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STATE OF ISRAEL
MASHAV CINADCO
MINISTRY OF FOREIGN AFFAIRS
CENTRE FOR INTERNATIONAL
COOPERATION
MINISTRY OF AGRICULTURE AN...
I
CONTENTS
Chapter Topic Page
List of Tables II
List of Figures III
Foreword to The First Edition VIII
Foreword to the Sec...
II
LIST OF TABLES
No. Page
1. Pressure Units 18
2. The Friction Coefficient ( C ) of Pipes 20
3. The Effect of Dripper Exp...
III
LIST OF FIGURES
No. Page
1. Clay pot 1
2. Early patents issued for drip irrigation 2
3. Wetting pattern of drip irriga...
IV
LIST OF FIGURES (Continued)
No. Page
32. Adjustable and flag drippers 36
33. Flexible diaphragm under pressure 36
34. B...
V
LIST OF FIGURES (Continued)
No. Page
62. Hydro-cyclone sand separator – head losses and optimal flow rates 49
63. Self-f...
VI
LIST OF FIGURES (Continued)
No. Page
93. Drum kit 80
94. "Netafim" Family Drip System (FDS) 81
95. Components of Family...
VII
LIST OF FIGURES (Continued)
No. Page
124. Schematic wetting pattern in different textured soils 107
125. Different sch...
VIII
FOREWORD TO THE FIRST EDITION
The need for a comprehensive and updated book on Drip Irrigation has long been felt
as ...
IX
FOREWORD TO THE SECOND EDITION
A year has passed since the publication of the First Edition of Drip Irrigation written
...
X
ACKNOWLEGMENTS
I would like to thank my colleagues and friends, as well as the Irrigation course 2004
participants for p...
DRIP IRRIGATION
1
Chapter 1. INTRODUCTION
Drip irrigation, by definition, is an irrigation technology. However, during the...
DRIP IRRIGATION
2
pipe with a "non-clogging" leaking connection. In the year 1888, Mr. Haines of
Nashville, Iowa, register...
DRIP IRRIGATION
3
greenhouses. In 1964, he invented a drip tape for the irrigation of cantaloupes. In
1974, he developed t...
DRIP IRRIGATION
4
Chapter 2. PRINCIPLES OF DRIP IRRIGATION
Drip irrigation, sprinkler irrigation, center pivot and lateral...
DRIP IRRIGATION
5
similar, while in heavy soils the horizontal dimension of the wetted volume is greater
than that of the ...
DRIP IRRIGATION
6
• Desirable air-water equilibrium: The soil volume wetted by drip irrigation
usually retains more air th...
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7
• High initial cost: Due to the large amount of laterals and emitters, mobility of
drip systems during t...
DRIP IRRIGATION
8
Chapter 3. THE DISTRIBUTION OF WATER IN THE SOIL
The flow of water and its distribution within the soil ...
DRIP IRRIGATION
9
Soil Properties
Capillary forces are more pronounced in finer textured soils than gravity; hence the
hor...
DRIP IRRIGATION
10
Wide spacing renders wider and shallower wetting pattern.
Water Dosage
The wetted volume grows wider an...
DRIP IRRIGATION
11
The balance between the vertical and the horizontal movement is determined by soil
properties such as i...
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12
Schwarzman and Zur developed a semi-empirical formula for estimation of the
dimensions of the wetted vo...
DRIP IRRIGATION
13
The root system pattern and soil properties are important factors in determining
dripper spacing and th...
DRIP IRRIGATION
14
Chapter 4. THE DRIP SYSTEM
Although the drippers are the core of the drip irrigation network, the syste...
DRIP IRRIGATION
15
Sub-mains
The sub-mains are installed under or above ground. Underground installed pipes can
be made of...
DRIP IRRIGATION
16
when it is not under water pressure. Thick-walled laterals have a PN of 1 – 2 bar (10
– 20 m), and tape...
DRIP IRRIGATION
17
• Filtration of the irrigation water.
• Chemical treatments for decomposition of suspended organic matt...
DRIP IRRIGATION
18
Chapter 5. FLOW RATE - PRESSURE RELATIONSHIP
Water Pressure
Water pressure is a key factor in the perfo...
DRIP IRRIGATION
19
Velocity Head
Flowing water has kinetic energy (velocity energy) represented by V2
/2g where V is
veloc...
DRIP IRRIGATION
20
Where:
J = head loss (‰ =m/1000 m)
D = inner pipe diameter (mm)
C = friction coefficient (indicates pip...
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21
remember this fact for the operation of devices such as Venturi suction injectors in
drip irrigation.
A...
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Q = kPe
Where: Q = dripper flow-rate – l/h
k = dripper constant – depends on the units of flow rate and...
DRIP IRRIGATION
23
Whenever the laterals are laid out on the soil surface, the ambient temperature
affects dripper flow-ra...
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24
Technical Data
Dripper manufacturers provide detailed technical
data, in catalogues or on-line, about t...
DRIP IRRIGATION
25
Fig. 19. Head loss nomogram, based on Hazen-Williams formula
DRIP IRRIGATION
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Fig. 20 Nomogram for calculation of head losses in HDPE pipes Adapted from "Plassim" brochure
DRIP IRRIGATION
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Fig. 21 Nomogram for calculation of head losses in LDPE pipes Adapted from "Plassim" brochure
The class...
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28
Chapter 6. PIPES AND TUBES FOR DRIP IRRIGATION
The commercial development of drip irrigation is based o...
DRIP IRRIGATION
29
bars (atm). Some thin-wall laterals withstand much lower PN: 0.5 – 2 bar. The
tolerance to working pres...
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...
DRIP IRRIGATION
31
Table 10. Internal diameter and wall thickness of PVC pipes
PN------> 60 m 80 m 100 m
OD - mm ID - mm W...
DRIP IRRIGATION
32
Chapter 7. DRIPPER TYPES, STRUCTURE, FUNCTION AND PROPERTIES
Introduction
The dripper is the core of th...
DRIP IRRIGATION
33
Turbulent flow has a cleaning effect in the
corners of the water passageways.
The vortex design is anot...
DRIP IRRIGATION
34
Subsurface Drip Irrigation (SDI)
This technology has gathered momentum during the last two decades. Alt...
DRIP IRRIGATION
35
Structure and Water Passageway Characteristics
As mentioned in the introductory section, the main objec...
DRIP IRRIGATION
36
On-Line
On-line drippers are inserted into the lateral through punched holes. Drippers can be
added alo...
DRIP IRRIGATION
37
Changing of Water Flow Path Length
In another technique, pressure
compensation is applied by varying th...
DRIP IRRIGATION
38
Flap Equipped Drippers
Drippers equipped with a flap on the water outlet
prevent the suction of small s...
DRIP IRRIGATION
39
Due to the extremely low water
discharge from the emitters, more
air remains in the wetted volume,
comp...
DRIP IRRIGATION
40
Chapter 8. ACCESSORIES
In addition to drippers and pipes, drip irrigation systems are comprised of dive...
DRIP IRRIGATION
41
Control Devices
Valves are basic control devices. There are
different types of valves, each of which
pe...
DRIP IRRIGATION
42
The pressure which the water in the system exerts on the
lower face of the diaphragm reopens the valve....
DRIP IRRIGATION
43
while in the more sophisticated devices the pressure is controlled hydraulically by a
diaphragm or pist...
Drip irrigation handbook 2005
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Drip irrigation handbook 2005

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Drip irrigation, second edition
Moshe Sne, 2005

Published in: Engineering

Drip irrigation handbook 2005

  1. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 36. DRIP IRRIGATION 25 Fig. 19. Head loss nomogram, based on Hazen-Williams formula
  37. 37. DRIP IRRIGATION 26 Fig. 20 Nomogram for calculation of head losses in HDPE pipes Adapted from "Plassim" brochure
  38. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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

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