SPRINKLER IRRIGATION
TECHNOLOGY AND APPLICATION
Moshe Sne
Irrigation and Plant Nutrition Consultant
“Sprinkler Irrigation”. The publication was used as a textbook in courses on irrigation organized by the Israeli Ministry of Foreign Affairs, The Centre for International Cooperation (Mashav), through its agricultural aegis The Centre for International Agricultural Development Cooperation (CINADCO), of the Israeli Ministry of Agriculture and Rural Development.
The courses were carried-out in Israel and abroad for farmers, extension workers and policy makers in the field of irrigation and water management. They were designated for beginners and first time users of pressurized irrigation. Elucidation of the theoretical concepts was simplified to correspond with course participants' requirements.
In the last decade, irrigation technologies became more advanced and more sophisicated, perceptions and attitudes were changed, so updating this publication had been essential. The booklet covers the technology and theory of sprinkler irrigation. In addition to conventional sprinkler irrigation, two derivative technologies are dealt – micro-irrigation and mechanized irrigation. Micro-irrigation employs micro emitters of low volume water discharge with two patterns of water distribution:
a. Water is distributed through the air.
b. Water is delivered directly to the soil from drippers and bubblers.
The booklet relates only to those emitters that spread the water through the air, drippers and bubblers are excluded.
The mechanized irrigation stemmed from sprinkler irrigation. In its first generation, the emitters were solely impact sprinklers. Later-on it shifted to using micro-emitters operating at low working pressure. This technology is gaining momentum all over the world. For that reason it is covered with much more detail than in the first edition.
The manuscript emphasizes the practical aspects of sprinkler irrigation. The more advanced reader may refer to the extensive literature dealing with the subject.
Related publications are listed in the References and Bibliography list at the end of the booklet.
I have chosen to distribute the new publication by the Scribd network with the hope that users of the old version can update themselves.
TOPIC
Page
Forword
I
Table of Contents
II
List of Tables
IX
List of Figures
XI
1. INTRODUCTION
1
Overview ……….
1
Surface Irrigation ………
2
Surface Irrigation Methods ………..
2
Advanced Technologies ………...
3
2. SPRINKLER IRRIGATION
4
Introduction ……….
4
Advantages ………..
4
Disadvantages and Limitations ………...
4
Definitions ………...
5
Nominal Pipe Diameter ………
6
Sprinkler Types ………...
6
Sprinkler Classification ………
7
The Jet Angle ………...
13
Sprinkler Flow-rate ………..
14
Working Pressure (Head) ……….
14
Sprinkler Spacing, Selection and Operation ………...
14
3. MICRO-EMITTERS
16
Introduction ……….
16
Micro-emitter types ……….
17
Static Micro-emitters (Micro-jets) ………...
17
Micro-sprinklers ………...
18
Micro-sprinkler Types ……….
19
Emitter Mounting ………
20
Water Distribution Patterns ……….
21
Pump Performance Terminology ……….
24
Pump Types ………..
25
Suction Lift of a Pipe ………...
26
Kinetic Pumps ………..
27
Installation of Vertical Turbine Pumps ………
31
Submersible Pumps ………..
31
Pump Stages ……….
32
Solar water Pumps and Solar Water Pumping Systems ………...
33
Variable speed drives ………...
33
Selecting an Efficient Pumping Plant ………..
34
Maintaining Irrigation System Efficiency ………
34
The Pumping Unit Efficiency ………..
35
Cavitation ……….
37
Pump Curves ………
37
Pump and Well Testing ………
39
5. PIPES AND ACCESSORIES
40
Introduction ……….
40
Pipe Materials ………..
40
Iron, Steel and Copper ………..
40
Aluminum ……….
41
Asbestos-cement ………...
41
Concrete ………...
41
Plastic Materials ………...
41
External and Internal Pipe Diameter ………...
45
6. COUPLERS
46
Connectors (Fittings) ………...
46
Aluminum Couplers ……….
46
7. REGULATION AND CONTROL
49
Introduction ……….
49
Valves ………..
50
Control Valves – Functioning and Actuation ………..
55
Check-valves ………
58
Pressure Relief Valves ……….
59
Pressure Regulators ………..
60
Air-release Valves ………
61
Atmospheric Vacuum Breakers ………...
62
Valve Capacity ………
62
Automation ………..
62
Overview ………..
62
Flow-meters ………..
63
Metering-valves (Hydrometers) ………...
64
Control Patterns ………
64
Irrigation Timers ………..
65
Computer-based Irrigation control Systems ……….
66
Supervisory Control And Data Acquisition (SCADA) ………..
68
8. WATER TREATMENT AND FILTRATION
71
Introduction ……….
71
Particulate Matter ………
71
Biological Substances ……….
71
Chemical Precipitates ………..
72
Water hardness ………
72
Iron and Manganese in Water ………..
73
Biological Oxidation Demand (BOD)………..
73
Filtration ………..
73
Screen (Strainer) Filters ………...
73
Disc Filters ………...
75
Media Filters ………
75
Sand Seperators ………
76
Filter Location ………..
81
Supplementary Water Treatments ………...
81
Chlorination ………..
82
Acidification ……….
82
9. FERTIGATION
83
Introduction ……….
83
Advantages of fertigation ……….
83
Limitations and Risks in Fertigation ………
83
Technologies of Fertigation ………
83
Patterns of Injection ……….
83
Fertilizer Tank ………..
84
Venturi Injector ………
85
Injection pumps ………
85
Injecton Site ………
88
Injection at the Main Control Head ………..
88
Injection at Sub-main Heads ………
88
Injection at the Control Head of each Block ………
88
Control and Automation ………..
88
Quantitative Dosing ……….
88
Proprtional Dosing ………...
88
Avoiding Corrosion damage ………...
89
Back-flow Prevention ………..
89
Back-siphonage ………
89
Back-pressure ………...
89
Chemical Aspects of fertigation ………..
89
Safety ………...
90
10. FLOW-RATE – WATER HEAD RELATIONSHIP
91
Water Pressure ……….
91
Elevation Head (z) ………
91
Friction Losses ……….
92
Operating Pressure ………..
96
Hydraulic Characteristics of Emitters ……….
97
Calculation of Head Losses ……….
98
Technical data ……….
98
Pressure measurement ………..
98
Calculation of Longitudinal Head Losses ………
98
11. WATER MOVEMENT AND DISTRIBUTION IN THE SOIL
109
Soil Properties ……….
109
Soil Texture ………..
109
Soil – Water relationship ……….
111
Introduction ………..
111
Saturation ……….
111
Field Capacity
111
Wilting Point ………
111
Factors affecting the Difference in Water Storage ………...
111
Available Water Capacity (AWC) ………...
112
Water Movement in the Soil ………
112
The Determination of the Water Status in the Soil ………..
114
Water Intake Rate (WIR) of the Soil ………
115
Soil Wetting Patterns ………...
120
Water dosage ………
120
Chemical Composition of the Water ………
120
Water Distribution Uniformity ………
120
Distribution Uniformity in Fully Soil Surface Wetting Irrigation ……...
121
Distribution Uniformity in Localized irrigation ………..
129
12. SPRINKLER IRRIGATION TECHNIQUES
131
Overview ……….
131
Hand-move ………..
131
Solid-set in Orchards ………
134
Mini-sprinklers Solid-set Systems in Vegetables ………
135
Mechanized Irrigation ……….
137
Introduction ………..
137
Towline ………
137
Wheel Move ……….
138
Traveling Gun (Traveler) ……….
141
Continuous-move Sprinkler System ………
147
The Water Emitters ………..
147
Center-Pivots ………
157
Lineat-Move Systems ………...
182
Control and Automation ………...
187
13. PLANNING AND DESIGN OF SPRINKLER IRRIGATION
192
Introduction ……….
192
Planning ………...
192
Soil Properties ………..
192
Climate Data ……….
194
Cropping Data ………..
194
Water Resources ………...
194
Data Manipulation ………...
195
Soil Wetting Pattern ……….
195
Manipulation Steps ………...
196
Existing Equipment ……….
198
Calculation Formulae ………..
200
The Design Procedure ……….
201
Overview ………..
201
System Layout ………..
201
Water Flow Velocity ………
203
Spacing ……….
203
14. IRRIGATION SCHEDULING
212
Introduction ……….
212
Calculation of the Water Amount in Sprinkler Irrigation ………...
213
Calculation of the Precipitation Rate ………...
213
Calculation of the Irrigation Duration ………..
213
The Total Flow-rate of the Irrigated Area ………
213
Scheduling with the water Budget Concept ……….
214
Scheduling Software and On-line Calculators ……….
216
15. MONITORING AND CONTROL
219
Monitoring ………...
219
Soil Water Monitoring ……….
219
Plant Water Status Monitoring ……….
220
Plant Organs Elongation and Expansion ………..
221
Irrigation Control ………
221
Manual Control ………
221
Quantitative Automatic Water Shutdown ………
221
Fully Controlled Irrigation ………...
221
Integrated Irrigation and Fertigation Control ………...
221
Integrated monitoring and Control ………...
222
16. MAINTENANCE
223
Introduction ……….
223
Installation ………...
223
Mains and Sub-mains ………...
223
Laterals ……….
223
Routine Inspection ………..
224
Pump Inspection ………...
224
System Performance ……….
224
Routine Maintenance ………...
225
System Flushing and Cleaning ……….
225
Mintenance of Accessories ………...
228
Maintenance of Fertigation Systems ………
230
Chemical Water Treatments ………
230
Acidification ……….
230
Oxidation ………..
231
Overwintering of the Irrigation System ………..
231
Entire System ………...
231
Filtration Equipment ………
231
Valves ………...
231
Controllers and Sensors ………
231
Chemical Injection Equipment ……….
231
Pumps ………...
232
Electric Motors ……….
232
17. GLOSSARY
233
18. REFERENCES AND BIBLIOGRAPHY
262
LIST OF TABLES
No.
PAGE
2.1. Wind Velocity Definitions ……….
15
2.2. Recommended Spacing between Sprimklers ……….
15
5.1. PE (Polyethylene) Pipes for Agriculture ………...
42
5.2. LDPE Pipes Internal (Inner) Diameter and Wall Thickness ………….
43
5.3.
HDPE
HDPE Pipes Internal (Inner) Diameter and Wall Thickness ………….
43
5.4. PVC Pipes for Agriculture ……….
44
5.5. Internal Diameter and Wall Thickness of PVC Pipes ………
44
7.1. Flow-rate of Spring Actuated Pressure Regulators ………
61
8.1. Relative Clogging Potential of Micro-emitters by Water Contaminants
72
8.2. Screen Perforation Examples ……….
74
9.1. Electric Charges of Nutrients ………
90
10.1. Pressure and Water Potential Units ………...
91
10.2. Friction Coefficients ………
93
10.3. Multiple Outlets factor F ………
97
10.4. Effect of the Emitter Exponent on Pressure – Flow-rate Relationship .
97
10.5. Head Losses in Non-Distributing Aluminum Pipes, m. Head per
100-m. Pipe Length (without Outlets) ………..
99
10.6. F Coefficient in Laterals ………
100
11.1. Soil Classification According to Particle Diameter ………...
109
11.2. Available Water in Different Soil Textures ………..
112
11.3. Average values of Water States in Different Soil Textures – W/W ….
112
11.4. Calculating Christiansen's Coefficient of Uniformity with Experimental
Data (example) ………
127
12.1. Recommended Hose Size for Traveler Sprinklers ………
147
12.2. Characteristics and Performance of the Emitters ………..
165
12.3. Wetting Diameter of Emitters at 1.8 m
3/h Flow-rate ………
171
12.4. Recommended Spacing – m. for Emitters at 2 m. Height at Different
Working Pressures ……….
177
13.1. Sprinkler Performance (example) ……….
199
13.2. Maximum Allowed Number of Sprinklers on Lateral on Level Ground
201
13.3. The Chosen Emitter ………...
206
13.4. Allowed Length of Laterals ………...
206
13.5. Basic data ………..
207
13.6. Head-loss Calculation ………
208
13.7. Total Requested Dynamic Head ………
208
14.1. Annual Crops Irrigation Scheduling Form ………
212
14.2. The Estimated Available Water per Unit of Rooting Depth for Soils of
Various Textures and the Intake Rate for Various Soil Textures …….
214
14.3. Active Root-zone Depth of Fruit Trees ……….
215
No.
PAGE
1.1.
Level Border Strip Flooding ………
2
1.2.
Leveled Beds between Contour Lines ………..
3
1.3.
Furrow Irrigation ………..
3
2.1.
Sprinkler Spacing Positions ……….
5
2.2.
Irrigation Intensity ………
5
2.3.
The Influence of Wind on the Uniformity of Water Distribution ……
6
2.4.
Outdated Pressurized Irrigation Systems ………..
6
2.5.
Impact-Hammer Sprinkler ………
8
2.6.
Turbo-Hammer Sprinkler ……….
8
2.7.
Gun Sprinkler (Rain-gun) ……….
8
2.8.
Stand-alone Gun-sprinkler with Stabilizer in the Field ………
9
2.9.
Pop-up Sprinklers ……….
10
2.10.
Part-circle Static Sprinklers ………..
10
2.11.
Impact Sprinkler Components ………
11
2.12.
Configurations of Impact Sprinklers ………
12
2.13.
Nozzle Types ………
13
2.14.
Jet Angles ……….
13
2.15.
Low-volume Under-canopy Sprinklers ………
14
3.1.
Diverse Micro-emitters ………..
16
3.2.
Static Micro-jets ………...
17
3.3.
Vortex Sprayer ……….
18
3.4.
Vibrating Micro-jet ………..
18
3.5.
Modular Micro-emitter – Water Spreading Pattern ……….
18
3.6.
Rotating Micro-sprinklers ………
19
3.7.
Micro-sprinklers Configurations ………..
19
3.10.
Water Distribution by Micro-sprinkler at Different Flow-rates ……...
(example)
22
3.11.
Multiple-jet (Fan-jet) Emitter's Distribution Patterns ………..
22
4.1.
Schematic Plot Irrigation System ……….
23
4.2.
Electric Water Pumps ………
23
4.3.
Pump Type Classification ………
25
4.4.
Centrifugal Pump ……….
27
4.5.
Different Flow Patterns in Centrifugal Pumps ……….
28
4.6.
Water Flow in Volute Pump ………
29
4.7.
Deep-well Verical Turbine Pumps ………...
30
4.8.
Pump Impellers ………
31
4.9.
Single-stage Pump ………
32
4.10.
Multi-stage Pump ……….
32
4.11.
Solar Pumping System ……….
33
4.12.
A Variable-frequency Drive Controlls a Set of 3 Pumps …………...
33
4.13.
Pump Efficiency Curve ………
36
4.14.
A Scheme of Pump Curves ………..
37
4.15.
An Example of Pump Curves Plotted on One sheet ……….
38
4.16.
Horse-power Curves ……….
38
4.17.
Critical Points on the Pump Curve ………...
39
6.1.
Hermetic and Detached Band Couplers ………..
46
6.2.
Single Latch Couplers ……….
46
6.3.
Valve Adapters ……….
47
6.4.
Adapter Made of Al-Pb Metal Alloy ………...
47
6.5.
Aluminum Lateral Assembly ………...
47
6.6.
Plastic and Metal Connectors ………...
47
6.7.
Lock Fastened PolyPropylene Connectors
………..
48
6.8.
On-line Saddles ………
48
7.3.
Valve Types ……….
50
7.4.
Manual Actuators ……….
50
7.5.
Globe Valve ……….
51
7.6.
Angular Valve ………..
51
7.7.
Single-seat Globe Valve ………...
52
7.8.
Double-seat Globe Valve ……….
52
7.9.
Gate Valve ………
53
7.10.
Ball Valve Cutaway ……….
53
7.11.
Butterfly Valve ……….
54
7.12.
Piston Valve ……….
54
7.13.
Diaphragm Valve Components ………
55
7.14.
Diaphragm Valves ………
55
7.15.
Diaphragm Valve Working Pattern ………..
55
7.16.
Control Valve Actuators ……….…………
56
7.17.
Cutaway of Solenoid Valve ……….………
56
7.18.
Scheme of Solenoid Operation ………
57
7.19.
Fail Closed (NC) Solenoid Valve – Components and Working
Pattern ………..
57
7.20.
Hydraulic Control Valve ………..
58
7.21.
Check Valves ………
59
7.22.
Pilot Controlled Hydraulic Pressure Relief Valves ………..
59
7.23.
Pilot Valves ………..
60
7.24.
Pressure Regulators ………..
60
7.25.
Cross Section of Air-release Valves ………
61
7.26.
Atmospheric Vacuum Breakers ………...
62
7.27.
Flow-meters ……….
63
7.28.
Hydrometers – Cross-section ………...
64
7.31.
SCADA Control System ……….
68
7.32.
RTUs Connected to Field-unit (FU) by Cable ……….
69
7.33.
Internet Mediated SCADA Network ………
70
8.1.
Screen Filter ……….
73
8.2.
Screen Patterns ……….
74
8.3.
Head Losses in Clean Screen Filters ………
75
8.4.
Disc Filter ……….
75
8.5.
Media Filters ………
76
8.6.
Sand Separator - Working Pattern ………
76
8.7.
Hydro-cyclone Sand Separator – Head Losses and Optimal
Flow-rates ………..
77
8.8.
Manual Cleaning of Screen filters ………
79
8.9.
Hose Flushing of a Disc-filter ………..
79
8.10.
Continuous Flushed Circulating-filter ……….
79
8.11.
Automatic Screen Filters with Scanning Nozzles ………
80
8.12.
Automatic Flushing of Disc-filter ………
80
8.13.
High-capacity Media-filter Array ……….
81
8.14.
Back-flushing of Media-filters ……….
81
9.1.
Fertilizer Tank ………..
84
9.2.
Venturi Injector ………
85
9.3.
By-pass Venturi Installation ……….
85
9.4.
Piston and Diaphragm Hydraulic Pumps ……….
86
9.5.
No-drain Hydraulic Pump ………
86
9.6.
Piston Pump Installation in Control Head ………
87
9.7.
Fertilizer Solution Flow-meter with Pulse Transmitter
……….
87
9.8.
Mixer Array ………..
87
9.9.
Electric Pump ………...
88
10.2.
Feeding Micro-tube Connection ………...
95
10.3.
Head-losses in Hydraulic Valves ……….
95
10.4.
Pressure Measurement ………...
98
10.5.
Slide-ruler for Head-loss Calculation in Pipes ……….
101
10.6.
Nomogram for Hazen-Williams Formula ………..
103
10.7.
Nomograms for Head-loss Determination In Polyethylene Pipes ……….
104
10.8.
Nomogram for Local Hydraulic Gradient Determination in
Accessories ………
105
10.9.
Nomogram for Calculation of Head-losses in LDPE Pipes ………….
106
.
10.10
Nomogram for Calculation of Head-losses in HDPE Pipes ………….
107
10.11.
Nomogram for Calculation of Head-losses in PVC Pipes …………...
108
11.1.
Visual Illustration of Soil Particle Diameter ………
109
11.2.
Soil Texture Triangle ………...
………
110
11.3.
Illustration of the Water States in the Soil ………...
..11111111111111111111111
111
11.4.
Water-air Ratio in Two Soil Types, 12 Hours After Irrigation ………
111
11.5.
Illustration of the Available Water in the Soil ……….
112
11.6.
Water Potential Values in the Different Water States in the Soil ……
113
11.7.
Water Retention Curves in Different Soil Textures ……….
114
.
11
.8
The Sequence of Soil Moisture Determination by the Gravimetric
(Oven Drying) Method ……….
115
11.9. Edelman Dutch Auger ………..
11.10.
Water Infiltration into the Soil – Curve ………...
115
11.11.
Soil Texture Triangle – Infiltration Rate Contours ………..
116
11.12.
Typical Infiltration Curves in Different Soil Textures ……….
116
11.13.
The Basin Infiltrometer ………
117
11.14.
Double Ring Infiltrometer ………
118
11.15.
The “Sprinkler Method” ………...
119
11.18.
Simultaneously Operated Laterals Test ………
123
11.19.
Open-air Test Plot and Covered Distribution Test Facility ………….
123
11.20.
Grid of Catch Cans ………...
124
11.21.
Recording Form for Measurement of the Uniformity of Water
Distribution ………..
125
11.22.
Measured Water Amounts in One Quarter of the Wetted Area in
Single-sprinkler Test ……….
126
11.23.
Single Sprinkler Distribution Pattern in Wind-less Conditions ……...
126
11.24.
Wind Effect on the Distribution Pattern on Both Sides of a Single
Lateral ………...
128
11.25.
Unilateral Presentation of the Distribution Pattern of a Mini-emitter ….
128
12.1.
Hand-move Lateral ………..
131
12.2.
Hand-move Layout: 2” Aluminum Pipes, Spacing 6 X 12 m. 4
Laterals X 4 Positions………
……….
132
12.3.
Coupling of Aluminum Pipe ……….
132
12.4.
Ten-shift Manual Drag Under-canopy Sprinkler Array ……….
133
12.5.
Orchard Under-canopy Micro-sprinkler Irrigation ………
……….……….
134
12.6.
Solid-set System in Orchard. Spacing 6 X 4 m. Sprinkler Flow-rate …
100 l/h
134
12.7.
Orchard Overhead Irrigation ………
135
12.8.
Solid-set Mini-sprinkler Irrigation of Vegetables ………
136
12.9.
Towline ………...
137
12.10.
Towline Accessories ……….
137
12.11.
Linear Towline System: 2 Sets, 8 Laterals Each, Six Positions per
Lateral, Spacing 12X18 m ………..
138
12.12.
Sprinkler Vertically Stabilized by a Swivel and a Ballast …………...
139
12.13.
Side-roll Operating Scheme ……….
140
12.14.
Side-roll in the Field ……….
140
12.15.
Manually Moved Big Gun ……….
142
12.18.
Hose-reel Traveler Operating Scheme ………..
144
12.19.
Water-driven Cable-tow Traveler Scheme ………..
145
12.20.
Cable-tow Traveler Operating Scheme ………
145
12.21.
Linear-Move System with On-top High-pressure Impact Sprinklers
and End-gun ……….
148
12.22.
Impact Sprinkler – Nozzle Options ………..
148
12.23.
Stationary Deflection-pad Emitters ………..
150
12.24.
Nozzle and Deflection-pad Options for Stationary Spray ………
150
12.25.
Micro-emitters On-drops in Work
………..
151
12.26.
Nozzle and Pad Options in Rotators …..………..
151
12.27.
Up-right Spinner ………..…….………
151
12.28.
Rotators and Spinner ………
152
12.29.
Distinctive Emitters ………..
152
12.30.
LDN Emitters at Work ……….
153
12.31.
LDN (Low Drift Nozzle) Emitter Configurations ………
154
12.32.
Oscillating Deflection Pad Options ………..
155
12.33.
Components of Oscillating Emitters ………
155
12.34.
Inverted Wobbler on Drops ………..
155
12.35.
Diverse Configurations of Inverted Wobblers ………
156
12.36.
Quad-spray and its Water Application Modes ………
156
12.37.
Aerial View of Center-Pivot Irrigated Area ……….
157
12.38.
Center-Pivot Operation Scheme ………...
157
12.39.
Net Irrigated Area ………
157
12.40.
Components of Center-Pivot / Linear-Move Lateral System ………..
158
12.41.
Universal System (Can Be Used as Linear-Move or Center-Pivot) ….
159
12.42.
Center-Pivot Main Tower ……….
160
12.43.
Corner Arm ………..
160
12.46.
Goosenecks on Top of lateral ………...
166
12.47.
Positioning Options of Low-pressure Emitters on Drops ………
167
12.48.
Furrow Dikes ………
168
12.49.
Boom-backs behind Center-Pivot Towers ………...
169
12.50.
Bi-lateral Boom Appendage with end-gun on a Center-Pivot ……….
170
12.51.
Emitter Spacing Patterns in Center-Pivot ………..
173
12.52.
An Example of Water Logging by Spray Emitters - Close-up ………
174
12.53.
The Effect of Using Pressure Regulators in Slopy Terrain ………….
174
12.54.
Small-diameter Pressure Regulators Installed for Single Emitters ..…
.and on Drops
175
12.55.
Relationship between Width of the Wetted Coverage (W) and
Application Intensity for the Same Flow-rate ………..
176
12.56.
Relationship between Required Application Intensity and Time of
Application for the Same Depth of Application ………..
177
12.57.
Center-Pivot End-gun Installations ………..
178
12.58.
Irrigation of Orchards by Center-Pivot
……….
179
12.59.
Linear-Move Lateral ………
182
12.60.
On-lateral Trip Switch ……….
183
12.61.
Linear-Move System with Spray Emitters on Drops ………...
184
12.62.
Linear-Move System with Rotators on Drops ……….
185
12.63.
Linear-Move – Main-line in Field Margin ………...
186
12.64.
Linear-Move System Pumping Water from Ditch ………...
186
12.65.
Operation Scemes of Ditch-fed Linear-Move Systems ………
186
12.66.
VRI with Individual Emitter Control ………...
188
12.67.
VRI – Partially Irrigating Lateral ……….
189
12.68.
Individually Controlled Node ………..
189
12.69.
Control Panel Positioned in the Pivot point ……….
189
12.70.
On-screen Operation Presentation ………...
191
13.3.
Different Design Alternatives ………..
13.4.
Manifolds Save in Cost of Accessories ………
202
13.5.
Citrus Grove - 11.5 Ha. ………
204
13.6.
The Design Sceme ………
207
13.7.
Hand-move Design Scheme ……….
209
13.8.
Gun Traveler Design Scheme ………..
210
13.9.
Solid-set in Orchard ……….
211
14.1.
Typical Root Systems of Field Crops ………..
215
14.2.
Irrigation Design Software Screenshot ……….………...
216
14.3.
Visual Presention of Designed System ………
217
14.4.
Scheduling Software Screen-shot ………
217
14.5.
On-line Calculator ………
218
15.1.
Tensiometers ………
219
15.2.
Watermark Granular Sensor ……….
219
15.3.
Time Domain Transmissometry Sensor ………...
219
15.4.
The Pressure Bomb ………..
220
15.5.
Fertilizer and Water Controller ……… 221
15.6.
Integrated Monitoring and Control ………..
222
16.1.
Punch and Holder ……….
223
16.2.
Automatic Lateral End Flushing Valve ………
225
16.3.
Control Head ………
225
16.4.
Coupling of PE Pipes ………..
226
16.5.
Replacing Seal ……….
226
16.6.
Insertion of Emitters In Small-diameter Soft PE Lateral ….……….
227
16.7.
Components of Hydraulic and Metering Valves. The
Wear-sensitive Components ………
227
16.8.
Sprinkler Tools ………
227
16.11.
Vertical Stake ………...
229
1. INTRODUCTION
1.1 Overview
Water scarcity, soaring energy costs, deterioration of agricultural land and desertification, threaten agricultural development and food production for the fast growing world population.
Irrigated agriculture increases twice to ten-fold the yield per land unit, compared with non-irrigated farming.
Irrigation has its roots in the history of mankind and is even mentioned in the Bible: “A stream flows from Eden to irrigate the garden...” (Genesis, 10). The prosperous ancient civilizations developed fresh water sources and delivery systems that were used for irrigation. In years of drought, people were forced to migrate in search of water. Unfortunately, innumerable wars were triggered by water scarcity. Rivers and streams are natural water conveyors. Natural and artificial lakes are used as water reservoirs. The construction of dams converts segments of rivers' courses into reservoirs and increases their water storage capacity. Following the introduction of pumps, pipelines were installed as water conduits. The pipes are made of steel, aluminum, concrete and plastic materials. Population growth triggered long distance conveyance of water and promoted the development of water engineering and the derived science of hydraulics. Irrigation can be regarded as the science of survival. Gigantic irrigation water supply projects were built throughout the ancient world. Among them: The 1,200 km long Grand Canal in China. Water supply and irrigation systems were constructed thousands of years ago in India and Sri Lanka. Today, engineers are still impressed by the sophistication of ancient water delivery systems and the irrigation techniques employed. The Romans constructed sophisticated aqueducts, dozens of km long to deliver water to the new built cities. In Egypt, food production is fully dependent on the Aswan dam that stores water for irrigation of the Nile valley and some of the adjoining desert and guarantees food supply to the population.
Prior to the harnessing of electricity, water had to be conveyed by gravity, along natural slopes that required the construction of canal networks, for the water flow and excavating the water path accordingly. This practice had its limitation, since water could not be conveyed to the lands lying above the water sources. A remarkable revolution in irrigation technology commenced with the development of pumps that enabled lifting water above the height of the water source.
Irrigation technologies are classified into two main categories:
a. Surface (non-pressurized) irrigation - furrow, borders, flooding, basins, etc. b. Pressurized irrigation - sprinkler, spray and drip irrigation (including mechanized
irrigation).
Surface irrigation is regarded as the most wasteful irrigation technology. Irrigation efficiency is mostly below 40%. In sprinkler and mechanized irrigation, the efficiency ranges from 60% to 85%. In micro-irrigation, the efficiency can attain 90% - 95%. Salinization of irrigated lands is the most prevalent trigger of desertification (conversion of cultivated land to desert). More than one million hectares of arable land on the globe is lost annually due to salinization.
Careful water application in optimal timing and dosage with timely salt leaching when needed, is a prerequisite for long-run sustainable agriculture and inhibition of salinization.
Sprinkler irrigation, facilitates the elimination of salinization by leaching the accumulating salts out of the active root-zone by precise application of the required water amount.
There are significant differences between surface and sprinkler irrigation in the pattern of water movement and distribution in the soil. Ponding of water on the soil surface, in furrows and small basins is common in surface irrigation while water ponding in sprinkler irrigation indicates the existence of non-permeable soil layers or exessive water application rate, above the percolation capacity of the soil.
In today's raised standards of living, more attention is given to irrigation of residential and recreational facilities like home gardens, lawns, sports and golf courses. The equipment used is partially adapted from agricultural appliances and partially dedicated gear that is designed specifically for these facilities.
1.2. Surface Irrigation
Surface irrigation is the most widespread irrigation technique used on the globe. More than 90% of the 280 million irrigated hectares in the world are irrigated by surface irrigation. Surface irrigation methods can be classified into a number of techniques. The selection of the method depends on factors such as cropping technology, climate, soil type, topography, water availability and distribution facilities, farmers mentality and tradition. The most significant soil factors are the structure and the physical properties of the soil: soil texture, soil permeability; water flow on the soil surface and its movement in the soil; field capacity and wilting point; soil aeration. The most relevant climate factors are precipitation and evaporation rates during the growing season. Thorough consideration of the above-mentioned factors and incorporation of advanced techniques as zero slope leveling, SCADA (Supervisory Control And Data Acquisition) and surge (intermittent, pulsating application of water flow) irrigation, may facilitate achieving, by this “ancient technology”, efficient water use, high yields and good produce quality.
1.2.1. Surface Irrigation Methods
Fig. 1.1. Level Border Strip Flooding
1.2.1.1. Level Border Strip Flooding
The level border bed (broad-bed, or paddy) resembles a broad furrow (4 - 18 m wide), bordered by levees, with zero slope across its width and a longitudinal slope not greater than 1%. By opening the floodgate at the head of the bed, or by activating siphons, the bed is filled with water from a ditch or a furrow. This method, which is fit
for appropriately leveled topographic structures only, requires some land leveling and a high water flow-rate. Wetting the bed during a short period of time prevents water losses beneath the root zone depth. The performance of the system should be examined by field tests (advance and retreat of water as a function of time). Rice, banana, alfalfa and other field crops are usually irrigated by this method.
1.2.1.2. Leveled Beds between Contour Lines
This method is similar to border strip flooding, however the bed walls are contour lines as shown in the illustration to the right.
1.2.1.3. Furrows
The water is distributed in the field by means of narrow ditches, each of them delivering water to one or two rows of plants. Obtaining good irrigation efficiency necessitates two stages of watering. In the first stage a high flow-rate is sent to wet promptly the soil surface along the entire furrow. Then a second lower flow-rate is delivered in a longer time period.
1.2.2. Advanced Technologies
Zero slope leveling and surge irrigation are two procedures that increase irrigation efficiency in surface irrigation. These procedures can be applied with both flood and furrow irrigation.
1.2.2.1. Dead Level LayoutWhen high precision land leveling, supported by laser
sensors is applied, zero slope, dead level layout can be practical. Irrigation efficiency in this layout can be much higher than in the traditional layouts. Width of area between borders is limited to 100 – 150 m.
1.2.2.2 Surge Irrigation
The principle of surge irrigation is the splitting of water application to several pulses. The first pulse is of high volume of water. It is aimed to wet as fast as possible the entire length of the irrigated bed or furrow without inducing erosion. That first flow partially seals the upper layer of the soil and enables the next pulses to be of smaller volumes for longer time periods, rendering even depth percolation along the flow path. Modern surge irrigation layouts employ automatic surge valves that direct water in alternating pulses to different sectors of the plot according to pre-planned timetable.
Fig. 1.2. Leveled Beds between Contour Lines
2.1. Introduction
Sprinklers were first introduced at the beginning of the twentieth century as pressurized irrigation emitters for the irrigation of flower gardens. Later-on they were adapted to the irrigation of field crops, plantations and greenhouses.
Sprinkler irrigation was extensively expanded after the Second World War when aluminum became a cheap and widely available commodity and flat land, suitable for non-pressurized irrigation became scarce. Sprinkler irrigation enables simultaneous operation of many laterals of sprinklers, facilitates accurate water measurement and regulation of the water application rate to the water intake rate of the soil.
2.2. Advantages
a. Sprinkler irrigation is suitable to diverse topographic conditions like uneven lands and steep slopes that cannot be irrigated by surface irrigation.
b. A vast selection of emitters and nozzles facilitates the matching of the water application rate to the intake rate of the soil.
c. Uniform distribution of water in the field renders high water use efficiency. d. Easy and simple operation, only short training of the operators is required. e. Capability of accurate measurement of the applied water amount.
f. Prospective high mobility of the irrigation equipment from one field to another. g. The operation of solid-set and mechaniized systems, minimizes labor
requirement.
h. Feasibility of frequent - small water dosage applications for germination, cooling, frost protection, etc.
i. The closed water delivery system prevents contamination of the flowing water, decreasing the occurrence of emitter clogging.
j. Convenient blending of fertilizers with the irrigation water.
k. Handy integration with automation and computerized irrigation control devices.
2.3. Disadvantages and Limitations
a. High initial investment.
b. Extra cost of the energy consumed for creation of water pressure. c. Sensitivity to wind conditions.
d. Water losses by evaporation from soil surface, the atmosphere and plant canopy.
e. Induction of leaf-diseases in overhead irrigation.
f. Hazard of salt burns on wetted foliage in overhead irrigation. g. Washout of pesticides from the foliage in overhead irrigation.
h. Interference of irrigation with diverse farm activities like tillage, spraying, harvesting, etc.
i. Hazard of soil surface encrustation and enhancement of runoff from soil surface.
2.4.1. Pressure
: a force acting on an area, expressed in units of kg/cm2, bars, atmospheres or PSI (Pounds per Square Inch).2.4.2. Water head:
the pressure at the base of a water column, expressed in meterunits. The head in the bottom of a water column 10 m. high, is 10 m. = 1 bar. ≈ 1 atm.
2.4.3. Water amount:
measured in volume units. In the metric system the commonunits are liter (l) and cubic meter (m3) (1,000 l = 1 m3).
2.4.4. Water flow-rate (discharge):
the amount of water flowing through a certaincross-section per time unit. In the metric system the units are: m3/h or liter/h (l/h).
2.4.5. Wetting diameter:
the diameter of a circle of soil surface, wetted by acertain sprinkler = twice the wetting radius of the sprinkler. Measured in meters.
2.4.6. Sprinkler spacing:
the spacing between the sprinklers along and betweenthe sprinkler laterals. For example: 12 m x 18 m.
a. Rectangular Position b. Diagonal Position
Fig. 2.1. Sprinkler Spacing Positions
2.4.7. Irrigation Intensity:
the force of the water drops exerted on the soil surfaceduring precipitation. The intensity depends on the number of drops, their size, their velocity and the impact angle at which they hit the soil surface. The intensity is expressed in qualitative terms: high, medium, low.
a. High Intensity – Rough Droplets b. Low Intensity – Fine Droplets Fig. 2.2. Irrigation Intensity
unit per a unit of time: 1 mm/h = 1 m3 per 0.1 Ha/h = 10 m3 per Ha per hour.
2.4.8. Irrigation interval:
The time interval between two water applications = theperiod between the start of one irrigation cycle and the start of the following one.
2.4.9. Irrigation cycle:
The period between the beginning and the termination ofone irrigation event of a certain area.
2.4.10. Wind velocity:
expressed in meters per second (m/sec.) or km/h units.Fig. 2.3. The Influence of Wind on the Uniformity of Water Distribution
2.4.11. Nominal pipe diameter:
The nominal diameter of steel andasbestos-cement pipes, up to 10" is the internal diameter, measured in inches (1 inch = 25.4 mm.) In wider diameters, as well as in aluminum, plastic pipes and tubes the nominal diameter is the external diameter, measured in inches in aluminum pipes and in mm. in pipes made of plastic materials.
2.5. Sprinkler Types
In the early years, water under pressure had been applied by nozzles mounted along oscillating galvanized cast iron pipes. The oscillating movement was driven by the inherent water pressure in the irrigation system. Another means for water distribution was perforated tin pipes laid on the soil surface.
a. Skinner Oscillating Pipe System b. Perforated Pipe (Perf-O-Rain)
Fig. 2.4. Outdated Pressurized Irrigation Systems A fte r Be na m i & O fen 19 93
Contemporary sprinklers are made of metal and plastic materials. The sprinklers are mounted on metallic or plastic risers of various heights, corresponding to the irrigation technique and the crop canopy height.
Sprinklers are classified according to their function, pattern of operation, working pressure, flow-rate, materials from whom they are made, etc.
2.5.1.1. Sprinkler Function
Sprinkler function classification is based on the crop and growing technologies, for whom the sprinkler type is designated.
2.5.1.1.1. General use: Impact sprinklers with jet angle of 300, one or two nozzles, are used for overhead irrigation in field crops, forage and vegetables, as well as in overhead irrigation in orchards, in hand move, solid-set and towed laterals.
2.5.1.1.2. Under-canopy sprinklers: used for irrigation in orchards. The jet angle is 40 - 70. This group is comprised of under-canopy impact-hammers, turbo-hammers, whirling sprinklers, mini-sprinklers, microsprinklers and microjets – rotors, spinners, sprayers and ray-jets (multiple jets). These emitters are used also for solid-set irrigation in vegetables and flowers in the open field and greenhouses and in mechanized irrigation.
2.5.1.1.3. Gun sprinklers: Used for irrigation of wide-scale field crops and forage
areas, may be used as stand-alone units, in laterals, moved by hand or installed on self-propelled travelers and in center pivots and lateral move machines, as end-guns.
2.5.1.1.4. Part circle sprinklers: These sprinklers are installed at lateral ends, plot
margins and in specific situations in mechanized laterals in order to avoid water losses beyond plot borders and wetting of roads and sidewalks.
2.5.1.1.5. Regulated sprinklers: May be pressure-compensated or flow-regulated.
Simplifies design and operation in harsh topography conditions.
2.5.1.1.6. Pop-up sprinklers: Used in irrigation of lawns, golf courses and residential
areas.
2.5.1.1.7. Small-size impact and turbo-sprinklers: are used for under canopy irrigation in orchards, and overhead irrigation in open field and protected vegetables and flowers.
2.5.1.1.8. Static sprinklers are used in small residental gardens.
2.5.1.2. Pattern of Operation
Sprinklers are operated by water pressure. A water jet that is ejected from a nozzle activates the moveable component of the sprinkler.
2.5.1.2.1. Rotating impact sprinkler: The water jet, emitted from the nozzle, hits the
hammer arm, pushing it in counter-clockwise direction. A spring returns the arm back. Its strike on the sprinkler body results in rotary movement of the body in the opposite direction. The impact sprinklers are fitted with one, two or three nozzles. This sprinkler type is manufactured in diverse configurations. With a 300 ejection angle it is used for overhead irrigation of field crops and orchards. For under-canopy irrigation of orchards the recommended jet angles are 40-70.Initially. the sprinklers were made of metal, but later-on, plastic materials were also used. The wear of moving parts and nozzles made of reinforced plastic, is much lower than that of metallic ones. Although impact sprinklers are highly reliable, they require strict routine maintenance to guarantee consistent operation along time.
sprinklers are made of plastic material and are used for the irrigation of orchards, vegetables and gardens at low flow-rates.
Fig. 2.5. Impact-Hammer Sprinkler Fig. 2.6. Turbo-Hammer Sprinkler
From "Naan" Brochure 2.5.1.2.3. Gun Sprinklers
Fig. 2.7. Gun Sprinkler (Rain-gun)
Big size hammer sprinklers are made of brass with two or three nozzles. The working pressure is high (4 - 8 bars). The sprinkler flow-rate range is 6 - 60 m3/h. Gun
Center-Pivot and Lateral-Move irrigation machines and as a traveling gun in "stand-alone" configuration.
Fig. 2.8. Stand-alone Gun-sprinkler with Stabilizer in the Field
2.5.1.2.4. Pop-up sprinklers - commonly used for lawn and golf courses irrigation. The
sprinkler pops upwards at the beginning of the irrigation and falls back after shut-down into its underground housing, where it remains in stand-by position until the next irrigation. In the underground stand-by position it allows the undisturbed use of lawns, parks or golf courses, and does not interfere with lawn mowers' operation. There is a wide-range of pop-up sprinkler types, including part-circle sprinklers, as well as rise-ups of various heights.
2.5.1.2.5. Gear-driven sprinklers are used mostly in residential and public lawns irrigation. Some gun sprinklers are also driven by a turbine and velocity reduction gear.
2.5.1.2.6. Rotor and rotary stream sprinklers often incorporate a small water turbine which, by means of reducing gears, provides for slow, continuous nozzle or nozzle head rotation. Gear-drive mechanisms require clean water to prevent clogging and wear.
a. Gear-driven b. Part-circle Impact c. Pop-up Sprinkler Irrigating A Lawn Fig. 2.9. Pop-up Sprinklers
2.5.1.2.7. Static sprinklers – are
made of brass or rigid plastic materials, without moving parts. These sprinklers are used mainly in residential gardens. They irrigate a full or partial circle. The wetting range is smaller as compared to rotating sprinklers.
Manufacturers' catalogs provide the essential data about the specifications and performance of the sprinklers. Information is given about flow-rate (Q), and
the effective wetting diameter (D), in the range of the allowed working pressure (P). Additional data relate to the recommended spacing between sprinklers, the precipitation rate and distribution uniformity.
a. Fixed Angle b. Adjustable Angle Fig. 2.10. Part-circle Static Sprinklers
2.5.2.1. Base: It is the connection to
the riser. It has internal or external thread, manufactured in diameters of 0.5” - 3".
2.5.2.2. Tube: It is inserted in the base
and fixed to the body of the sprinkler. Between the base and the tube there are located 1 - 3 seals that function as bearings to smooth the rotation of the sprinkler and minimize wear from the friction of the tube with the base.
2.5.2.3. Sand protection mechanism:
Consists of a thrust spring and an external plastic sleeve that prevents the intrusion of sand and grit from the outside.
2.5.2.4. Body: Accommodates the
housings in which the nozzles are fitted and carries the moving parts of the sprinkler. The body can be of one of the configurations:
2.5.2.4.1 Bridge: In some sprinkler types, the hammer is connected to the body by means of a shaft fixed to a bridge between two vertical supports. The sprinkler rotation is activated by the impact of the hammer on one of the supports. The reverting spring surrounds the shaft.
2.5.2.4.2. Crown: Other types of sprinklers are bridge-less. The spring is connected above the hammer by a plastic or metallic crown. Under frost or dusty conditions, an external plastic cover protects the spring.
2.5.2.5. Spring: Stimulates the rotation of the sprinkler by returning the hammer arm
that was activated by the water jet that was emitted from the nozzle. In the Bridge Sprinkler, the spring is fixed within a fastening frame while in the Crown Sprinkler the spring is not fixed within the frame.
In a Crown Sprinkler, the spring tension can be adjusted to the size of the nozzle and the water head. Springs are commonly made of copper, however when using reclaimed water, stainless steel springs are recommended.
2.5.2.6. Hammer arm: Activates the sprinkler rotation. Wetting range and distribution
are determined by the number of strikes per minutes (30-60). There are two types of hammer arms:
2.5.2.6.1. Spoon drive: a rigid arm without moving parts, used in medium and high pressure conditions.
2.5.2.6.2. Wedge (dual action) drive: a plastic wedge is fitted on a shaft at the edge of Fig. 2.11. Impact Sprinkler Components
wetting.
2.5.2.7. Buffer: Absorbs partially the energy of the hammer impact to Minimize the
wear of the body by the strikes and acts as a guide to the arm.
a. Spoon Drive b. Wedge (Dual Action) Drive
c. Part-circle Sprinkler
d. Bridge Sprinkler e. Crown Sprinkler f. Protected Crown Sprinkler Fig. 2.12. Configurations of Impact Sprinklers
2.5.2.8. Nozzles
Each sprinkler is fitted with one, two or three nozzles. The nozzle type and size determine the flow-rate, the distribution pattern and uniformity and the droplets size. Nozzles are prone to wear and change of the flow-rate as well as the water distribution pattern. Irrigation water containing sand is abrasive and may expand the nozzle aperture and increase the flow-rate, as well as change the distribution pattern. Plastic nozzles are more resistant to abrasion than metallic ones.
There are different types of nozzles. A circular cross-section of the nozzle's aperture, indicates a long range jet while an elliptic or half-crescent cross-section indicates a short-range wetting diameter. Maximum range is achieved by a jet angle of 300 related to the soil surface while in under-canopy sprinklers, 40 and 70 angles are dominant. Nozzle size is expressed as its diameter in mm. Since the nozzle cross-section is not always circular, size definition may be quoted as the nominal size that is equivalent to a nozzle of circular cross-section with an identical flow-rate. Ordinarily, the nozzle size is stamped on the nozzles. In plastic nozzles it is common
Fig. 2.13. Nozzle Types After S. Elhanani, 1961
The nozzle flow-rate (Q) depends on the water pressure head, the diameter of the nozzle's aperture and its friction coefficient.
(Eq. 2.1)
Where:
Q = Nozzle flow-rate (discharge), expressed as liters per hour (l/h) P = Water pressure head, expressed in m (meters)
D = Nozzle nominal diameter, expressed in mm
C = Friction coefficient. Its value for small nozzles, up to 5.5 mm. = 0.95.
For medium size nozzles, 5.5-8 mm. = 0.9 For large nozzles, over 8 mm. = 0.85.
The pressure dependent flow-rate for a certain nozzle is:
(Eq. 2.2)
Where:
Q1 = The flow-rate at the P1 head. Q2 = The flow-rate at the P2 head.
2.5.3. The Jet Angle
The angle of the water stream ejected from the nozzle determines the range, the sensitivity to wind and the water distribution pattern. Larger angles, up to 450, render longer range but higher sensitivity to wind. For the irrigation of field crops a 300 angle is common, while for under-canopy irrigation in orchards, the prevalent angles are 40 - 70 .
a. Impact Sprinklers b. Turbo Sprinkler Fig. 2.15. Low-volume Under-canopy Sprinklers
2.5.4 Sprinkler Flow-rate
Sprinklers are classified into three groups in respect to their flow-rate.
2.5.4.1. Low flow-rate: 20 - 500 l/h. Used in orchards, greenhouses and gardens. 2.5.4.2. Medium flow-rate: 500 - 5000 l/h. Used mainly for overhead irrigation in
field crops, orchards, fodder and vegetables.
2.5.4.3. High flow-rate: Above 5 m3/h. Used in wide-spacing positioning and mechanized irrigating machines.
2.5.5. Working Pressure (Head)
2.5.5.1. Low pressure: Up to 2 bar (20 m.). Microjets, microsprinklers,
mini-sprinklers, whirling sprinklers and turbo-hammer sprinklers.
2.5.5.2. Medium pressure: 2 - 5 bar (20 - 50 m.). Impact sprinklers.
2.5.5.3. High pressure: Above 5 bar (50 m.). Gun sprinklers and large impact
sprinklers.
2.5.6. Sprinkler Spacing, Selection And Operation
There are a number of elementary factors that have to be considered in the selection of sprinklers according to distinct operating conditions:
a. The flow-rate and wetting diameter at different degrees of pressure. b. Crop spacing.
c. The desired range of the pressure and the recommended spacing between emitters.
d. Soil intake rate. The application rate has to be lower than the soil intake rate. e. Wind conditions during the irrigation season.
f. Water quality.
(Eq. 2.3)
g. Wind velocities in the plot have to be considered in the selection of the sprinkler type as well as the spacing between the sprinklers. As the wind velocity is higher, the
Table 2.1. Wind Velocity Definitions:
No wind 0 - 1.0 m/sec.
Medium wind velocity 1.0 - 2.5 m/sec. Strong wind 2.5 - 4.0 m/sec.
Very strong wind above 4.0 m/sec. Sprinkler overhead irrigation is not recommended.
Table 2.2. Recommended Spacing between Sprinklers
Positioning Wind velocity m/sec Spacing
No wind 60% of wetting diameter
2 50% of wetting diameter
3.5 40% of wetting diameter
Rectangular
More than 3.5 30% of wetting diameter
No wind 65% of wetting diameter
2 55% of wetting diameter
3.5 45% of wetting diameter
Diagonal
More than 3.5 30% of wetting diameter The diagonal (staggered) position allows for wider spacing between sprinklers under windy conditions.
The term micro-irrigation relates to pressurized irrigation technologies employing water emitters with tiny apertures that deliver water at a low flow-rate. The micro-emitters are classified into two principal groups:
a. Emitters that distribute water through the air: micro-sprinklers, rotors, spinners, wortex emitters, vibrating emitters, microjets, sprayers, rayjets and foggers. There is no definite difference between sprinklers for irrigation and the micro-emitters that distribute water through the air in micro-irrigation. There is a controversy about the distinction between macro and micro emitters – the common division boundary is 60 – 120 l/h.
b. Emitters that deliver the water directly to the soil – drippers and bubblers. These emitters are not covered in this booklet. The primary use of non-drip micro-irrigation technology is for the micro-irrigation of
orchards and greenhouses. Unlike sprinkler irrigation of field crops and vegetables, in which the desired result is rain-like uniform distribution over the entire irrigated area, in orchard irrigation, full cover and even distribution of water, is unattainable and is not necessary. The objective of orchard irrigation is to deliver a uniform amount of water to each tree and to distribute it in compliance with the distribution of the root system in the soil.
There are still orchards that are irrigated by overhead sprinklers, particularly for frost and hot spell protection. In these orchards, the sprinklers employed are of the same types that are used for irrigation of field crops. Obviously, because of the interference of the canopy in orchards, an even distribution of water on the soil surface cannot be achieved. Overhead irrigation in orchards is favored when frost protection is a significant factor in the selection of the irrigation technology. However there are many drawbacks in the use of overhead sprinkler irrigation in orchards. It interferes with pest management by leaching the pesticides from the canopy and enhances leaf and fruit diseases. The energy consumption in overhead irrigation is higher than in under-canopy irrigation.
The dominant technology in orchard pressurized irrigation, therefore, is under-canopy irrigation by low-volume, low-angle sprinklers, mini and micro-sprinklers, as well as microjets, sprayers and drippers.
Recently, the use of micro-sprinklers had been extended to irrigation of vegetables and field crops.
Micro-sprinklers are commonly built of rigid plastic materials. They are much smaller Fig. 3.1. Diverse Micro-emitters
