraulically by the irrigation system’s inherent water pressure.
Hydraulic pumps are versatile, reliable and have low operation and maintenance
costs. Diaphragm and piston hydraulic pumps are driven by the pressure of the
irrigation system. Some types cast a fraction of the propelling water after its energy
has been dissipated. Centrifugal pumps are used when high capacity is needed or
the fertilizer solution is turbid. Roller pumps are used for the precise injection of small
amounts of nutrient solution but have a short life span due to corrosion by the
chemicals. Water driven diaphragm and piston pumps combine precision, reliability
and low maintenance costs.
Pumps used in fertigation are mostly automatically controlled. A pulse transmitter is
mounted on the pump. The movement of the piston or the diaphragm sends electrical
signals to the controller and indicate amount of water delivered. Measurement of the
injected solution volume can also be performed by small fertilizer-meters installed on
the injection tube. The controller allocates the volume of fertilizer solution according
to preset program. Dosing is proportional or quantitative. With proportional dosing,
Fig. 74. Piston (left) and diaphragm (right) hydraulic pumps From
"Amiad" Brochure
Fig. 75. No-drain hydraulic
pump From "Dosatron" brichure

71. DRIP IRRIGATION
60
fertilizer is injected into the irrigation water at a constant ratio. In the quantitative
mode, a preset amount of fertilizer solution is injected in short pulses during the
irrigation period.
In glasshouses, simultaneous
application of a multi-nutrient solution
is routine. When the distinct chemical
compounds in the fertilizers are
incompatible and cannot be mixed
together in a concentrated solution,
due to risk of decomposition or
precipitation, two or three injectors are
installed in-line in the control head. The
application ratio between the different
injectors is coordinated and monitored
by the irrigation controller.
More sophisticated device used in glasshouses of high-income crops grown on
detached media and irrigated by circulating drainage water. In these circumstances,
the irrigation water is mixed with fertilizers in a mixing chamber (mixer). The mixture
is pumped into the irrigation system as it.
Electric Pumps
Electric pumps are inexpensive and reliable, operation costs
are low and they are readily integrated into automatic
systems. A wide range of pumps is available, from small,
low-capacity pumps to massive, high-capacity pumps. Some
pumps are based on an alternating displacement diaphragm.
Others employ a positive-displacement piston unit, with a
single-phase AC motor as the primary power source. The
working pressure is 1 - 10 bars. As a standard fitting,
diaphragm pumps have a separation chamber and seal that
prevent the nutrient solution from flooding the motor and the electromagnetic drive if
the diaphragm ruptures.
Electric piston pumps are highly precise. They are suitable for accurate mixing in
constant proportions of different stock solutions. Variable speed motors as well as
variable stroke length allow a wide range of dosing. Capacities are 0.5 to 300 L/h and
working pressure is 2 - 10 bars.
Fertigation Management
The timing of fertilizer application should be attuned to the irrigation schedule. Dosing
is determined according to experimental and analytical results. The inherent
concentration of nutrients in the irrigation water should be taken into account.
Injection Site
The fertilizer solution can be injected into the irrigation system at the control head of
each plot. Such an assembly requires an injection device for each plot, and the total
cost may be higher than that for a single central injection site. Another option for
fertilizer injection is at the head of a sub-main and this is a common practice for field
crops. The most convenient, and in many cases the cheapest alternative is fertilizer
Fig. 76. Mixer
Fig. 77. Electric pump

72. DRIP IRRIGATION
61
injection at the main control head. This saves labor and is more compatible with
automation.
Control and Automation
With quantitative dosing, a measured amount of fertilizer is injected into the irrigation
system during each water application. Injection may be initiated and controlled
automatically or manually. Proportional dosing is based on a predetermined ratio
between the irrigation water and the fertilizer solution. This is common with soil-less
cultures. It can be applied in a pulsating pattern. Pulses are regulated by
synchronization of signals delivered by pulse transmitters mounted on the injectors
those mounted on the metering valve. The fertilizer solution meter is a combination of
a small metering chamber and a magnetic affinity interrupter. Constant proportional
fertilization is essential with sandy soils and soil-less cultures.
Injection Timing
Fertigation may be applied during only one segment of an irrigation shift. In this case,
fertilizer is not applied at the beginning nor towards the end of the shift. This
procedure ensures build-up of the proper pressure before irrigation commences, and
flushing out of nutrient residues from the irrigation system towards the end of
irrigation. Fertilizer is injected quantitatively or proportionally.
Automatic Control
Automation facilitates the implementation of diverse fertigation regimes in one and
the same system without manual intervention. The main components of automation
hardware are:
(i) Solenoid: a command valve that converts electric pulses sent from an irrigation
controller or a field unit into mechanical motion. The mechanical motion activates
hydraulic valves. Some solenoids are AC and others DC. Common solenoids have 2
wires while “latching” solenoids may have 2 or 3 wires.
(ii) Controller: the controller unit coordinates and controls the fertigation process. For
proportional injection, the fertilizer solution is separated into small portions that are
injected at a predetermined ratio in coordination with the pulses sent from the water
meter. The controllers can be operated as stand-alone units or connected to a central
computer.
(iii) Normally closed hydraulic valve: a corrosion-resistant valve that controls the flow
of the fertilizer solution into the irrigation system. The valve should be of the normally
closed type in order to cut-off the fertilizer solution flow instantly if the control tube
gets damaged.
Avoiding Corrosion Damage
Most fertilizer solutions are corrosive and may seriously damage metallic
components. Those accessories that are exposed to the injected solution should be
made of corrosion-resistant materials. Furthermore, the injection device and the
irrigation system should be thoroughly flushed after each fertilizer injection.
Backflow Prevention
Whenever the irrigation network is connected to a potable water supply, strict
precautions should be taken to avoid backflow of irrigation water containing fertilizers
into the potable water network. Backflow occurs when the water supply fails. There

73. DRIP IRRIGATION
62
are two principal methods of preventing backflow caused by back-siphonage or back-
pressure.
Back-siphonage occurs when low pressure in the supply line is created by an
excessive hydraulic gradient in undersized pipes in the supply line; a break in the
supply line; pump or power failure.
Back-pressure occurs when the pressure in the irrigation system is higher than in the
water supply pipeline. This happens when booster pumps are used for irrigation or
when the irrigated area lies topographically higher than the domestic supply source.
Physically isolating the potable water network from the irrigation system can prevent
backflow. Some backflow preventers protect against back-siphonage only. Others
protect against both back-siphonage and back-pressure. For public safety, in many
cases a double check valve assembly is required. In other cases a reduced pressure
back-flow check valve is sufficient.
An atmospheric vacuum breaker installed beyond the last valve, allows air to enter
downstream when pressure falls. A pressure vacuum breaker has an atmospheric
vent valve that is internally loaded by a spring. This valve is not suitable for fertigation
systems operated by an external source of energy. Vacuum breakers are effective
against back-siphonage only and cannot be used to prevent back-pressure.
A double check valve assembly has two check valves in tandem, loaded by a spring
or weight and installed as a unit between two valves that when closed allow the
maintenance of the units. The device is effective against backflow caused by back-
pressure or back-siphonage. It is installed upstream of the injection system.
A reduced pressure backflow preventer consists of two internally loaded check
valves, separated by a reduced pressure zone - a chamber between both check
valves with a third valve that opens when pressure downstream is greater than the
pressure upstream – so that water is released to the atmosphere and does not flow
backwards.
In this reduced pressure zone the pressure is normally lower than the pressure at the
inlet and higher than the pressure at the outlet. Whenever the outlet pressure level
approaches the inlet pressure level, both valves close and backflow is prevented.
Fig. 78. Check valve Fig. 79. Tandem backflow preventer - exploded

74. DRIP IRRIGATION
63
Installation of Backflow
Preventers
The backflow preventer
should be installed
upstream, before the
fertilizer injection system.
It should be accessible to
inspection and at least 30 cm above ground.
Fig. 81. Installed backflow preventer
Fig. 80. Tandem backflow preventer

75. DRIP IRRIGATION
64
Chapter 11. WATER QUALITY
Irrigation water quality is defined by its physical, chemical and biological
characteristics. The narrow water passageways in drippers are particularly sensitive
to water quality. On the other hand, due to the frequent applications of water that
dilute salt concentration in the active root-zone, many crop species can tolerate
higher irrigation-water and soil-solution salinity within drip irrigation than in other
irrigation technologies.
Physical quality parameters
Suspended solid mineral particles, organic matter and live zooplankton content.
Chemical quality parameters
Nutrition elements, precipitate-forming ions, salt content and pH level.
Causes of Emitter Clogging
Emitter clogging is caused by particulate matter; biological living organisms their
excretions and their decomposed debris; chemical precipitates and the combined
action of these factors in irrigation water. Poor system design and management
increase the risk of dripper clogging.
Particulate Matter
Emitters can be clogged by particles of sand, limestone or other debris that are too
large to pass through the narrow water passageways. Clogging can also occur when
small particles stick together to form larger aggregates. Even tiny particles such as
suspended clay, which would not cause problems as discrete particles, can initiate
clogging if they flocculate to form larger aggregates.
Biological Substances
Emitters are susceptible to clogging by large particles of organic materials that block
the water passageways if they are not removed by filtering, decomposition or
sedimentation. Clogging can be caused by secretions from microscopic organisms
such as algae and bacteria. Many types of algae are small enough to pass through
filters and emitter passageways as discrete particles, but may flocculate in pipelines
to form aggregates large enough to clog the emitters. Bacteria are small enough not
to cause clogging; however, they can precipitate compounds of iron, sulfur and other
elements that clog emitters. Some bacteria secrete slime that acts as an adhesive
platform for the buildup of clay, algae and other small particle aggregates.
Iron and sulfur bacterial slime is a common problem. Iron-precipitating bacteria grow
in the presence of dissolved ferrous iron in irrigation water. These bacteria attach to
the surface area of suspended soil particles and oxidize the dissolved iron. The
oxidized iron precipitates as insoluble ferric iron. In this process, a slime called ochre
is created, which combines with other substances in pipelines and clogs the emitters.
Specific bacteria that oxidize hydrogen sulfide and convert it to insoluble elemental
sulfur create sulfur slime. This slime, which is a white or yellow stringy deposit, is
formed by oxidation of hydrogen sulfide that is present mainly in shallow wells. The
slime clogs emitters either directly or by acting as an adhesive agent for other small
particles.

76. DRIP IRRIGATION
65
Chemical Precipitates
Chemical clogging of emitters frequently results from precipitation of one or more of
the following minerals: calcium, iron, magnesium and manganese. These minerals
may precipitate from solution and form scales that partially or fully clog emitters.
Precipitation can be triggered by changes in pH, temperature, pressure and reaction
with ions injected into the irrigation water by fertigation, as well as from exposure to
atmospheric oxygen.
Table 16. Relative clogging potential of drip irrigation systems by contaminants in water
Water characteristic Minor Moderate Severe
Suspended solids (ppm) <50 50-100 >100
pH <7.0 7.0-8.0 >8.0
Total dissolved solids (ppm) <500 500-2000 >2000
Manganese (ppm) <0.1 0.1-1.5 >1.5
Iron (ppm) <0.2 0.2-1.5 >1.5
Hydrogen sulfide (ppm) <0.2 0.2-2.0 >2.0
Bacteria population (per ml) <10,000 10,000-50,000 >50,000
After Blaine Hanson. 1997
Determination of Water Quality
An accurate determination of water quality is essential before selecting the filtration
system.
Physical Properties
Dedicated instrumentation has been developed for estimating the "dirt load" in the
water. A tiny hydro-cyclone sand separator is connected to the supply system in
order to measure soil-particle content in water. The amount of accumulated soil
particles in the separation cone indicates the degree of soil content in the water.
A more sophisticated device is the Clogging Potential Meter developed by the Israeli
Water Works Association. This device measures the time required to create a head
loss of 3 m. (0.3 bar) due to the accumulation of particles on its screen while
maintaining a constant flow of water. The time as measured is a comparative index –
Clogging Potential Time – that can be used as an indicator of filtration requirements.
Chemical Properties
The chemical nature of water can be analyzed in a chemical laboratory or with field
test kits. It is particularly important to determine the residual chlorine for efficient
chlorinating.
Salt content can be expressed directly as Total Dissolved Solids (TDS) in mg/l or
indirectly by measuring the Electrical Conductivity (EC). An approximate conversion
from EC into TDS is made with the formula:
TDS (mg/l) ≅≅≅≅ EC (dS/m) X 640
The EC units are deciSiemens/meter (dS/m). TDS units are milligrams/liter (mg/l).
Water Hardness
Water containing substantial concentrations of Ca++
, Mg++
and Fe++
is regarded as
“hard water”. Hard water is prone to the precipitation of their carbonates as salts of
low-solubility in the irrigation system that may clog drippers and filtering systems.

77. DRIP IRRIGATION
66
Water “hardness” is expressed as calcium carbonate concentration equivalent in mg/l
units. Hardness is calculated by measuring the concentrations of the above
mentioned cations, summing up their concentrations expressed in meq/l and
multiplying by 50 (the equivalent weight of calcium carbonate). There are additional
units of hardness, such as British, German or French degrees of hardness.
The most prevalent precipitate from hard water is calcium carbonate. However when
fertigating with fertilizers that contain phosphorous and sulfur, calcium phosphate and
calcium sulfate (gypsum) may also precipitate.
Water hardness is defined by three parameters:
Total hardness: the sum of the calcium, magnesium and bi-valent iron, expressed as
calcium carbonate equivalent in mg/l units
Transient hardness in mg/l units: the bi-carbonate (HCO3
-
) meq/l X 50.
Permanent hardness = total hardness minus the transient hardness.
When water containing calcium bi-carbonate [Ca(HCO3)2] is heated, the following
chemical reaction occurs: Ca(HCO3)2 → CaCO3 ↓ + H2O + CO2↑
Soluble calcium bi-carbonate loses hydrogen and precipitates as calcium carbonate.
Similar reactions occur also with magnesium bi-carbonate.
Calcium carbonate deposits in the drip laterals, inside the drippers and on the filtering
elements. Calcium carbonate sediments may also be created when fertilizers with
alkaline reaction are injected into irrigation water containing a high concentration of
calcium and bi-carbonate. The chemical reaction is:
Ca++
+ HCO3
-
+ OH-
→ CaCO3 ↓ + H2O
Transient hardness can be neutralized by adding acid to either the nutrient solution
or the irrigation water. The neutralization reaction occurs as follows:
Ca(HCO3)2 + H+
→ Ca++
+ H2O + CO2↑
In this process the bi-carbonate ion is decomposed and CO2 is released to the
atmosphere. Attention has to be taken to leave 1 meq/l (61 mg/l) of bi-carbonate in
the water, otherwise the buffer system of the water is impaired and the pH level may
rapidly drop below 4.5 and damage the root system. One meq/l of bi-carbonate in the
water maintains a pH of 6, which is favorable for most agricultural crops. By the
neutralization process, transient hardness is eliminated. However, the permanent
hardness is increased by the same degree. The total hardness remains constant.
Total hardness can be calculated from measured concentrations of calcium and
magnesium cations with the formula:
Total hardness = 2.5 [Ca] + 4.1 [Mg].
Where,
Total hardness is expressed in mg/l as CaCO3.
Ca = calcium concentration (mg/l).
Mg = magnesium concentration (mg/l).
Example:
Total hardness of a water sample that contains 120 mg/l Ca and 45 mg/l Mg.
Total hardness = 2.5 x 120 + 4.1 x 40 = 464 mg/l as calcium carbonate

78. DRIP IRRIGATION
67
Chloride
The chloride anion Cl-
is one of the most detrimental ions when its concentration in
irrigation water is above 150 mg/l, for sensitive crops, and up to 400 mg/l for tolerant
crops. Over 400 mg/l, the water is regarded as brackish, which decreases the yields
of most agricultural crops.
Sodium
High sodium concentrations in irrigation water have a destructive effect on soil
structure as it disperses soil aggregates. Calcium and magnesium cations in the
cation exchange complex moderate the destructive capacity of sodium. Hence, the
destructive nature is determined by the Exchangeable Sodium Percentage (ESP) -
the ratio between Sodium and the sum of the four cation species: Ca++
, Mg++
, Na+
,
K+
.
ESP = % [Na]/([Ca]+[Mg]+[Na]+[K]) in meq/l units
There is a similar relation: SAR – Sodium Absorption Ratio.
meq/l
2
Mg][Ca
[Na]
SAR
+
=
ESP and SAR numerical values are close but not the same. When the value is below
4, agricultural crops are not damaged. In the range between 4 and 8, moderatly
tolerant species are grown, and above 8 only tolerant crops can be profitably grown.
Electrical Conductivity (EC)
Crop sensitivity to total dissolved salts expressed in EC values was defined by Maas
& Hoffman by two parameters: the threshold level above which the yield decreases,
and the slope (%) of yield decrease for increase of one dS/m unit.
The data in table 17 was
derived from experimental
work with diverse irrigation
technologies but not with drip
irrigation. Later it was found
that salinity has a lower impact
on yield with drip irrigation
than depicted in the table.
Many drip-irrigated crops can
tolerate higher salinity with
smaller impact on yield.
The explanation for this
phenomenon is that when the
same volume of water that is
applied over the full-area by conventional irrigation technologies is applies with drip
irrigation, in a smaller wetted volume, the salt is leached more effectively, because of
the relatively high amount of water per volume unit. The frequent wetting events
maintain the EC of the soil solution closer to that of the irrigation water.
Table 17. Threshold and slope of salinity impact on yield
Crop Threshold
dS/m
Slope -
%/dS/m
Bean 1.0 19.0
Corn 1.7 12.0
Soybean 5.0 20.0
Red beet 4.0 9.0
Strawberry 1.0 33.0
Eggplant 1.1 6.9
Pepper 1.5 14.0
Potato 1.7 12.0
Cucumber 2.5 13.0
Tomato 2.5 9.9

79. DRIP IRRIGATION
68
The drawing below demonstrates the variance in salt concentration and the leaching
efficiency of relatively small volume of water applied by drip irrigation.
Fig. 82. Cl- distribution below and between drippers (in
ppm)
Fig. 83. Salt level in relation to
distance from dripper*
Adapted from Hoffman et al. 1980 Adapted from Bresler, 1975
The salt concentration values in Fig. 83. are relative according to the formula (Cfin – C0 )/Cini , when:
Cini = Initial salt concentration in soil solution.
C0 – Salt concentration in irrigation water.
Cfin = Salt concentration in soil solution after application of 12 l water from the dripper.
The Salinity Laboratory in
Riverside, California published
a nomogram in which salinity
and alkalinity hazards to crops
are shown as a function of the
total salt level, expressed as
EC values in the irrigation
water, and the sodium level,
expressed as SAR values,
also in the irrigation water.
This nomogram is extensively
used worldwide, but it does not
relate to the different response
of crops irrigated by drip
irrigation, which can tolerate
higher concentrations of salt.
Sodium affects soil structure
and in this aspect, drip
irrigation has a lower impact
on damage elimination.
Boron
A small amount of boron is
essential for plant growth,
however, a concentration only
Fig. 84. Water quality for irrigation Adapted from US salinity lab guide

80. DRIP IRRIGATION
69
slightly above the optimum in the soil solution is toxic to plants. Some plants are
more sensitive to boron excess than others.
Iron and Manganese
As mentioned before, iron is another cause of precipitates that can clog emitters. Iron
is often dissolved in groundwater as ferrous bi-carbonate. When exposed to air, the
iron oxidizes and precipitates.
Manganese is sometimes also present in irrigation water, but at lower concentrations.
Biochemical Oxygen Demand (BOD)
Organic matter in the water is decomposed by microorganisms that consume oxygen
in this process. The amount of oxygen consumed by these organisms in breaking
down the waste is known as the Biochemical Oxygen Demand or BOD. BOD is a
good indicator for dripper clogging hazard by organic matter contained in the water.
A BOD test measures the amount of oxygen consumed by organisms along a
specified period of time (usually 5 days at 20o
C). The rate of oxygen consumption is
affected by a number of variables: temperature, pH, the presence of certain species
of microorganisms, and the type of organic and inorganic materials in the water. BOD
directly reflects the amount of dissolved oxygen in the water. The greater the BOD,
the higher the organic material content and its clogging potential.
BOD analysis requires taking two samples simultaneously at each site. One sample
is tested immediately for dissolved oxygen content, and the second is incubated in
the dark at 20o
C for 5 days and then tested for the remaining amount of dissolved
oxygen. The difference in oxygen levels between the first test and the second test, in
milligrams per liter (mg/l), is the BOD value. This represents the amount of oxygen
required by microorganisms to break down the organic matter present in the sample
bottle during the incubation period. Because of the 5-day incubation, the tests are
conducted in a laboratory. An innovative procedure that shortened the BOD analysis
to 24 hours was developed and approved by the American Association of Official
Agricultural Chemists (AOAC).
Complementary Water Treatments
In order to prevent clogging of drip irrigation systems, complementary chemical
treatments should be performed on irrigation water, In addition to filtration. Oxidation
and acidification are the most prevalent complementary treatments. Oxidation is
used for the decomposition of organic matter and the prevention of slime formation
by sulfur and iron bacteria, as well as for the elimination of pathogens infestation.
Chlorination
The common oxidizing agent is chlorine. Chlorine can be added to the water as solid
tablets containing 90% chlorine, as liquid sodium hypochlorite (NaOCI) containing
10% chlorine or as gaseous chlorine. The gaseous form is cheap and efficient but is
hazardous in application. When ferrous iron is present in the water, one ppm (part
per million) of chlorine is required per each ppm of iron to kill the iron bacteria and
precipitate the iron from the water. When hydrogen sulfide is present, 9 ppm of
chlorine are needed per each ppm of sulfur to kill the sulfur bacteria, prevent slime
growth and precipitate the sulfur. The precipitates have to be retained by the filtration
system in order to prevent the clogging of the emitters by these particles.

81. DRIP IRRIGATION
70
The main chlorinating agent is liquid sodium hypochlorite. When sodium hypochlorite
is injected into the irrigation water it dissociates into hypochlorous acid and sodium
hydroxide:
NaOCl + H2O → HOCl + NaOH
Equilibrium between the hypochlorous acid HOCl and the hypochlorite ion OCL-
is
maintained in the water:
HOCl ⇆⇆⇆⇆ H+
+ OCl -
.
The hypochlorous acid is 80 times more potent than the hypochlorite ion as an
oxidizing agent.
Effective chlorinating decomposes organic material and blocks the development of
algae and plankton present in the laterals and the emitters. 1 - 2 ppm of residual
chlorine detected at the distal ends of the laterals guarantee adequate chlorination.
To maintain these residual levels, chlorine concentrations at the point of injection
should be in the range of 3 – 15 ppm, depending on the load of impurities and the
duration of injection. Levels higher than 15 ppm are not recommended since they can
harm the diaphragms in pressure-compensated drippers and hydraulic valves. Since
the injected chlorine concentrations are very low, the use of metering pumps is
preferred. When applied in extremely small amount, the chlorine should be diluted to
facilitate precise and even application by the pump.
Acidification
Acidification of water is required when "hard" water containing a high concentration of
bi-carbonates is used for irrigation. The common acidifying agents are sulfuric, nitric
and phosphoric acids. Chlorination of acidified water is considerably more effective
than chlorination of alkaline water, and reduces the chlorine requirement. As
mentioned before, after injecting chlorine into the irrigation water, equilibrium is
created between the active form HOCl and the less active form OCl-
:
HOCl ⇆ H+
+ OCl-
. At low pH values, the active form percentage is higher: 90% at
pH = 6.5; 50% at pH = 7.5 and only 20% at pH = 8.0.
It is highly recommended to implement the chemical treatments upstream from the
filtration system, in order to reduce the load of impurities and trap the decomposed
material in the filters. The narrower the water passages in the emitters, the greater
the requirement for chemical treatments. Acidification should be performed before
chlorination. Mixing both chemical agents of the two processes together results in a
dangerous chemical reaction.
Acid is injected to fulfill two objectives. For the continuous neutralization of the
transient hardness, the concentration of acid in the irrigation water is calculated
according to the bi-carbonate concentration. One meq/l (61 mg/) of bi-carbonate
should be left in the acidified water.
The second objective is to remove calcium carbonate precipitates. For this purpose,
the final concentration of 33 % hydrochloric acid, 60% nitric acid and 85% phosphoric
acid in the irrigation water should be 0.6% – 0.8%. For moderate clogging, an
application time of 10 minutes is recommended, and for severe cases – 20 minutes.
Acid can be applied with regular fertigation equipment or by a dedicated metering
pump.

82. DRIP IRRIGATION
71
Chapter 12. MONITORING AND CONTROL
There are different levels of water and fertilizer management and control for drip
irrigation systems.
At the lowest level, the decisions on water and fertilizer application are based on
personal experience, guessing and intuition, without performing actual
measurements.
More advanced management is based on soil testing with the “feel and see” method.
At the third level, irrigation and fertilization are based on general practice and
recommendations with a preplanned schedule for the irrigation season.
At the fourth level, soil moisture and nutrient content are monitored and water and
nutrients are replenished to desired thresholds.
The tensiometer is the simplest and most
valuable aid for monitoring the performance
of drip irrigation systems. In on-surface drip
irrigation, two units are installed at each
control point. The ceramic tip of one
tensiometer is installed within in the upper
layer, 15 – 30 cm deep, in the active
aerated root-zone. This tensiometer is used
for taking decision about the irrigation
timing. The second tensiometer is inserted
into the lower limit of the active root zone or
the desired wetting depth. This tensiometer
indicates, 12 – 24 hours after water
application, whether the amount of water did
indeed replenish the water in the entire root-
zone.
The chemical composition of the soil
solution can also be monitored using a soil-
moisture extractor – a modified tensiometer.
The soil solution is extracted by exerting
suction with the aid of a syringe.
A more recent soil-moisture monitoring
technology is based on measuring soil
capacitance between electrodes. The
capacitance increases with the increase of
soil moisture.
In greenhouses, drainage water is collected
from the beds, and analyzed in order to
compare its composition with that of the
irrigation water carrying the injected
nutrients. The difference between the two
solutions indicates whether nutrient supply is adequate or not.
At the fifth level, the aforementioned operations are followed by monitoring crop
nutritional state (tissue analysis) and water status (midday leaf or stem water
Fig. 85. Tensiometers
Fig. 86. Soil moisture capacitance sensor

83. DRIP IRRIGATION
72
tension). Water budgeting depends on soil moisture, the water status of the plant and
prevailing climate.
Phyto-monitoring
At the highest level of management, Soil moisture, ambient temperature and evapo-
transpiration, plant water status, nutrient and salt content in irrigation water, water
and soil reaction are monitored simultaneously. The monitoring instruments are
connected to controllers that are activated according to pre-set programs.
Phyto-monitoring is the comprehensive monitoring of soil, plant and climate
parameters. Large-scale field tests using the phyto-monitoring method and
instrumentation were carried out from the year 1998. Experimental phytomonitoring
systems were installed in apple, plum, grapes, peach, kiwi, mango, citrus, avocado
and persimmon orchards. The
parameters of interest are
environmental factors
(temperature, radiation,
relative humidity); plant factors
(daily trunk, shoot and fruit
growth rates) and soil factors
(moisture content, EC and
pH). Three indicators were
used for analysis: diameter
maximum daily trend (DMT),
daily contraction amplitude
(DCA) and the midday stem
water potential (WP). The
DCA is defined as the
difference between predawn
maximum and daytime
minimum trunk diameters.
Fruit tree's trunk, shoot and
fruit were found to be highly
sensitive to soil water deficit.
This makes them good
indicators for irrigation
scheduling With an optimal
irrigation regime, there is a
good correlation between stem
WP, trunk/shoot DCA and
vapor pressure deficit (VPD).
There is no good correlation
however under deficit irrigation
or wherever nighttime air
relative humidity is low, since
the plants’ water reserves are
not completely replenished at night, resulting in a depression of the predawn
maximum. When low humidity prevails over night, the DCA is calculated with a
potential maximum diameter baseline (PMDB) instead of actual predawn maximum.
The ratio of the modified DCA and VPD (DCA/VPD) is a good indicator of plant water
status, both in properly watered and in deficit irrigated crops.
Fig. 87. Multi-factor simultaneous phytomonitoring

84. DRIP IRRIGATION
73
The DMT is a good indicator of soil water availability because of its close relationship
to predawn water potential.

85. DRIP IRRIGATION
74
Chapter 13. SUBSURFACE DRIP IRRIGATION (SDI)
Drip irrigation was originally conceived as subsurface irrigation. This concept was
abandoned in the early sixties due to root intrusion, emitter clogging, and because it
was impossible to monitor visually the wetting pattern as well as the clogging of
emitters and damage to the buried laterals.
Since then, most of the crucial problems have been solved and subsurface drip
irrigation has gained momentum with diverse combinations of crops and soils.
In subsurface drip irrigation (SDI), drip laterals are buried 10 – 50 cm below the soil
surface.
Advantages
Avoiding Interference with
Farming Activities
Farming operations are free of
the impediments due to the
presence of above-ground
pressurized irrigation systems.
Free movement of agricultural
equipment in the field, such as
spraying and harvesting
machines, is essential. Field
operations result in less soil
compaction, and irrigation
induced soil crusting is reduced significantly.
In annual field crops and vegetables, drip laterals do not need to be laid out and
retrieved every season. Deep burying enables soil tilling whenever necessary.
Protection of the Laterals
Burying the laterals protects them from damage by birds, humans and machinery.
Avoiding of exposure to UV radiation and extreme changes in climate conditions
prolongs the laterals’ life expectancy.
Water Conservation
Water is applied directly in the root zone. Evaporation from the soil surface and runoff
are eliminated. Since upward movement of water is driven by capillary forces against
gravity, its range is limited, and with appropriate management, the soil surface
remains dry. Saturated conditions due to water ponding on the soil surface with on-
surface drip irrigation are also eliminated. A dry soil surface does not allow
germination of annual weeds. This further contributes to water conservation and
downgrades the use of herbicides.
Improved Fertilization Efficiency
Uptake of nutrients, particularly phosphorous, is improved, due to its direct
application into the active root zone.
Decreased Incidence of Moisture-Triggered Diseases
The elimination of soil-surface wetting decreases occurrence of moisture-triggered
leaf and fruit diseases such as Alternaria, Mildew, Botrytis and Pythium.
Fig. 88. Scheme of SDI system

86. DRIP IRRIGATION
75
Flexible Application Regime
Scheduling irrigation independently from other farming operations enables the
optimization of the application regime like the frequent application of small water
amounts when needed in extreme weather events such as heat spells.
Applicable for Advanced Water Saving Irrigation Regimes
Ideal for vineyards and orchards – advanced irrigation methods, such as Regulated
Deficit Irrigation (RDI) and Partial Root-zone Drying (PRD) are feasible (These
technologies are dealt with in the chapter on crop irrigation).
Improved Double-Cropping Opportunities
Crops may be planted with optimum timing since the irrigation system need not to be
removed at harvest and reinstalled prior to planting of the second crop.
Extension of Low-Quality Water Utilization
Wastewater can be used safely without workers or the crop coming in contact with it.
Increased Yield and Improved Quality
High irrigation and fertilization efficiency increases the yield and improves its quality.
Disadvantages
Difficulties in the Monitoring of Water Application
Since water is applied underground, it is difficult to monitor and evaluate the system’s
performance and application uniformity. Impaired uniformity can lead to under-
irrigation, resulting in reduced yield and quality or over-irrigation, resulting in poor soil
aeration and losses of water and nutrients due to deep percolation.
Dripper Clogging and Change of Flow Rate
Within SDI, drippers may be clogged by root intrusion and by soil particles being
sucked into the drippers by the vacuum created in the system when it drains after
water shutdown. In heavy soils, the emitter flow-rate may exceed the soil capability to
redistribute the water in a normal pattern. In such cases, water pressure around the
dripper exceeds atmospheric pressure. The counter-pressure may reduce the emitter
flow-rate.
Incompatibility with Cracking Soils
In cracking soils, water applied from drippers underground may have preferential flow
to depth in the cracks and lost without notice, leaving considerable soil volume dry.
Water “Surfacing”
Water may inadvertently “surface” (directing a part of the emitter flow to the soil
surface), causing undesired wetting of the soil surface. Due to “surfacing” events, fine
soil particles may be carried upward with the water, causing a “chimney effect,” that
creates a preferential flow path. The chimney may be difficult to obliterate
permanently, since a portion of the chimney remains above the drip line even after
tillage.

87. DRIP IRRIGATION
76
Difficulties with the Germination of Annual Crops
Using the SDI system for germination may be impossible in certain circumstances,
depending on installation depth and soil characteristics. In such cases,
supplementary irrigation by sprinklers or lateral move has to be given.
Salt Accumulation in the Soil above the Drippers
Salinity may increase above the drip line, increasing the salinity hazard for emerging
seedlings and small transplants. Leaching of these accumulated salts is problematic.
Limits on Soil Tillage
Tillage operations are limited by the depth at which SDI laterals are buried.
Restricted Root Development
Certain soil conditions restrict the development of root systems with SDI more than
with on-surface drip irrigation. The smaller root-zone may be insufficient to avoid
diurnal crop water stress, even when the root zone is well watered. In such cases,
frequent applications of nutrients may be also required, as the smaller root-zone
quickly becomes depleted of nutrients.
Crop Rotation Difficulties
Since SDI systems are fixed spatially, it may be difficult to grow crops with different
row spacing. Some crops might require exceptionally close drip lines spacing, which
may not be economically viable. Particular care should be taken when planting
annual row-crops, ensuring that crop orientation and spacing are appropriately
matched to the location of the drip lines.
Incompatible Crops
Some crops may not develop properly under SDI in certain soil types and climates.
Peanuts may not peg properly into dry soil. Some tree crops benefit from a larger
wetting volume than is attained with SDI.
High Initial Investment
SDI requires a high initial investment compared with alternative irrigation systems. In
certain circumstances, SDI systems have a shorter life span than other irrigation
systems.
Water Quality Limits
For long-term SDI systems, strict water-quality management is required, due to the
impossibility to identify and flush clogged drippers underground.
Rodent Damage
In certain regions, there is a high population of rodents in the soil that damage the
tubes. In such cases, extermination of these rodents is a prerequisite for SDI
installation.
Expensive Maintenance
Maintenance of SDI systems is more complicated and expensive than that of on-
surface drip systems. Leaks caused by chewing rodents are more difficult to locate
and repair, particularly with deep SDI systems. The drip laterals should be monitored
for root intrusion. Roots of some perennial crops may pinch thin-wall drip tapes,

88. DRIP IRRIGATION
77
reducing or cutting-off water flow. The drip laterals should be flushed periodically to
remove silt and precipitates.
Since there are only few visual indicators of system performance and its application
uniformity, frequent monitoring of the system’s water-meters and pressure gauges is
required to find out whether the system is operating properly.
SDI Design
Design of an efficient SDI system requires careful consideration, since once the
system is installed underground and covered with soil, major modification and repairs
are not economically feasible. When used for irrigating annual crops in rotation,
compromises are required regarding dripper and lateral spacing, as well as the
spacing between rows and plants in the rotating crops.
Spacing
Lateral spacing in heavy soils can be wider than in sandy soils. The common range
of lateral spacing is from 1 m in sandy soil to 2 m in heavy soil. Spacing between
emitters on the lateral depends mainly on the crop’s plant density, and vary from 10
to 100 cm.
Lateral and Dripper Type
The drippers of choice are those that are less sensitive to clogging and root intrusion.
Compensated drippers are less prone to flow-rate decrease by build-up of counter-
pressure around the dripper. Trifluraline (Treflan) impregnated drippers and those
equipped with a flap that closes over the outlet after water shutdown, prevent root
intrusion. Drippers with anti-siphonage capabilities are less prone to suction of soil
particles.
Laterals may be made of thick or thin walled PE tubing. In the past, after installation
of thin-wall tapes, the loosened upper soil layer sometimes dried around the flat tape
after water drain and prevented inflation of the tape in the next irrigation. This
problem has been solved by installation of vacuum breakers and the anti-siphonage
capabilities of the new types of drippers.
Lateral Depth
Deep installation, 50 –
60 cm, below soil
surface, enables
regular soil tillage.
This is common in
crops with deep active
root systems, such as
cotton. Irrigation for
germination should be
applied by other
irrigation systems,
such as mechanized
or hand-move
sprinkler laterals.
Shallow installation, 5
– 15 cm deep, is
Sand Clay
Fig. 89. Wetting pattern in SDI

89. DRIP IRRIGATION
78
practiced with shallow-rooted crops, such as strawberry and potatoes.
The system can be used for germinating when the dripper's spacing along the lateral
is between 10 and 30 cm. Whenever germination irrigations are not required, the
installation depth range is 20 – 45 cm. In sandy soils, installation should be
shallower than in heavy soils, since the capillary water ascent is limited. For perennial
crops, installation can be shallow as there is no interference with soil tillage provided
the soil surface is kept dry.
Recent Developments
During the last two decades, most of the problems that plagued SDI systems and
their maintenance had been solved.
Suctioning of soil particles into the drippers at system shutdown is eliminated by
installing air-relief valves at the highest topographic points, and vacuum breakers on
the laterals.
Root intrusion is eliminated by treatment with the herbicide Trifluraline (Treflan).
This herbicide, when applied through the drip system, sterilizes the soil in the vicinity
of the dripper, in a radius of some 2 – 3 cm around the water outlet. The herbicide
does not kill the roots, however it stops their elongation. It remains active for 3 – 6
months after application. One kg/ha/season, divided into 2 – 4 applications along the
irrigation season, eliminates root intrusion into the drippers.
Some manufacturers have developed Treflan-impregnated drippers that continuously
release a small amount of Treflan. This technology is based on the principle of long-
term controlled-release by means of a Polymeric Carrier Delivery (PCD) system. The
PCD system is the chemical’s reservoir, protecting it from degradation. The bioactive
chemical is released slowly to the soil next to the dripper. The declared life-span of
the impregnated herbicide is 10 – 20 years. As mentioned before, "Netafim" offers
disc filters in which the disc stack is impregnated with Treflan. The anti-intrusion life-
span of the discs is 2 – 3 years.
Another technical innovation of SDI installations is a
flush-line manifold connected to the lateral's distal
ends that is used for routine flushing of the drip
system. Occasionally, the flush-line is used as an
additional distributing line that allows the installation
of longer laterals that are supplied with water from
both ends of the lateral. When flushing is required,
the water supply to the flush line is closed and the
drainage valves are opened.
Machinery for mechanized installation of SDI
systems has been developed. These machines
facilitate fast and relatively cheap installation. After
burying the laterals in the soil, the system should be
tested under pressure. Leakages and collapse of
laterals are easily identified and can be repaired
with minimal disturbance.
Fig. 90. Burying SDI lateral

90. DRIP IRRIGATION
79
Fig. 91. Three-shank SDI lateral burying machine

91. DRIP IRRIGATION
80
Chapter 14. FAMILY DRIP IRRIGATION
In developing countries, irrigation is practiced on a wide-scale for growing fruit and
vegetables in family-owned gardens, some of which are not larger than 20 – 500 m2
.
These gardens are mostly furrow-irrigated with water drawn from shallow wells,
rivers, lakes and reservoirs; either by hand, animals or by small motor-driven pumps.
Experimentally, productivity has been impressively improved by replacing furrow
irrigation with drip irrigation. Conventional drip technology is not suitable for these
small gardens. It is expensive and out of the reach of small producers.
Low-pressure drip irrigation systems for these small holders were developed by Mr.
Chapin of "Watermatics", USA, Mr. Rosenberg of "Ein Tal" and by "Netafim", Israel.
Mr. Chapin invented the Bucket-kit technique. The kit is composed of an ordinary
bucket, a filter, delivery tubes and two 15-m long drip laterals. The bucket is hung
one meter above ground, and the two laterals deliver water by gravity to the
vegetable garden. Two 40-l buckets of water meet the daily consumption of a family
garden. The bucket-kits cost six dollars each to non-profit organizations. They are
distributed by NGOs in over 100 countries.
A larger capacity bucket kit was developed later on. The Super Bucket Kit provides
drip irrigation for 10 rows, 10 meters long each, covering 100 m2
. This area can be
watered from a 250-l container filled once a day.
Fig. 92. Bucket kit Fig. 93. Drum kit
A modification of the bucket kit technology was developed by IDE: A five-dollar
starter kit irrigates 25 m2
of vegetables. The same system with twice as many laterals
irrigates 50 m2
. A $25 drum kit utilizes a 200 - 300-l drum tank for the irrigation of 125
m2
and a simplified irrigation system for irrigating 0.4 ha. was also developed
Shift able drip systems reduce capital cost by using more labor. Each lateral is
capable of irrigating up to ten rows. Water drips out of baffled holes or curled micro-
tubes, instead of expensive emitters.
Larger low-cost drip systems for irrigation of 1000 to 10,000 m2
for crops like cotton
cost $625/ha. One lateral can irrigate four rows with attached micro-tubes.

92. DRIP IRRIGATION
81
"Netafim International" developed
two models of gravity-pressurized,
drip systems for irrigating 400 m2
of
vegetables. Both types include a
tank, filter, valves, main line,
manifold and laterals. The first
model has a 50 m main line and fifty
7.5 m lateral tubes. It is suitable for
greenhouse or low-tunnel cropping.
The second model has a 9 m main
line and nine 20 m lateral tubes on
both sides. The tubes are heavy-
duty, durable, small-diameter of 5–9
mm OD. The system costs $150 per
1,000 m2
.
Complementary to these systems, a
human-powered treadle pump that
costs only $30 (compared to $300
for a diesel pump) was developed.
There are two treadle pump
models: one is powered by walking
on two bamboo treadles, while the
other is comprised of steel treadles
connected to concrete platforms
and tubes. The treadles activate
two steel pistons that may be
manufactured in any village
workshop
.
Fig. 94. "Netafim" Family Drip System (FDS)
Fig. 95. Components of Family Drip System (FDS)
Fig. 96. Treadle pump

93. DRIP IRRIGATION
82
Chapter 15. WATER DISTRIBUTION UNIFORMITY
One of the parameters for the evaluation of irrigation excellence is the Irrigation
Efficiency (IE), which is defined as:
waterappliedtotal
usedlybeneficialwater
IE =
Water beneficially used includes replenishment of evapo-transpiration consumption,
frost protection, pesticide and fertilizer applications, salt leaching, and crop cooling.
Drip irrigation facilitates the application of the same volume of water to every single
plant in the irrigated plot. This requires the suitable spacing between laterals and
drippers as well as the appropriate pressure regime.
Application uniformity can be expressed with various indices. A uniformity of 100%
means that each point within the plot receives exactly the same amount of irrigation
water. When uniformity is low, some sections of the plot receive less water than
others. In order that those areas that obtain less water will receive a sufficient
amount of water, additional water has to be applied to the plot as a whole.
Application uniformity is particularly important with drip irrigation systems, due to the
cumulative nature of non-uniformity.
A common index of application uniformity is Distribution Uniformity (DU). To calculate
this value, the flow-rate of a representative sample (40 - 100 emitters randomly
selected in different sections of the irrigated plot) is measured.
Where: Q25% is the average flow rate of 25% of the emitters with the lowest flow rate,
and Qn is the average flow rate of all the sampled emitters. DU values above 87%
indicate excellent distribution uniformity; 75% - 87% - good uniformity; 62% - 75%
acceptable and below 62% the uniformity is unacceptable.
Variation in the flow rate depends on the pressure regime, partial emitter clogging
and the manufacturing variance of the drippers.
In addition to variation of the flow-rate between emitters due to pressure differences,
flow rate variation also occurs because of manufacturing variation. No two emitters
can be identically manufactured; there will be some variation among emitters. The
flow rate uniformity of new drippers is evaluated with the Manufacturing Coefficient of
Variation (Cvm).
The flow-rate variation due to manufacturing variance is determined statistically.
Randomly-selected emitter samples or a lateral section are tested under constant
pressure. The Cvm is defined as the standard deviation divided by the average flow
rate of a sample of emitters. It is expressed as a decimal fraction or percentage. 0.01
= 1%. According to the formula:
Cvm = Sdm/Xm (as decimal fraction). Multiplication by 100 gives the % expression.
Where: Cvm = manufacturing coefficient of variation,
Sdm = standard deviation,
Xm = mean flow rate.
A Cvm of 0.1 (10%) means, assuming a normal distribution (a “bell shaped” curve),
where 68 %of all dripper flow rates are plus or minus within 10% of the mean flow

94. DRIP IRRIGATION
83
rate. The emitter's design, material used in its production, and manufacturing
precision determines the variation for any particular emitter type. A Cvm of 0.05 or
less is considered excellent, 0.05 - 0.10 is good, 0.10 - 0.15 is marginal, and higher
than 0.15 is poor. With the recent improvements in manufacturing tolerances, most
emitters have Cvm < 0.10. Pressure compensating drippers have a somewhat greater
Cvm than non-compensating labyrinth path emitters.
Another expression used for the evaluation and design of drip systems is the emitter
flow variation in the lateral. This compares maximum and minimum emitter flow rates.
qvar=(qmax - qmin)/qmax
or
qvar= 1-(qmin/qmax)
Where qmax is the maximum emitter flow rate, qmin is the minimum emitter flow rate,
and qvar is the emitter flow rate variation. It is assumed that the manufacturer's emitter
flow variation follows a normal distribution so that the mean value plus two standard
deviations is considered as the maximum flow rate and the mean value minus two
standard deviations is considered as the minimum emitter flow rate. This range
covers over 95% of the emitter flow-rates measured in the tests.
Relating test results to the manufacturers Cvm indicates that with a manufacturing
Cvm of 0.05 = 5%, the difference between maximum and minimum flow rates may
reach 15%.
Emission Uniformity (EU) combines variation due to emitter-manufacturer variance
and variation due to pressure. This is a design parameter. In new installations or
when there is no emitter clogging, EU (design) is approximately equal to DU.
EU is given as:
EU = [(1 -1.27(Cvm)) X (Qmin/Qavg) X100]
Where,
Cvm = manufacturer’s coefficient of variation
Qmin = minimum emitter pressure dependent discharge.
Qavg = mean emitter pressure dependent discharge.
The actual uniformity of discharge from drippers decreases along time due to partial
clogging of the water passageways, deformation of drippers and compensating
membranes, as well as mechanical damage to laterals. Routine periodical inspection
and corrective measures are requested to guarantee uniform water distribution within
an irrigated plot for the long run.

95. DRIP IRRIGATION
84
Chapter 16. DRIP IRRIGATION OF CROPS
Drip irrigation is suitable for most
agricultural crops as well as for many
gardening and landscaping applications.
Use of detached media for hydroponics
led to the expansion of drip irrigation to
the protected cropping industry.
Impressive water saving and yield
increase have been achieved all over the
world after converting from traditional
surface irrigation to drip irrigation. Table
17 presents data from the state of
Maharashtra in India. The figures relate
to the third year after conversion from
surface to drip irrigation.
Crops respond in different ways to drip
irrigation. Perennial crops growers benefit
from the localized water application that
reduces interference of irrigation with
other farming activities, as well as from
the frequent application of water and
nutrients and the decreased hazard of
salinity damage in the root zone.
Annual crops benefit from substantial
water saving during the early stages of
crop development as well as from the
frequent application of water and
nutrients. Another benefit is the
decreased incidence of plant diseases
enhanced by high ambient humidity.
Drip Irrigation in Orchards
The introduction of drip irrigation to
orchards, significantly changed the water
and nutrient application regime. Prior to
drip irrigation, the irrigation policy in
orchards was to stretch the intervals
between irrigations as much as possible.
The prevalent concept was that
stretched intervals induce the
development of a deep root-system and
the trees would better withstand water
stress without damage to yield and fruit
quality. Intervals of 20-30 days between irrigations were common and large volume
of water had been applied at each application.
After the introduction of drip irrigation, it was found that most fruit trees respond
positively to frequent applications of small amounts of water. Root exposure
Table 18. Yield increase and water savings in
conversion from surface to drip irrigation
Crop Yield
increase
%
Water
saving
%
Banana 52 45
Grapes 23 48
Sweet lime 50 61
Pomegranate 98 45
Sugarcane 33 56
Tomato 50 39
Watermelon 88 36
Cotton 27 53
Cabbage 2 60
Papaya 75 68
Radish 2 77
Beet 7 79
Chillies 44 62
Sweet potato 39 60
After Desai & Sudhakar, 1993
Fig. 97. Apple root system in well aerated soil
Fig. 98. Apple root system in compacted soil
Adapted from Tamasi 1986

96. DRIP IRRIGATION
85
revealed that contradicting the traditional perception, in certain soil conditions, like
shallow topsoil, stratified soil, poor soil aeration and high water tables the crop
benefits from frequent irrigations because of the shallow root system is shallow.
There are different types of
drippers' layout in orchards. For
heavy and medium textured
soils, one drip lateral along the
row is usually sufficient. On
sandy and shallow soils, two
laterals, 20 – 60 cm apart on
each side of the row, perform
better. There are additional
layouts such as loops and half
circles around the trunk, star
layout, meander, “snake” and
fishbone layouts as shown in the
figure.
The most pronounced water
savings in orchards with drip
irrigation is during the early
years, prior to fruit bearing. Some
types of laterals allow for opening
only the water emitters adjacent to the tree in the early years of the orchard
establishment. The plugged outlets between the trees are gradually unplugged,
matched to the expansion of the root system.
Some fruit crops particularly benefit
from drip irrigation, while others are
better compatible with spray and micro-
sprinkler irrigation.
The shift from surface to drip irrigation
of bananas led to water savings in the
order of 50% - 70%. One lateral per
row is sufficient.
Drip irrigation and fertigation of table
and wine grapes improved yield and
quality, followed by impressive water
savings. To avoid the damage to on-
surface laterals, it is common to hang
the laterals 30 cm above ground by fastening them with a clip to the lowest wire on
the trellis.
Fig. 101. Dripper layouts in pecan orchard
Fig. 99. Drip irrigation Layouts in orchards
Fig. 100. Drip laterals in vineyard, hung on the trellis wire

97. DRIP IRRIGATION
86
The introduction of mechanized harvesting and pruning machinery triggered the shift
to SDI. Burying the laterals avoids damage by the machinary.
For wide-spaced orchards, such as pecan plantations that are planted 10 by 10 to 15
by 15 m spacing, one lateral per row is mostly insufficient to satisfy the tree's water
requirements. Two laterals per row or loops around the trunks are the recommended
layouts.
When considering implementation of drip irrigation in citrus and other evergreen sub-
tropical crops such as avocado and mango, it should be taken into account that drip
irrigation is not suitable to modify the micro-climate in the plot while sprinkler and
sprayer systems can reduce or avoid the effect of extreme weather conditions, such
as heat spells or frost by decreasing or increasing the ambient temperature.
In deciduous fruits orchards, such as peaches, prunes, apples, pears and vineyards,
drip irrigation facilitates implementation of the innovative RDI and PRD water-saving
regimes.
RDI (Regulated Deficit Irrigation) is based on the fact that some of the phenological
growth stages during the plant’s life cycle are less sensitive to stress due to water
deficit.
For example, fruit growth of peaches is slow during the pit hardening stage that lasts
45 – 60 days. Full deficit replenishment of the transpired water during this period only
slightly affects the final fruit size at harvest and does not reduce yield. Water saving
of up to 20% of the annual application may be obtained. The less insensitive stage of
pears is shorter and water saving of some 10% - 15% of the annual consumption is
common with RDI. Similar results were achieved in prunes, table and wine grapes
and almonds.
Water deficit is deliberately created in wine grapes during the post-set period of berry
development, to restrict vegetative growth. This practice has resulted in significant
improvement of wine quality.
RDI can be applied also with other micro-irrigation methods, such as sprayers and
micro-sprinklers; however water savings will be less significant.
Fig. 102. Typical shoot and fruit growth curves for peach (left) and pear (right)

98. DRIP IRRIGATION
87
PRD (Partial Root-zone
Drying) was developed in
Australia. The concept is to
alternately wet one side of
the root system using two
laterals per row. This allows
maintaining the vines at a
low level of stress, with only
half or slightly more of the
volume of water applied
when wetting the entire root-
zone.
PRD is based on the manipulation of transpiration control mechanisms.
Approximately one half of the root system is maintained in a dry or drying state, while
the remainder of the root-zone is kept wet. For wine grapes, the wetted and dried
sides are alternated in a 10 – 14 days cycle.
PRD saves more water than RDI – up to 40% in wine and table grapes – and further
improves wine quality of certain varieties.
Nutrition Ditches
Another contribution of drip
irrigation to overcome
orchard management
problems due to harsh soil
conditions such as
compactness and alkalinity
is the implementation of drip
irrigation in nutrition ditches.
This technology implies
excavating, one or two
ditches, 30 – 50 cm deep
and 20 cm wide at some
distance from the row of
trees. The sides of the
ditches are padded with a
geo-chemical fabric, in order to protect them from destruction. The ditches are filled
with aggregates of volcanic tuff, pumice, gravel or perlite. A drip lateral is laid over
each ditch. During the irrigation season, water and nutrients are applied in pulses,
several times a day with a regime similar to that of greenhouse irrigation.
The most impressive results were achieved in mango plantations. Yields increased
from 5 – 10 t/ha. to 40 – 50 t/ha. Peaches, nectarines and table grapes also
responded positively but in a lower extent.
Drip Irrigation in Field and Fodder Crops
Drip irrigation does not compete with mechanized irrigation, which is cheaper when
applied to large, rectangular and flat plots of field crops. Drip irrigation is the
recommended technology for small plots, plots of irregular form or where topographic
conditions are particularly harsh.
Fig. 103. Partial Root-zone Drying with two laterals per row
Fig. 104. Mango grown on nutrition ditches (right) vs. control (left)

99. DRIP IRRIGATION
88
SDI is widely used in field-crop irrigation when mechanized irrigation is not
applicable. The required precision in sowing and planting in the same rows every
year is supported by the use of GPS instrumentation on the farm machinery.
For on-surface drip irrigation, drip laterals are laid out at the beginning of the
irrigation season and retrieved pre-harvest to avoid damage to the equipment.
The spacing between rows and
between plants in the row is not the
same for all field crops. Lateral and
dripper spacing should conform to the
crop spacing. Row spacing is modified
for some crops in order to reduce the
number of laterals. For example,
instead of a uniform spacing of 1 m
between rows, the rows are paired at
80 cm with 1.20 m between adjacent
row pairs. This allows for the
installation of one lateral between each
pair, (at 40 cm from each row), instead
of one lateral per row. This layout
decreases total lateral length in the plot
by 50%. With SDI, there are always
dilemmas regarding the spacing and
installation depth of the laterals. For
deep-rooted crops such as cotton
growing on heavy soil, the spacing
between laterals can be twice the spacing between rows, approximately 2 m. This
requires germinating the crop with a separate irrigation system,
such as self-propelled irrigation machines.
For crops with shallow root systems, the
greatest spacing between laterals is 1 m
and installation depth is 30 – 40 cm. This
limits tillage options.
Drip Irrigation of Cotton
Drip irrigation in cotton is applied mainly
on shallow soils, small or irregular plots
and on steep slopes. A substantial part of
drip irrigated cotton employs on-surface
retrievable laterals that are laid out after
planting and collected pre-harvest.
Machinery developed for this technology
enables laying out up to 8 rows at one
pass. SDI systems are used mainly on heavy compacted soils, in order to eliminate
traffic of laying/retrieving machinery on wet soil.
Since cotton is a non-edible crop and is relatively resistant to salinity, vast area of
cotton is irrigated with low-quality reclaimed and brackish water. Reclaimed water
requires the use of high-quality filtration systems.
Fig. 105. Mechanized deployment of drip laterals
From "Naan" brochure
Fig. 106. Cotton root development

100. DRIP IRRIGATION
89
Drip Irrigation of Tomatoes for the Processing Industry
Drip irrigation has many advantages in irrigation of tomatoes for processing. The
capacity to optimize water and nutrient supply according to climatic conditions,
phenological stages, yield potential and planned harvest date, increases yield and
maximizes the fruit’s dry matter and sugar content. Tomatoes for processing are
sown at spacing of 1.5 – 2 m between rows, with one or two laterals per row,
depending on soil texture, depth and stratification,
SDI installation eliminates the annoying task of laterals retrieval under the sprawling
plants. Improved quality was also reported as a result of better nutrient utilization and
elimination of soil-surface wetting.
Drip Irrigation of Potatoes
Drip irrigation of potatoes was
controversial for many years. Growers
argued that drip irrigation triggered the
development of malformed bulbs.
Shallow burying of the lateral, 5 – 15
cm deep with small spacing, 10 – 20
cm between drippers along the lateral,
eliminates this problem by wetting a
continuous strip along the row.
Installing one lateral on each raised bed
is essential for potatoes on sandy and
medium textured soils. When the lateral
is laid on the raised bed, it should be
placed in a shallow groove to maintain
its position on the top and to decrease
runoff along the bed's slope. On heavy soils, the lateral can be laid between two beds
so that the root-zone remains well aerated.
Drip Irrigation of Corn
Corn appears to be one of the most responsive crops to drip irrigation. The capacity
of managing the optimal supply of nutrients contributes to the development of bigger
cobs that increases yield. Laterals are laid one per row or between paired rows,
depending on soil type.
Drip Irrigation of Alfalfa
Alfalfa was one of the last crops that were adapted to drip irrigation. Due to the high
plant density, it was regarded as not justified economically. The use of reclaimed
water for the irrigation of alfalfa obliged the installation of SDI in order to avoid
Fig. 107. Laterals on top of hillocks in potatoes Fig. 108. Lateral between hillocks After Kremmer & Kenig
Fig. 109. Potatoes – one lateral per row Courtesy "Netafim"

101. DRIP IRRIGATION
90
contamination of the crop with pathogens. The deep root system of alfalfa allows for
a spacing of 1 – 1.2 m between laterals, without any decrease in yield.
Drip Irrigation of Vegetables
Most vegetables grown both in the open field and within protecting structures
respond positively to drip irrigation and fertigation. Consumption curves of water and
nutrients were elaborated for many species. Drip irrigation facilitates supply of water
and nutrient following these curves. The predominant technology for open field
culture is on-surface seasonally-retrievable drip irrigation. SDI is seldom installed. In
California, the pioneer of SDI for vegetables, there has been recently return to
traditional drip irrigation with the drip laterals on the soil surface; due to problems
during the germination and emergence of the crops grown with SDI. Yield decrease
in long-term SDI irrigation in some vegetable species had been reported.
Drip Irrigation of Open-Field Tomatoes, Pepper and Eggplants
Drip irrigation of the main species of the Solanaceae family (in addition to the before
mentioned potatoes and tomatoes for processing), has greatly increased worldwide
during the last three decades. Water saving and decrease in fungal disease
occurrence, compared with sprinkler irrigation; improved nutrient supply, compared
with furrow irrigation; and increased yields, convinced farmers to expand the drip
irrigated area of these crops. The prevalent layout is one lateral per row. The soil
type determines the spacing between drippers on the lateral, ranging from 10 cm with
thin-wall tapes and in sandy soils to 50 cm on heavy soils.
Drip Irrigation of Strawberry
Strawberries are usually grown on four-row raised beds with plastic mulch in open
fields. The spacing between the rows is 20 – 30, and between plants in the rows 15 –
30 cm. The common layout is one lateral between each pair of rows and spacing of
10 – 30 cm between drippers along the lateral. The laterals are installed beneath the
plastic mulch in order to decrease incidence of Botrytis, which is enhanced by direct
contact of the berries with wet soil.
Drip Irrigation of Cucumbers, Melons and Watermelons
The wide spacing between rows (1 – 2 m) of crops of the Cucurbitaceae family,
results in enormous water saving during the early growth stages before the foliage
fully covers the soil surface between rows. The common layout of one lateral per row
renders a relatively cheap system.
Drip Irrigation of Celery
Celery is grown on 4 row beds, 1.5 – 2 wide. Laterals are laid in the middle of each
pair of rows. Drippers are spaced 20 – 30 cm apart along the lateral.
Drip Irrigation of Cabbage and Lettuce
Cabbage and lettuce are grown on 4 row beds, 1.5 – 2 m wide. Laterals are laid in
the middle of each row pair with drippers spaced 20 cm along the lateral.
Drip Irrigation of Cauliflower
Cauliflower is grown on a double-row bed, 1.2 -1.8 wide. On heavy and medium
textured soils, the layout is one lateral per bed, in the middle, between the two rows.

102. DRIP IRRIGATION
91
On sandy soils, one lateral per row is the preferred layout. Dripper spacing along the
lateral is 20 – 30 cm.
Drip Irrigation in Protected Crops
Protected crops are grown at diverse levels of environmental protection. The highest
level is a glasshouse structure, with full environmental, irrigation and nutritional
regulation. The second degree of protection consists of plastic covered greenhouses
and walk-in tunnels. The greenhouse sector can be divided into those growing the
crop on the native soil and those using diverse types of detached media. In some of
these structures, full environmental control is also maintained. However, in most of
them, only irrigation and nutrition are automatically controlled. A lower degree of
control is maintained in low tunnels that provide only partial environmental control,
however irrigation and plant nutrition may be fully controlled. The lowest degree of
protection is plastic mulch that covers the soil to preserve water, reduce temperature
fluctuations within the root-zone and eliminate direct contact of the fruit and foliage
with the soil and with the irrigation water.
Fig, 110. Wide-scale drip irrigation in greenhouses Courtesy "Netafim"
Apart from specific circumstances in which the relative humidity within the protected
structure must be increased by spray, fogger or sprinkling emitters, most of the
protected cropping area is irrigated by drip irrigation. For crops grown on native soil,
the drip system layout is similar to that implemented in the open field. The only
difference is that protected crops are grown mostly on coarse textured soils, that may
be imported from an external source if the local native soil is of fine texture. Coarser
soils require narrower spacing between laterals and drippers as well as shorter
intervals between irrigations.
Most of the detached beds have a low water-retention capacity requiring frequent
water applications and denser layout of laterals and drippers. In pot plants, multi-
outlet drippers are used, as well as dedicated drippers such as the arrow dripper.
Many of the detached beds are fully or partially inert materials, therefore complete
fertilization is required, including all the 15 plant nutrition elements. Some of these
elements cannot be mixed together in their concentrated forms, and 2 – 4 separate
fertilizer tanks are required, each with its own injector. More sophisticated systems
employ the mixing tank in which 2 – 4 different nutrient solutions are mixed and

103. DRIP IRRIGATION
92
injected into the irrigation system. In some mixers the nutrient mixture is diluted with
water up to the desirable final nutrient concentration and pumped into the irrigation
system as it.
Environmentally controlled
greenhouses are expensive. Therefore,
in order to maximize income, the
available space is filled to the
maximum: potted plants, propagation
beds, grafts and trays for germinating
transplants are arranged in several
horizontal layers, on separate stories,
one above another. Multi-outlet
drippers are the most economical
irrigation solution for this arrangement.
Greenhouses that recycle drainage
water for reuse in irrigation require a sterilization system like ultra violet (UV)
irradiation; heating the recycled water to high temperature or slow sand filters (SSF).
These means are required to prevent infestation by pests such as fungi, bacteria,
nematodes and viruses that may exist in the recycled drainage water.
All these systems are monitored with and controlled by diverse sensors and
computerized controllers.
Drip Irrigation in Landscaping
Drip irrigation has been extended to the
irrigation of private and public
landscaping. Small-scale private
landscape installations may use
adjustable drippers to facilitate
concurrent irrigation of plants with
different water requirements.
Adjustable drippers are also useful
when water requirements of the plants
change during the irrigation season.
SDI is used extensively on turf and golf
courses as well as in sports facilities such as football fields and tennis courts. Dripper
density in turf grounds is much higher than for agriculture. Spacing of 40 – 50 cm
between laterals is prevalent in sandy turf and sport grounds with coarse aggregates
– volcanic tuff, pumice, gravel and perlite infrastructure.
Drip irrigation provides the optimal solution for roadside irrigation, along pavements
and at interchanges. In addition to substantial saving in irrigation water, it eliminates
the danger to traffic stemming from wet roads and walking lanes.
Frequently, the water supply to gardens is connected to the drinking-water supply
system. This obliges the installation of backflow preventers. In many countries,
installation and management of backflow preventers are enforced by state or local
authority regulations.
Fig. 111. Drip irrigation of potted plants in
greenhouse Courtesy "Netafim"
Fig. 112. Roadside drip irrigation Courtesy "Netafim"

104. DRIP IRRIGATION
93
Chapter 17. BASICS OF DRIP SYSTEM DESIGN
When designing new drip irrigation system, a number of parameters should be taken
into account in order to engineer an optimal and durable system.
The first step should compare the crop water requirements with the available annual
water supply capacity. The system's discharge capacity should be compared to peak
season demand.
The pre-design data can be divided into a number of categories: climate, cropping
technologies, soil properties, topography, water-supply capacity and quality, available
equipment.
Climate and Crop Data
1. Peak season maximum daily evaporation (mm/d). Measured with a class A
pan or calculated from climatic data.
2. Net daily crop water requirement (mm/d) = daily evaporation X crop coefficient
– mm (multiplied by 10 = net daily crop water requirement m3
/ha/d)
3. Gross daily water requirement (mm/d) = Net daily crop water requirement
divided by the application efficiency (expressed as percentage or decimal
fraction)
4. Net daily water requirement per irrigated area (mm/d or m3
/d) = Net daily
requirement X irrigated area (ha.).
5. Gross hourly water requirement = gross daily requirement divided by the
number of water supply hours. Supply hours never exceed 20 hours per day.
The extra hours are set aside for maintenance.
Example:
Max daily evaporation during the irrigation season: 8 mm
Crop coefficient: 0.7 (70%)
The daily irrigated area: 30 ha
Application efficiency: 80%
Available water supply hours per day: 14h
Net daily crop water requirement: 8 mm/d X 0.7 = 5.6 mm/d (56 m3
/ha/d)
Gross daily crop water requirement: 56 m3
/ha/d /80% = 70 m3
/ha/d
Gross daily water requirement per irrigated area: 70 m3
/ha/d X 30 ha = 2100
m3
/d
Hourly water demand: 2100 m3
/d /14 h/d = 150 m3
/h
Cropping Data
1. Crop rotation data
2. Length of growing season
3. Spacing between rows and between plants along the row
4. Depth of root-zone
5. Water and nutrient consumption curves, (required for the design of the
fertigation system)

105. DRIP IRRIGATION
94
Soil Properties
1. Soil depth
2. Soil texture and structure
3. Specific gravity
4. Bulk density
5. Saturation Percentage, Field Capacity, Wilting Point
6. Presence of stratified layers
7. Infiltration rate and hydraulic conductivity data, if available
8. Soil salinity
Topography
Topographic maps
Water Supply Capacity
1. Water source properties (river, dam, pond, well, public/commercial supply)
2. Hours of supply (if by external supplier or limitations in the electricity supply)
3. Maximum hourly flow-rate (discharge)
4. Pressure at supply connection (if by external supplier)
5. Water quality (physical contamination, salinity)
Existing Equipment
Existence of pumping equipment, delivery and distribution pipelines, emitters,
accessories, etc.
Preliminary Considerations
Preliminary considerations include the selection of dripper type and flow-rate and the
recommended working pressure. This has to conform to the crop's spacing and with
soil properties.
The pattern of the wetted soil volume by
a single dripper is an important factor in
these considerations.
The wetting pattern is determined by
the dripper discharge, infiltration rate of
the soil (expressed in mm/h) and its
hydraulic conductivity (expressed as
mm/s). The difficulty with the last two
parameters is that the first decreases
along time during the irrigation and the
second is measured in saturated soil,
while in drip irrigation, there is water
movement also in unsaturated soil.
Models for estimating the wetting pattern were developed by Schwarzman and Zur
(1986) and Shani (1987).
In the first model, the wetted-volume diameter depends on the dripper flow rate.
Fig. 113. Wetted volume in different soil types

106. DRIP IRRIGATION
95
D = K X 1.32z0.35
X q0.33
X Ks
-0.33
When: K = Empirical coefficient (29.2)
D = wetted diameter, m
z = desired wetting depth, m
q = dripper flow rate, l/h
Ks = saturated hydraulic conductivity, mm/s
If the irrigated plot is uniform – one and the same crop at the same phenological
stage – water distribution should be as uniform as possible. For drip-irrigation system
design, the accepted maximum allowed difference in the flow-rate between emitters
in the plot is 10%, namely 5% above and 5% below the average.
Calculation of head losses when water flows in pipes is the primary step in the design
of the system. There are different formulae for calculating head losses. Designers
routinely use tables, nomograms, on-line calculators and dedicated software for
irrigation design.
When designing drip systems, it is recommended to analyze several alternatives,
comparing initial investment cost, labor and energy expenses.
Example
Design of drip system in apple orchard:
Crop Data
Crop: Apple
Variety: Golden Delicious
Area: 10.4 ha.
Spacing 4 X 4 m
Irrigation season: Apr - Oct
Harvest: Sept – Oct
Active root depth: 80 cm
Maximum allowed water
depletion: 40%
Highest crop coefficient: 0.9
Soil data
Texture: Loamy clay
Depth: 1.20 – 1.50 m
Bulk density: 1.4
Field capacity: 32% V/V
Wilting point: 15% V/V
Available water: 17% V/V
Wetted soil volume diameter by a single dripper: 80 cm (on the spot test)
Climatic data
Peak season daily class A pan evaporation: 8 mm
Water supply data
Maximum supply hours: 14 hours a day
Maximum available hourly discharge: 100 m3
/h
EC water: 1.2 dS/m
Chloride content: 150 mg/l
Fig. 114. Apple orchard – 7.68 Ha
.
a

107. DRIP IRRIGATION
96
Calculation of Peak Season Water Demand
8 mm/d X 7.68 ha. = 61.44 mm/d = 614 m3
/d (1 mm = 10 m3
/ha.)
Average hourly demand: 614/14 = 43.9 m3
/h. The demand complies with supply
limits.
The initial examined alternatives are "Netafim" in-line non-compensated 122 dripper
(OD = 12 mm) with flow-rate of 2.1 l/h at 10 m head and 2.6 l/h at 15 m head, spaced
1 m apart on the lateral.
A second alternative is Ram 16 compensated dripper (OD = 16 mm) with flow-rate of
1.2 l/h, spaced 50 cm on the lateral.
Dripper manufacturers publish data about the maximum allowed length for drip
laterals on flat land, keeping drippers' flow-rate variation due to friction in laterals
within 10% (+/- 5% of the average).
Table 19. Manufacturer data about the allowed lateral length in the examined alternatives
"Netafim" In-line drippers Maximum lateral length (m) on leveled ground at 10% flow-rate
variation*
Drippers and laterals are chosen according to the manufacturer’s data. The table
presenting in-line dripper hydraulic data shows that for laterals of Type 122 with
drippers spaced at 1 m., a length of 80 m is marginal. To be on the safe side, it is
recommended to choose the type 162 dripper lateral with a 16 mm OD tube instead
of a 12 mm OD that has the same flow rate as the 122 dripper. The maximum
allowed length of these laterals at 1 m spacing is 133 m instead of 81 m.
The design process includes two phases. In the first phase, head loss is calculated
from the tail to the head of the plot, using average values of head and flow rate. In
the second phase, the design is checked, going from the head to the distal end. At
this stage, the calculation relates to precise actual data.
The map of the plot is divided into sectors and detailed calculations are performed on
each pipe segment. The data have to be registered in the design form. Head losses
in accessories are calculated using the data of equivalent length indicating head
losses in a virtual pipe of the same diameter as that of the accessory. Most
manufacturers provide tables and nomograms of head losses in their products.
Dripper Spacing - mLateral
Type
Ǿ
mm
Flow-rate
l/h 0.30 0.40 0.50 0.60 0.80 1.00 1.25 1.50
121 12** 1.0 47 60 73 84 106 127 150 171
122 2.0 30 38 46 54 68 87 96 111
124 4.0 19 25 31 36 45 54 63 73
161 16*** 1.0 83 104 124 142 176 207 242 274
170 1.5 63 79 95 108 164 158 185 210
162 2.0 53 66 79 91 112 133 156 177
164 4.0 35 44 52 60 75 88 103 117
168 8.0 22 27 33 37 47 55 65 73
* Distal pressure=10 m. ** O.D.=12.5 mm / I.D.=10.1 mm. *** O.D.=15.8 mm / I.D.=13.2 mm.

108. DRIP IRRIGATION
97
Table 20. Allowed lateral length of Ram 16 PC drippers
Ram 16 PC (OD 16 mm), Flow-rate 2.3 l/h, allowed lateral length (m), distal head = 10 m
Dripper spacing - mHead in
Inlet (m) 0.15 0.20 0.25 0.30 0.40 0.50 0.60 0.80 1.00 1.2
15 38 50 61 72 93 113 132 168 201 235
20 44 57 70 83 107 130 152 193 231 275
25 48 63 77 91 118 143 168 214 255 305
30 52 68 83 99 128 155 181 230 276 325
35 55 72 89 105 136 165 193 246 294 351
40 58 76 94 111 143 174 203 259 310 376

109. DRIP IRRIGATION
98
Fig. 115. Local head losses in accessories

110. DRIP IRRIGATION
99
System Layout
The drip irrigation layout presents the different components. Each of them creates
head losses when the water flows through it. In the absence of detailed data about
head losses in these accessories, a total head loss in the control head of 5 – 10 m is
assumed.
Pressure regulators are essential components of drip irrigation systems.
Whenever non-compensated drippers are in use, pressure regulators can be
installed on sub-mains and manifolds in order to control the pressure in each sub-plot.
Using one lateral per row (with row spacing of 4 m) and drippers spaced 1 m apart
along the lateral indicates spacing of 4 m2
per dripper.
7.68 Ha. = 76800 m2
divided by this spacing gives: 76800/4=19200. There are 19200
drippers in the plot. More accurate calculation can be done by multiplying row length:
4 X 80 m = 320 m, by the number of rows 320 m X 61 rows = 19520 m = 19520
drippers.
Since the drippers are not compensated, a higher flow rate than the nominal flow rate
with 10 m head should be taken into account for calculation.
Flow rate of 122/162 drippers: 2.1 l/h at 10 m, 2.57 l/h at 15 m and 3 l/h at 20 m
head.
To be on the safe side, the highest flow rate is used in the calculation and multiplied
by the number of drippers: 3 l/h X 19520 = 58.5 m3
/h.
Fig. 116. Drip system layout scheme Adapted from Watermatics brochure

111. DRIP IRRIGATION
100
Since the total flow-rate in the plot is lower than the available maximum hourly
supply, the whole plot could be irrigated in one shift. Since the spacing between the
trees is square (4 X 4 m), two lateral orientation can be checked. The above drawing
presents four different layouts. Various considerations determine selection of the best
layout. Since the plot is divided vertically, on the map, into four blocks, horizontal
orientation of on-surface laterals is to be preferred. Therefore the upper left
alternative is rejected. Of the other three alternatives, the lower left one allows
irrigation of the plot in 4 separate shifts. This allows reducing the diameter of the
distributing pipe and provides more operation flexibility.
The entire plot can be irrigated in one shift by selecting a mainline with a wider
diameter than that required for separate four shifts.
Fig. 117. Feasible layouts

112. DRIP IRRIGATION
101
The design starts with the most problematic segments, where the water flows uphill:
D-E, E-F, G-H and H-I segments (in Fig. 118).
The head losses in each of the four segments are checked. The alternatives that will
enable irrigation in one shift are examined.
Fig. 118. Segmented drawing for head loss calculation
Table 21. Calculation Form: Head losses in pipes: a. for 4 shifts
Segment Description Topographic
height initial –
distal - m
Flow
rate
Length
m
Fric.
Head
Loss %
Fric.
Head
Loss m
Topo
head
change m
Total
head loss
m
B-G 50 mm
HDPE PN 6
58.5-57.5 15 240 7 16.8 -1 15.8
B-G 63 mm
HDPE PN 6
58.5-57.5 15 240 3.6 8.6 -1 7.6
B-D 63 mm
HDPE PN 6
58.5 15 80 3.6 2.9 - 2.9
D-E 50 mm
HDPE PN 4
58.5-60 15 120 8X0.35* 3.4 +1.5 4.9
D-E 63 mm
HDPE PN 4
58.5-60 15 120 3X0.35* 1.3 +1.5 2.8
E-F 162 drip
lateral
60-60.5 0.24 80 3X0.35 1 +0.5 1.5
G-H 50 mm
HDPE PN 4
57.5-58 15 120 8X0.35 3.4 +0.5 3.9

113. DRIP IRRIGATION
102
G-H 63 mm
HDPE PN 4
57.5-58 15 120 3X0.35 1.3 +0.5 1.8
H-I 162 drip
lateral
58-59 0.24 80 3X0.35 1 +1 2
b. for one
shift B-D
63 mm
HDPE PN 6
58.5 60 80 30 24 - 24
D-G 63 mm
HDPE PN 6
58.5-57.5 30 160 10 12 -1 11
B-D 75 mm
HDPE PN 6
58.5 60 80 13 10.4 - 10.4
D-G 75 mm
HDPE PN 6
58.5-57.5 30 160 5 8 -1 7
B-D 90 mm
HDPE PN 6
58.5 60 80 6 4.8 - 4.8
D-G 90 mm
HDPE PN 6
58.5-57.5 30 160 2.4 3.8 -1 7
* 0.35 is the head loss factor for distributing pipes with more than 10 outlets
Conclusions drawn from the above table (The acceptable alternatives appear in bold
type):
a. The main line should have a minimum diameter of 63/6 mm (diameter in mm
and nominal pressure - PN in bar). Head losses in 50/6 mm pipe are too high.
b. In the manifolds - distributing pipes (D-E/G-H segments), the head loss along
a 50/4 pipe is also too high (beyond the acceptable max 10% - 15% difference
in manifolds). Hence the distributing pipes have to be also of 63/4 diameter.
c. Because of the topographic height differences, Installation of pressure
regulators at the inlets to the manifolds does not equalize adequately the head
at the inlets to the laterals. Appropriate equalization will be achieved only with
pressure regulators mounted on each outlet from the manifold.
d. That fact shows the difficulties in using non-compensated drippers in slopes.
e. If the plot is irrigated in one shift, the mainline should be 90/6 mm.
These conclusions justify
choosing the second
alternative: 2.3 l/h Ram
pressure compensated
drippers.
Spacing is the same as with
the in-line drippers, namely,
4 m between laterals and 1
m between drippers on the
lateral.
The design with
compensated drippers is
simpler. The pressure head
at the inlet to each dripper Fig. 119. The chosen diameter for mainline and manifold (in bold)

114. DRIP IRRIGATION
103
inlet has to be higher than the regulating head that activates the compensating
mechanism, which in the case of the Ram dripper is 4-5 m.
Basic calculation:
320 m row length X 61 rows = 19520 m =
19520 drippers
Total flow rate for a single shift: 19520
drippers X 2.3 l/h = 44.9 m3
/h
Since with a 20 m head at the lateral's
inlet, the maximum allowed lateral length
(on flat terrain) is 231 m, the manifold is
positioned along the N-S midline of the
plot. The plot will be irrigated in one shift,
but two valves will be installed on the
manifold to enable irrigation in two shifts.
As demonstrated in the form below, the maximum friction head loss (A-B + C-d) is
11.7 m, plus 2.5 m topographic elevation. In order to maintain an adequate head at
the last and highest dripper's inlet, the head at the outlet from control head should be
at least 20 + 14.2 m = 34.2 m.
Table 22. Head loss calculation form – Pressure Compensated (PC) drippers
Segment Description Topographic
height initial
– distal - m
Flow
rate
Length
m
Friction
Head
Loss %
Friction
Head
Loss m
Topographic
head
change m
Total
head
loss m
A-B 90 mm
HDPE PN 6
58.5-58 45 160 4 6.4 -0.5 5.9
B-C 63 mm
HDPE PN 6
58-59 22.5 120 6X0.35 2.5 +1 3.5
C-D 16 mm
lateral
59-60.5 0.37 160 6X0.35 3.3 +1.5 4.8
Fig. 120. One manifold layout

115. DRIP IRRIGATION
104
Fig. 121. Pressure compensated Ram 2.3 l/h dripper, one shift design
Irrigation Design for Field Crops and Vegetables in the Open Field
For annual field crops, the recommended method is retrievable drip irrigation. The
laterals are laid out on-surface at the beginning of the irrigation season and collected
before harvest. Distribution and retrieval of the laterals are mechanized and the level
of damage to drippers and laterals is significantly reduced by new technologies.
Example
Crop: melon
Area: 1.08 ha 120 X 90 m
Topography: flat
Spacing: 1.80 m, between rows
30 cm between plants in the row
Peak season demand: 8 mm/day
Soil: sandy-loam
Bulk density: 1.6
Field capacity: 20% v/v
Wilting point: 9% v/v
Allowable deficit 40%
Active root system depth: 60 cm
Water supply limit 30 m3
/h
Supply hours limit: 14 h a day
Fig. 122. 1.08 Ha. Of melons

116. DRIP IRRIGATION
105
Fig. 123. 10.08 Ha. Melons – In-line non-compensated drippers.
Calculation:
Daily peak demand: 8 mm = 80 m3
/Ha. = 86.5 m3
/day for the whole plot
Daily supply capacity: 30 m3
X 14 h = 420 m3
per day
In this case, non-compensated drippers can be used,
"Netafim" 162 inline dripper lateral with drippers spaced at 30 cm on the lateral is
limited to a length of 53 m. Since the length of the row is 120 m and with the manifold
at the middle of the plot a dripper with lower flow rate should be selected. It is
recommended to choose type 161 with an allowed lateral length of 83 m.
Table 23. Head loss calculation
Segment Description Topographic
height initial –
distal - m
Flow
rate
Length
m
Fric.
Head
Loss %
Fric.
Head
Loss m
Topo
head
change m
Total
head loss
m
A-B 75 mm
HDPE PN 4
- 30 90 4X0.35 1.4 - 1.4
B-C 16 mm
lateral
- 0.3 60 4X0.35 0.84 - 0.84
In this case, the non-compensated drippers are suitable (table 22). On flat land, head
differences in the irrigated plot are kept as low as 2.25 m with a 75/4 mm manifold
and the low-flow 161 dripper. This is 10% of the operating pressure, far below the
allowed upper threshold of 20% difference.

117. DRIP IRRIGATION
106
Chapter 18. DRIP IRRIGATION SCHEDULING
Drip irrigation is characterized by precise water application pattern on the one hand
and a limited wetted soil volume on the other. This requires accurate scheduling and
the implementation of a strict irrigation regime. The recommended irrigation-
scheduling method is a step-by-step process relating to all the relevant data
available.
Table 24. Irrigation scheduling – calculation form (example)

118. DRIP IRRIGATION
107
Remarks
A (General): The irrigation-scheduling process is purely mathematical. Some of the
data are not measured but estimated, such as dripper wetted volume, readily
available water percentage and crop coefficients. Hence the result of the calculations
is an estimate and should be validated in the field. Validation aids are soil moisture
and soil tension measurements, as well as physiological indicators such as shoot
growth rate, fruit growth rate, trunk expansion and midday water tension of the shoot.
C: The lower the rainfall the less its efficiency in replenishing soil moisture. Rainfall of
less than 10 mm per event is not taken into account.
F: The monthly precipitation deficit is the monthly evaporation (ET0) minus the
effective rainfall.
G, I, K: For simplification, data is given in volume per volume values. If soil moisture
data is available as weight per weight value, it is converted to volume per volume
value by multiplication by the bulk density value.
L: Readily available water is
the percentage of the available
water that can be depleted
without damaging the crop's
yield or development.
N: There are a number of ways
to estimate wetted soil volume
by a dripper. Semi-empirical formulae were applied by Schwarzmann & Zur and
Shani. When the active root-zone depth and the maximum wetting diameter are
known, a good approximation can be achieved, by relating to the wetted volume as
an ellipsoid and calculating its volume with the formula:
Vw = 4/3 (ππππr1r2r3)
Where: r1 = half of the root-zone depth
r2 = half of the maximum wetted volume diameter
r3 = the average of the two above values
T: The crop coefficient, as well as the readily available water percentage, change
along the growing season according to the crop’s sensitivity to water stress at the
different phenological stages.
X: Irrigation efficiency of drip irrigation is in the range of 80% - 90%.
Irrigation Shifts and Timetable
Once the net and the gross water applications have been calculated, a detailed
operative schedule should be elaborated.
The application per area unit (e.g. m3
/ha.) should be multiplied by the area of the plot
and compared with the water supply capacity.
For example: in the above table, the calculated water applications are in the range of
50 – 100 m3
/ha.
Clay Loam Sand
Fig. 124. Schematic wetting pattern in different textured soils

119. DRIP IRRIGATION
108
Fig. 125. Different schedules of drip irrigation operation Adapted from Benami & Ofen, 1993
Assuming a plot area of 10 ha. And a water supply limited to 30 m3
/h, 14 hours/day.
The drippers are Ram pressure compensated drippers 2.3 l/h, spaced 4 X 1 m.
Number of drippers per ha,: 10000 m2
/ 4 m2
= 2500 drippers/ha
Application rate: 2500 drippers/ha X 2.3 l/h/dripper = 5.75 m3
/h/ha
Maximum concurrently irrigated area = 30 m3
/h / 5.75 m3
/h/ha. = 5.2 ha. The 10 ha.
area should be irrigated in two shifts.
The maximum volume that can be applied during the 14 hours of water supply is:
5.75 m3
/h/ha X 14/h = 80.5 m3
/ha
This result means that during the months of June and November not enough time is
available to complete the irrigation application during a single day, and irrigation
should be continued on the following day or the irrigation interval should be reduced.
Irrigation Scheduling for Annuals
In annual crops, irrigation scheduling is related to phenological stages:
establishment, vegetative development, flowering, fruit growth and harvest.
During the first stage of establishment, only a small fraction of the surface area is
covered by foliage and the water demand is very small. On the other hand, the root
system at this stage is shallow and application frequency has to be high.
During the vegetative development stage, controlled water stress is applied to some
crops to restrict the vegetative growth in order to achieve a favorable ratio between
vegetative and reproductive development. The flowering stage is highly sensitive to
water stress. The allowed water depletion percentage in this stage is lower than at
the vegetative growth stage. The fruit development stage is less sensitive than the
flowering stage to water stress, but an adequate water regime has to be maintained
as to guarantee optimal fruit development and avoid physiological disorders.

120. DRIP IRRIGATION
109
Table 25. Irrigation scheduling form for annuals (example)

121. DRIP IRRIGATION
110
The fraction of the soil surface area covered by the foliage of annual crops during the
establishment stage is very small. Hence, drip irrigation contributes to substantial
water savings.
Operation Timetable
After the scheduling of the irrigation intervals and water applications, a timetable
should be prepared. Water supply limitations and the topography should be
considered when elaborating this timetable.
Example
Fig. 126. Layout of drip system for 55 ha. Of cotton
A 55 ha. plot of cotton should be irrigated according to the following data:
Maximum daily water requirement: 5 mm/day
Interval: 7 days
Emitters: Ram PC 1.2 l/h
Spacing: 1 X 0.5 m = 0.5 m2
Irrigation efficiency: 90%
Net weekly requirement: 7 X 5 mm = 35 mm = 350 m3
/ha
Gross weekly requirement: 350/90% = 389 m3
/ha
Number of drippers per ha. = 10000 m2
/0.5 m2
= 20,000
Application rate: 1.2 l/h X 20,000 = 24,000 l/h/ha = 24 m3
/h per ha
Max irrigation hours: 350/24 = 14.5 h
Nineteen controlled hydraulic valves divide the area to 19 sub-plots. Since the
irrigation cycle is 7 days and two spare days are reserved for maintenance and
emergency events during each cycle, 4 sub-plots must be irrigated simultaneously.

122. DRIP IRRIGATION
111
To reduce friction head-losses, each block will be irrigated in two shifts. Those sub-
plots irrigating simultaneously will be distributed along the mainline in order to
decrease head-losses.
The maximum flow rate per
shift is 242 m3
/h. The mainline
should be of 200 mm
diameter/ 60 m PN.
Due to the 7 m descending
slope, the friction head loss in
the main pipeline is
compensated by the
topographic difference gain.
The direction of the rows and
the laterals was adjusted
according to the topography
for convenience of
mechanized harvest.
Table 26. Operative Irrigation Schedule
Shift Valves Flow rate
m3
Flow rate
per shift
1 1 64
5 50
11 49
17 66 229
2 2 64
6 50
12 49
18 66 229
3 3 60
7 60
9 72
13 50 242
4 4 60
8 60
10 72
14 50 242
5 15 61
16 61
19 48 170

123. DRIP IRRIGATION
112
Chapter 19. MAINTENANCE
Drip irrigation commits careful maintenance. Particular attention should be given to
the weak points of the system:
• The narrow water passageways in the drippers that are prone to
clogging.
• The low working pressure of the piping system renders it highly sensitive to
pressure spikes.
• The filtering systems are sensitive to clogging by excessive dirt load, which
increases head losses and may decrease the filtration system performance.
• Sediments accumulate at the distal ends of the manifolds and laterals. Routine
flushing is required.
The best maintenance policy is to inspect the whole system periodically and
systematically. The time intervals between inspections depend on the water quality
and the attributes of the system's components. Inspections may be weekly, monthly,
or twice a year in favorable conditions.
Monitoring drip irrigation performance is not an easy task. The low-flow emitters do
not facilitate visual observation of application uniformity, particularly of SDI systems,
where laterals are buried underground. Nevertheless, there are some procedures
that can be implemented to roughly evaluate performance.
The first step is to check the hourly flow rate at the main flow-meter (water meter)
and compare it with the designed flow-rate (the number of emitters multiplied by the
dripper’s nominal flow-rate). Significant deviation from the designed flow rate is an
indication that there are problems in the system. A flow-rate that is lower than the
calculated value indicates possible clogging. A flow-rate that is higher than the
calculated value is an indicator of a possible rupture of the main lines or manifolds as
well as torn or punctured laterals.
The second step is to check all the pressure gauges installed in the plot and compare
the measured values to the designed pressure for each set.
If a high flow variance is suspected, on-farm inspection of dripper flow-rate uniformity
should be performed. The minimum number of drippers in a sample is 20. The
recommended number is 40-50. Once measured, the DU can be calculated. If the
DU is unacceptable, the drippers should be cleaned with acid, flushed with
pressurized air or replaced. The system should be checked again after the treatment.
Visual indicators of inadequate system performance are random stressed plants,
surface runoff, “surfacing” in SDI and white salt spots on the soil surface.
Protective measures are filtering, chlorination, acidification and flushing.
If the system includes a pumping unit, this is subject to wear and requires periodic
lubrication. Periodic pump testing, every five years (or more often if the water carries
sand) guarantees long-lasting performance.
Pressure regulators are based on spring resistance or hydraulic equilibrium
maintenance. Springs are weakened after prolonged operation and should be
inspected and calibrated once every two years.

124. DRIP IRRIGATION
113
Vacuum-relief valves perform an important function in drip systems. When the
irrigation is turned-off, the water that remains in the system flows downhill to the
lowest outlets. The water vacating the high points creates a vacuum, which causes
the emitters in this section of the plot to suck in air and dirt. In extreme cases, PVC
mainlines and thin-wall laterals may collapse. Vacuum-relief valves, installed at the
high points of the system, are prone to clogging and need periodic inspection to
guarantee that no solid objects are caught inside and that they are not stuck in the
open or shut position. Air release valves also require similar periodic examination.
The filtration system should be thoroughly inspected. In many filter types, the steel
body is coated with epoxy paint to protect it from corrosion. The intactness of the
epoxy paint should be checked routinely. Cracks in the coating endanger the
endurance of the entire body.
The collectors of sand separators, should be purged periodically, otherwise the
excess of accumulated sand reduces separation efficiency.
Screen filters should be opened and the screens visually inspected for wear, tear and
blockage by organic matter, silt and precipitates. The same is relevant for disk-type
filters.
If the filter is of the manual cleaning type, the filter element should be cleaned
carefully when the pressure difference between its inlet and outlet exceeds 5 m.
Automatic back-flushing filters require periodic visual inspection of the filtering
elements for wear and presence of persistent contaminants. Back-flushing filter
components: hydraulic valves, solenoids and rotating brushes or vacuum devices,
may require periodic servicing and lubrication. Many of them include a secondary
small water filter to protect from blockage of the solenoid ports and valve control
chambers. This filter needs periodic manual cleaning.
Automatic back-flushing media-filters fluidize and resettle the filtering bed with every
flush cycle and require special attention. The discharge of media filters should be
within the specified range of each model. For a typical 48" diameter tank, the range is
50 - 70 m3
/h. Below the lower margin, contaminants tend to infiltrate deeper into the
media bed. Flow rates higher than the recommended upper threshold can lead to
coning and channelization of the filtering media.
Coning in sand media filters is created when an excessive downwards flow striking
the diffusion plate is deflected towards the inner walls of the tank and scours the
media sand away from the walls, depositing it towards the center of the tank,
underneath the diffusion plate, creating a cone of sand.
With channelization, some areas of the tank base or the under-drain are exposed,
allowing some water to pass through the tank without contacting the filtration media,
evading filtration and potentially plugging the under-drain and the drippers on the
laterals. This can be caused by excessive downward flow rate due to coning, or by
excessive upward flow, when the tank is being back-flushed. Channelization and
coning are indicators of poor filtration. Installation of a pressure-sustaining valve may
prevent these problems.
To effectively back-flush a filter, adequate back-flush flow rate is critical, particularly
for sand filtering media. It should be large enough to fluidize and lift the filtering
media, while passing just a minor amount of sand out through the flushing discharge
manifold. The recommended back-flush flow rate for a 48" tank is 800 - 1000 l/min.

125. DRIP IRRIGATION
114
The water flushing out from the filters should be inspected visually and by touch while
a tank is back-flushing, using a 100-mesh nylon screen or by hand, to validate that
only a very small amount of media sand is being discharged from the tank.
Sometimes channelization creates sectors in the tank that are not being properly
fluidized during back flushing. Clay balls or silt stratifications are the indicators of
such a condition.
In water containing organic matter, iron, sulfur and manganese bacteria, routine
oxidation by chlorine is essential. Chlorination can be accomplished continuously
with 2 – 5 ppm of active chlorine or intermittently as a “shock treatment” when there
is a high build-up of slime in the system. A “shock treatment” with 15 – 30 ppm
chlorine is given for 20 – 30 minutes. As mentioned before, some dripper
manufacturers suggest 15 ppm as upper threshold. Higher concentrations may
damage the diaphragms in pressure compensating drippers and hydraulic valves.
Periodic flushing of the mainline, manifolds and drip laterals is an essential
maintenance practice. The best form of manually flushing is to release the lateral end
stoppers one after another and let the dirty water exit until clean water appears.
Automatic line flushing valves can be installed at lateral ends. These valves
automatically flush the laterals at the beginning of each irrigation cycle.
Fig. 127. Automatic line flushing valve Courtesy "Netafim"
Flushing also removes air that may accumulate and become trapped, especially in
laterals, due to slight undulations in the lateral. Flushing velocities should be at least
0.5 to 0.6 m/s to effectively remove air from the laterals.
Fertigation system performance should also be checked. Excessive fertilization can
induce salinity damage as well as antagonistic interference between nutrition
elements. There are four ways to check precision of nutrient application:
Collecting water samples from the dripper laterals beyond the injection
point and comparing the sample analysis with the desired
concentration.

126. DRIP IRRIGATION
115
Analyzing extracted soil solution by soil solution extractors
Analyzing the nutrient content of soil samples
In detached beds, collecting drainage samples and comparing them with
samples of water collected from drippers. If the nutrient concentration of the
drainage is significantly lower than that of the dripper emission, the rate of the
injected nutrients should be increased. The likelihood of leaching of nutrients
by excess water should also be examined. If nutrients level in drainage is
higher than that of the dripper emission, there is a possibility of excess
nutrients injection or deficit water application.
Installation Aids
There are diverse tools
to ease installation and
maintenance. Among
them are the punch
and holder that enable
precise punching of
the lateral as well as
fast and easy insertion
of connectors, splitters
and drippers into the
drilled holes.
Fig. 128. Punch (left) and holder (right) Courtesy "Netafim"

127. DRIP IRRIGATION
116
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Commercial Brochures and CD-Roms
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Netafim
Plassim
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Soil Moisture
T-Tape
Wade Rain

131. DRIP IRRIGATION
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CONVERSION FACTORS
Col.1 Col.2 Column 1 SI Unit Column 2 non-SI Unit Col.2 Col.1
multiply by multiply by
Length
0.621 kilometer, km (103 m) mile, mi 1.609
1.094 meter, m yard, yd 0.914
3.28 meter, m foot, ft 0.304
1.0 micrometer, µm (10-6 m) micron, µ 1.0
3.94 x 10-2 millimeter, mm (10-3 m) inch, in 25.4
39.4 millimeter, mm (10-3 m) mil (1/1000 inch) 0.0254
10 nanometer, nm (10-9 m) Angstrom, A 0.1
Area
2.47 hectare, ha acre 0.405
247 square kilometer, km2 (103 m)2 acre 4.05 x 10-3
0.386 square kilometer, km2 (103 m)2 square mile, mi2 2.590
2.47 x 10-4 square meter, m2 acre 4.05 x 103
10.76 square meter, m2 square foot, ft2 9.29 x 10-2
1.55 X 10-3 square millimeter, mm2 (10-3 m)2square inch, in2 645
Volume
9.73 X 10-3 cubic meter, m3 acre-inch 102.8
35.3 cubic meter, m3 cubic foot, ft3 2.83 x 10-2
6.10 x 104 cubic meter, m3 cubic inch, in3 1.64 x IO-5
2.84 x 10-2 liter, L (10-3 m3) bushel, bu 35.24
1.057 liter, L (10-3 m3) quart (liquid), qt 0.946
3.53 X 10-2 liter, L (10-3 m3) cubic foot, ft3 28.3
0.265 liter, L (10-3 m3) gallon 3.78
33.78 liter, L (10-3 m3) ounce (fluid), oz 2.96 x 10-2
2.11 liter, L (10-3 m3) pint (fluid), pt 0.473
Mass
2.20 x 10-3 gram, g (10-3 kg) pound, lb 454
3.52 x 10-2 gram, g (10-3 kg) ounce, oz 28.4
2.205 kilogram, kg pound, lb 0.454
0.01 kilogram, kg quintal (metric), q 100
1.10 x 10-3 kilogram, kg ton (2000 lb), ton 907
1.102 megagram, Mg (tonne) ton (U.S.), ton 0.907
1.102 tonne, t ton (U.S.), ton 0.907
Yield and Rate
0.893 kilogram per hectare, kg ha-1 pound per acre, lb acre-1 1.12
7.77 X 10-2 kilogram per cubic meter, kg m-3 pound per bushel, bu-1 12.87
1.49 X 10-2 kilogram per hectare, kg ha-1 bushel per acre, 60 lb 67.19
1.59 X 10-2 kilogram per hectare, kg ha-1 bushel per acre, 56 lb 62.71
1.86 X 10-2 kilogram per hectare, kg ha-1 bushel per acre, 48 lb 53.75
0.107 liter per hectare, L ha-1 gallon per acre 9.35
893 tonnes per hectare, t ha-1 pound per acre, lb acre-1 1.12 x 10-3

132. DRIP IRRIGATION
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CONVERSION FACTORS (CONTINUED)
Col.1 Col.2 Column 1 SI Unit Column 2 non-SI Unit Col.2 Col.1
multiply by multiply by
893 megagram per hectare, Mg ha-1 pound per acre, lb acre-1 1.12 x 10-3
0.446 megagram per hectare, Mg ha-1 ton (2000 lb) per acre, ton acre-1 2.24
2.24 meter per second, m s-1 mile per hour 0.447
Specific Surface
10 square meter per kilogram, m2 kg-1 square centimeter
per gram, cm2 g-1 0.1
1000 square meter per kilogram, m2 kg-1 square millimeter
per gram, mm2 g-1 0.001
Pressure / Head
10 Meter, m - water head atmosphere 0.1
9.90 mega pascal, MPa (106 Pa) atmosphere 0.101
10 megapascal, MPa (106 Pa) bar 0.1
1.00 megagram per cubic meter, Mg m-3 gram per cubic
centimeter, g cm-3 . 1.00
2.09x 10-2 pascal, Pa pound per square foot, lb ft-2 47.9
1.45X 10-4 pascai, Pa pound per square inch, lb in-2 6.90 x 103
Temperature
1.00 (K - 273) Kelvin, K Celsius, 0C 1.00 (0C +
273)
(9/5 0C) + 32 Celsius, 0C Fahrenheit, 0F 5/9 (0F - 32)
Energy, Work, Quantity of Heat
9.52 x 10-4 joule, J British thermal unit, Btu 1.05 x 103
0.239 joule, J calorie, cal 4.19
107 joule, J erg 10-7
0.735 joule, J foot-pound 1.36
2.387x 10-5 joule per square meter, J m-2 calorie per cm2 (langley) 4.19 x 104
105 Newton, N dyne 10-5
1.43 x 10-3 watt per square meter, W m-2 calorie per cm2 minute, cal cm-2 min-1 698
Plane Angle
57.3 radian, rad degrees
(angle), 0 1.75 x 10-2
Electrical Conductivity, Electricity, and Magnetism
1.0 decisiemen per meter, dS m-1 millimho per centimeter, mmho cm-1 1.0
104 tesla, T gauss, G 10-4
Water Measurement
9.73 x 10-3 cubic meter, m3 acre-inches, acre-in 102.8
9.81 X 10-3 cubic meter per hour, m3 h-1 cubic feet per second, ft3 s-1 101.9

133. DRIP IRRIGATION
122
CONVERSION FACTORS (CONTINUED)
Col.1 Col.2 Column 1 SI Unit Column 2 non-SI Unit Col.2 Col.1
multiply by multiply by
4.40 cubic meter per hour, m3 h-1 U.S. gallons per minute, gal min-1
0.227
8.11 hectare-meters, ha-m acre-feet, acre-ft 0.123
97.28 hectare-meters, ha-m acre-inches, acre-in 1.03 x 10-2
8.1 x 10-2 hectare-centimeters, ha-cm acre-feet, acre-ft 12.33
Concentration
1 centimole per kilogram, cmol kg-1 milliequivalents per
100 grams, meq 100 g-1 1
0.1 gram per kilogram, g kg-1 percent, % 10
1 milligram per kilogram, mg kg-1 parts per million, ppm 1
Plant Nutrient Conversion
Elemental Oxide
2.29 P P2O5 0.437
1.20 K K20 0.830
1.39 Ca CaO 0.715
1.66 Mg MgO 0.602

134. DRIP IRRIGATION
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