MICRO IRRIGATION TECHNOLOGY AND APPLICATION Moshe Sne Irrigation and Plant Nutrition Consultant SECOND VERSION
NOVEMBER 2009
FOREWORD Since my retirement from the Irrigation and Soil Field Service, on October 2001, after 24 years of service as field adviser and 12 years as its manager, I had been asked to share my experience and know-how with local and foreign farmers. That had been implemented in courses, surveys and counseling abroad, as well as in written publications printed by CINADCO and ICID, and in personal exchange by mail and email. Irrigation technology is so dynamic that updated publication becomes partially obsolete in two or three years. The opportunity of uploading professional material to the web by means of the Scribd system enables me to distribute in real time recently updated material. The author September 24 2009
AUTHOR'S NOTE Since the upload of the first version of this document, on September 24th, I received some dozens of e-mails from readers with comments and suggestions for improvements in the document. I found some of the comments and suggestions worthwhile to be embedded in the document. Additionally, I made adjustments on my own initiative and replaced some outdated figures in this second version. I would like to thank all the responders for their valuable contribution. November 28 2009
I
Chap.
1 2 2.1 2.2 2.3 2.4 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 5 5.1 5.2 5.3 5.4 5.5 5.6 6 6.1 6.2 6.3 6.4 6.5 6.6 7 7.1 7.2 7.3 7.4 7.5
CONTENT FOREWORD CONTENT LIST OF TABLES LIST OF FIGURES INTRODUCTION MICRO IRRIGATION Introduction ………………………………………………………………………………... Micro-emitter Classification ……………………………………………………………… Terminology ……………………………………………………………………………….. Water Distribution Uniformity ……………………………………………………………. DRIPPERS: STRUCTURE AND FUNCTION Introduction ………………………………………………………………………………... Types of Drip Systems …………………………………………………………………… Lateral type ………………………………………………………………………………... Water Passageway Structure and Characteristics ……………………………………. Position on Lateral ………………………………………………………........................ Dedicated Drippers ………………………………………………………………………. Integral Filtration in Drippers ……………………………………………………………. Auto Flushing Mechanisms ……………………………………………………………… MICRO-JETS AND MICRO-SPRINKLERS Introduction ……………………………………………………………………………….. Static Micro-jets …………………………………………………………......................... Vibrating Micro-jets ………………………………………………………………………. Micro-sprinklers …………………………………………………………………………… Bubblers …………………………………………………………………......................... Water Distribution Patterns ……………………………………………………………… Pressure Compensation …………………………………………………………………. Emitter Mounting …………………………………………………………………………. THE MICRO-IRRIGATION SYSTEM COMPONENTS The Water Source ………………………………………………………………………... The Delivery System ……………………………………………………………………... Laterals ………………………………………………………………………………….. Control and Monitoring Devices ………………………………………………………… Sub Surface Drip Irrigation (SDI) ……………………………………………………….. Low-Cost Drip Irrigation Systems ………………………………………....................... PIPES AND ACCESSORIES Polyethylene Pipes …..…………………………………………………………………… PVC Pipes ………………………………………………………………………………… Lay flat hoses …………………………………………………………………………… Fiberglass Pipes ………………………………………………………………………….. External and Internal Pipe Diameters ………………………………………………….. Accessories ……………………………………………………………………………….. WATER TREATMENT AND FILTRATION Physical Quality Parameters ……………………………………………………………. Chemical Quality Parameters …………………………………………………………… Emitter Clogging Factors ………………………………………………………………… Water Hardness …………………………………………………………………………... Iron and Manganese in Water ………………………………………………………….. II
Page I II V VI 1 2 2 2 3 4 7 7 7 8 8 10 11 14 14 15 15 16 16 16 17 18 19 20 21 21 21 22 22 24 25 28 28 29 30 30 31 31 37 37 37 37 38 38
7.6 Biochemical Oxygen Demand (BOD) ………………………………………………….. 7.7 Filtration …………………………………………………………………………………… 7.8 Supplementary Water Treatments ……………………………………………………… 8 FERTIGATION 8.1 Fertilizer Tank …………………………………………………………………………….. 8.2 Venturi Injector ……………………………………………………………………………. 8.3 Injection Pumps …………………………………………………………………………... 8.4 Injection Site ………………………………………………………………………………. 8.5 Control and Automation ………………………………………………………………….. 8.6 Avoiding Corrosion Damage ……………………………………………....................... 8.7 Back-Flow Prevention ……………………………………………………………………. 9 MONITORING AND CONTROL 9.1 Monitoring …………………………………………………………………………………. 9.2 Irrigation Control ………………………………………………………………………….. 10 FLOW RATE – PRESSURE RELATIONSHIP 10.1 Water Pressure …………………………………………………………………………… 10.2 Head Losses ……………………………………………………………………………… 10.3 Operating Pressure ……………………………………………………………………… 10.4 Hydraulic Characteristics of Emitters …………………………………………………... 10.5 Calculation of the Head Losses ………………………………………………………… 10.6 Technical Data ……………………………………………………………………………. 11 WATER DISTRIBUTION 11.1 Soil Wetting Patterns ……………………………………………………………………. 11.2 Salt Distribution …………….…………………………………………………………….. 11.3 Soil Properties that Affect Water Distribution Pattern ………………………………… 11.4 Wetting Width and Depth ………………………………………………………………... 11.5 Nutrient Distribution ………………………………………………………………………. 11.6 Root System Development Under Drip Irrigation ………………………..................... 12 PLANNING OF MICRO IRRIGATION SYSTEMS 12.1 Introduction ………………………………………………………………………………... 12.2 Planning …………………………………………………………………………………… 12.3 Data Manipulation……………………..…………………………………........................ 12.4 Existing Equipment ………………………………………………………………………. 12.5 Planning of Drip Irrigation for Different Crops …………………………...................... 13 DESIGN OF MICRO IRRIGATION SYSTEMS 13.1 Basic Guidelines …………………………………………………………....................... 13.2 The Design Procedure …………………………………………………………………… 13.3 Design of Drip Irrigation System for Row Crops ………………………………………. 13.4 Sub-Surface Drip Irrigation (SDI) ………………………………………....................... 13.5 Design of Drip Irrigation in Protected Crops …………………………………………… 13.6 Design of Irrigation Systems in Greenhouses ………………………………………… 13.7 Drip Irrigation Design for Orchards …………………………………………………….. 13.8 Design of Micro-jet and Micro-sprinkler Systems for Orchards ……………………… 14 MAINTENANCE OF MICRO IRRIGATION SYSTEMS 14.1 General ……………………………………………………………………………………. 14.2 Critical Issues in Installation …………………………………………………………….. 14.3 Routine Inspection ………………………………………………………........................ 14.4 Routine Maintenance ……………………………………………………....................... 14.5 Chemical Water Treatments …………………………………………………………….
III
39 39 47 49 49 49 50 51 51 52 52 53 53 55 57 57 58 61 62 64 64 67 67 69 69 70 70 71 72 72 72 74 78 79 85 85 85 88 98 99 100 100 110 117 117 117 118 119 122
15 16 17
NOMOGRAMS FOR ESTIMATION OF HEAD LOSSES IN PIPES AND ACCESSORIES BIBLIOGRAPHY GLOSSARY
IV
123 128 133
No.
LIST OF TABLES
6.1 6.2 6.3 6.4 6.5 6.6 7.1 7.2 7.3 7.4 7.5 10.1 10.2 10.3 10.4 10.5 10.6 10.7 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.10 13.2 13.11 13.12 13.13 13.14 13.15 13.16 13.17 13.18 13.19 13.20 13.21 13.22 13.23
PE (polyethylene) pipes for agriculture…………………………………………………. LDPE pipe internal diameter and wall thickness………………………………………. HDPE pipe inner diameter and wall thickness…………………………………………. PVC pipes for agriculture………………………………………………………………… Rigid PVC pipes internal diameter and wall thickness………………………………... Spring actuated pressure regulators……………………………………………………. Relative clogging potential of drip irrigation systems by water contaminants………. Characteristics of water passages in drippers (example)…………………………….. Screen Perforation Examples …………………………………………………………… Sand particle size and mesh equivalent………………………………………………... Nominal filter capacity – examples ……………………………………………………... Pressure and water potential units ……………………………………………………... Friction Coefficients ……………………………………………………………………… Multiple outlets factor F ………………………………………………………………….. Effect of dripper exponent on pressure – flow rate relationships ……………………. Example of integral drip lateral technical data ………………………………………… Max. Allowed lateral length for non-compensated line drippers (example) ………. Allowed lateral length for pressure compensated drippers (example) ……………… Compensating dripper (compensating pressure threshold – 4 m) data ……………. Max. Lateral length – m, Model 16012, ID = 13.70 mm, Inlet pressure 3.0 bars ….. Max. Lateral length – m, Model 16009, ID = 14.20 mm, Inlet pressure 3.0 bars ….. Non compensating thick wall dripper pressure – flow rate relationship ……………. Max. Lateral length in non compensating thick wall dripper …………………………. Non compensating thin wall dripper ……………………………………………………. . Max. Lateral length in non compensating thin wall dripper ………………………… The compatible drippers ………………………………………………………………… Design Form: COMPENSATING RAM DRIPPER 16012, 1.6 L/H, PRESSURE IN INLET 30 m Thin-wall tape data ……………………………………………………………………….. (Duplicate) Max. Lateral length – m 16012 compensating dripper laterals………… Basic data …………………………………………………………………………………. HEAD LOSSES CALCULATION FORM ………………………………………………. Head Losses In The Control Head, flow rate 56 m3/h ………………………………... Head Losses In The Hydraulic Valves On The Sub-Mains flow rate 14 m3/h ……... Total requested dynamic head …………………………………………………………. Second alternative – compensating dripper laterals – Basic data ………………….. Head-loss calculation …………………………………………………………………….. Total requested dynamic head …………………………………………………………. The chosen emitter - Non regulated Jet sprayer performance data ………………… Allowed length of laterals, Emitter type: Jet+ (Red) – lph ……………………………. Basic data …………………………………………………………………………………. Head-loss calculation …………………………………………………………………….. Total requested dynamic head …………………………………………………………..
V
Page 28 29 29 30 30 34 38 39 40 42 44 57 52 62 63 65 65 66 89 89 89 90 90 91 91 92 94 97 103 104 106 106 107 107 108 109 109 111 112 113 115 115
No.
LIST OF FIGURES
3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.1 5.2 5.3 5.4 5.5 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 7.1
Point-source (left) and line-source (right) wetting patterns by drippers ……………. In-line barbed semi-turbulent dripper and in-line integral turbulent dripper ……….. Evolution of the passageway style …………………………………………………….. Turbulent flow …………………………………………………………………………….. Orifice dripper ……………………………………………………………………………. Vortex dripper …………………………………………………………………………….. Labyrinth button dripper …………………………………………………………………. Tape dripper lateral: empty and filled with water ……………………………………... On-line drippers ………………………………………………………………………….. Button drippers connector design ……………………………………………………… Adjustable dripper and flag dripper …………………………………………………… Flexible diaphragm under pressure ……………………………………………………. Button and inline PC drippers …………………………………………………………... Cylindrical PC dripper: water passageway length changed under high pressure … Flap equipped dripper …………………………………………………………………… Woodpecker drippers ……………………………………………………………………. Arrow dripper for greenhouses, nurseries and pot plants …………………………… Six outlets dripper ……………………………………………………………………….. Ultra low flow micro-drippers …………………………………………………………… Integral dripper filters ……………………………………………………………………. Auto flushing, pressure compensating dripper ……………………………………….. Micro-emitters ……………………………………………………………………………. Modular Micro-emitters …………………………………………………………………. Static micro-jets ………………………………………………………………………….. Vibrating micro-jet, micro-sprinklers and vortex micro-jet …………………………… Modular micro-sprinkler …………………………………………………………………. Bridge micro-sprinkler and bubbler …………………………………………………….. Water distribution by micro-sprinkler at different flow rates …………………………. Ray-jet (fan-jet) distribution patterns …………………………………………………... Micro-emitters mounting alternatives ………………………………………………….. Typical layout of drip irrigation system ………………………………………………… Control head ……………………………………………………………………………… Bucket and drum kits …………………………………………………………………… Family Drip System (FDS) ……………………………………………………………… Treadle pump at work and close-up …………………………………………………… Plastic and metal connectors …………………………………………………………… Start connectors, plugs and lateral ends ……………………………………………… Lock fastened connectors ………………………………………………………………. Connectors and splitters ………………………………………………………………… Valves ……………………………………………………………………………………... Hydraulic valve operating principle …………………………………………………….. Pressure regulators ……………………………………………………………………… Control valves ……………………………………………………………………………. Air Relief Valves …………………………………………………………………………. Atmospheric vacuum breakers …………………………………………………………. Lateral-end flushing action ……………………………………………………………… Lateral-end flusher components ……………………………………………………….. Screen filter ………………………………………………………………………………. VI
PAGE 8 9 9 9 9 9 9 10 10 10 11 11 11 11 12 12 13 13 14 14 14 15 15 16 17 17 18 19 19 20 22 24 25 26 27 31 32 32 32 32 33 33 34 35 36 36 36 40
7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 1.12 8.1 8.2 8.3 8.4 8.5 8.6 8.7 9.1 9.2 9.3 9.4 9.5 9.6 10.1 10.2 10.3 10.4 10.5 11.1 11.2 11.3 11.4 11.5 11.6 11.7 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 12.10 13.1 13.2 13.3
Head losses in clean screen filters …………………………………………………….. Disc filter ………………………………………………………………………………….. Media filters ………………………………………………………………………………. Sand separator working pattern ………………………………………………………... Hydro-cyclone sand separator – head losses and optimal flow rates ……………… Automatic flushing of disk filter …………………………………………………………. High capacity media filter array ………………………………………………………… Back-flushing of media filters …………………………………………………………… High capcity automatic filter …………………………………………………………….. Compact automatic filter ………………………………………………………………… Treflan impregnated disc filter and its discs stack ……………………………………. Fertilizer tank ……………………………………………………………………………... Venturi injector …………………………………………………………………………… Piston and diaphragm hydraulic pumps ………………………………………………. No-drain hydraulic pump ………………………………………………………………... Mixer array ………………………………………………………………………………... Electric pump …………………………………………………………………………….. Tandem backflow preventer ……………………………………………………………. Tensiometers …………………………………………………………………………….. Watermark granular sensor …………………………………………………………….. Time domain transmissometry sensor ………………………………………………… . The pressure bomb …………………………………………………………………….. Fertilizer and water controller …………………………………………………………... Integrated monitoring and control ……………………………………………………… On-line Dripper Connection …………………………………………………………….. Head losses in hydraulic valves ………………………………………………………... Relationship between the dripper exponent and lateral length ……………………... Non-pressure compensating flow-pressure relationships …………………………… Pressure Compensating dripper flow-pressure relationship ………………………… Water distribution in the soil: in on-surface drip irrigation. And in SDI …………….. 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 ……………………………………………………………….. Salt distribution in the wetted volume …………………………………………………. Leaching of salt into the active root-zone by rain …………………………………….. Diverse root systems ……………………………………………………………………. Typical root systems of field crops …………………………………………………….. Root system in sprinkler irrigation vs. root system in drip irrigation .……………….. Wetting patterns by drippers in different soil types …………………………………... Ellipsoid …………………………………………………………………………………… Drip irrigation layouts in orchards ……………………………………………………… Dripper layouts in wide-spaced orchards ……………………………………………… Mechanized deployment of drip laterals ………………………………………………. Cotton root development ………………………………………………………………... Potatoes - Laterals on top of hillocks ………………………………………………….. Wide-scale drip irrigation in greenhouses …………………………………………….. Drip irrigation of potted plants in greenhouse ………………………………………… Roadside drip irrigation ………………………………………………………………….. Different design layouts …………………………………………………………………. Manifolds save accessories cost ………………………………………………………. Maize retrievable drip irrigation system layout ………………………………………..
VII
40 41 41 42 43 45 46 46 46 46 47 49 49 50 50 51 51 52 53 53 53 54 55 56 59 60 63 64 64 67 68 69 69 71 71 72 74 76 78 78 80 80 81 83 84 84 86 87 93
13.4 13.5 13.6 13.7 13.8 13.9 13.10 13.11 13.12 14.1 14.2 14.3 15.1 15.2 15.3 15.4 15.5
SDI layout ………………………………………………………………………………… thin-wall non-compensating laterals in strawberries – excessive head losses … Apple orchard – 9.6 Ha ………………………………………………………………….. Non-compensating on-line drippers flow rate -pressure relationship ………………. Two of the feasible layouts ………………………………………………………….. Non- compensating drip system ……………………………………………………….. Compensating drip system ……………………………………………………………… Citrus grove - 11.5 ha. …………………………………………………………………... Micro-jet irrigation system in citrus grove ……………………………………………... Punch and holder ………………………………………………………………………… Automatic lateral end flushing valve …………………………………………………… Vertical stake …………………………………………………………………………….. Nomogram for calculation of head losses in water flowing in pipes ………………... Nomogram for calculation of head losses in LDPE pipes. Class designation relates to the working pressure (PN) in bar …………………………………………… Nomogram for calculation of head losses in HDPE pipes. The class designation relates to the working pressure (PN) in bar …………………………………………… Nomogram for calculation of head losses in PVC pipes. The class designation relates to the working pressure (PN) in bar …………………………………………… Nomogram for calculation of local head losses in valves and other accessories and fittings …………………………………………………………………………………
VIII
98 99 101 103 104 105 108 111 114 117 119 120 123 124 125 126 127
1. INTRODUCTION 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 yield per land unit twice up to ten-fold, compared to non-irrigated farming. The principle irrigation technologies are surface irrigation, mechanized irrigation, sprinkler irrigation and micro irrigation. Surface irrigation is regarded as the most wasteful 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%. Micro irrigation is well-suited to harsh environmental conditions. Partial wetting of the soil volume, superior emission uniformity and a high level of water application control, facilitate efficient utilization of restricted water resources. The application of the water in partial, limited soil volume improves the leaching of salts out of the active root-zone. This raises the upper threshold of permitted salt content in irrigation water than with full surface wetting technologies. The frequent applications of water that are mandatory in micro irrigation dilute the soil solution and keep salt concentration low. Drip irrigation, in particular, minimizes evaporation losses from the air and soil surface compared with sprinkler, border and furrow irrigation. Salinization of irrigated lands is one of the most widespread causes of desertification (conversion of cultivated land to desert). More than one million hectares of arable land are lost every year due to salinization. Micro irrigation, particularly drip irrigation, facilitates the suspension of this process by leaching the accumulating salts out of the active root-zone. The amount of water needed for adequate salt leaching is significantly smaller than the leaching requirement in sprinkler, border and furrow irrigation. Wide-scale use of drip irrigation commenced in the Middle East, in arid regions in Israel and disseminated extensively in arid and semi-arid areas all over the world. The concept of Regulated Deficit Irrigation (RDI) - partial replenishment of the water consumed by the crop is gaining momentum in arid and semi-arid regions. Under this irrigation regime, the varying stress sensitivity in different phenological phases is exploited to reduce water dosage. In the tolerant phases, the soil water deficit is only partially replenished, maintaining the crop in mild stress that has no serious impact on yield and the produce quality. In some crops, salinity can be exploited to improve produce quality. High salt content in irrigation water improves the produce quality in tomatoes and melons, at the expense of yield. An economical balance point exists in which the premium for quality compensates for loss in yield.
1
2. MICRO IRRIGATION 2.1. Introduction The term micro irrigation refers to irrigation technologies employing water emitters with tiny apertures that deliver water at a low flow rate. There is no definite distinction between low volume sprinklers for irrigation and micro-sprinklers used in micro irrigation, but emitters with flow rates lower than 200 l/h can be regarded as micro emitters. Micro irrigation is one of the pressurized irrigation technologies alongside sprinkler irrigation and mechanized irrigation technologies. Four principal characteristics distinguish micro irrigation from the other pressurized irrigation technologies: a. Low flow rate b. Localized, partial wetting of the soil surface and soil volume while in sprinkler irrigation in field crops and vegetables the soil surface is wetted entirely. c. Frequent water applications are needed due to the limited wetted volume. d. Low operating pressure, compared with sprinkler irrigation.
2.2 Micro-emitters Classification Micro-emitters are classified in two principal groups in respect to water emitting patterns. The functional objectives of the emitters are distinctive in both groups. In the first group, water is applied directly to the soil in discrete drops (by drippers) or as a continuous stream (by bubblers). The objective of the water passageways is to maximize pressure dissipation, to approach atmospheric pressure in the emitter outlet. In the second group, water is conveyed through the air and applied to the soil as spray, mist or multiple discrete jets. Pressure dissipation is kept to a minimum in order to enable the water to be adequately spattered on the desired surface area. Each group is further subdivided in regard to the working patterns:
2.2.1. Emitters for direct application to the soil: 2.2.1.1 Drippers 2.2.1.2 Bubblers 2.2.2. Emitters for water application through the air: 2.2.2.1 Static emitters 2.2.2.1.1 Sprayers 2.2.2.1.2 Ray microjets (fan-jets) 2.2.2.1.3. Misters and foggers 2.2.2.2 Vibrating emitters 2.2.2.3 Rotating emitters
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2.2.2.3.1. Micro sprinklers 2.2.2.3.2. Rotators 2.2.2.3.3. Spinners Micro irrigation holds four obvious advantages over most other irrigation technologies: a. b. c. d.
High efficiency in water application. Improved plant nutrition management. Better salinity handling. Low energy requirement compared with sprinkler and mechanized irrigation.
The basic planning and design procedures are similar in the two micro irrigation technologies. Since drip irrigation is the most widespread technology, it receives more coverage than spray technology in this publication.
2.3. Terminology Certain terms relating to irrigation have different interpretations in micro irrigation than in conventional sprinkler irrigation.
2.3.1. Application Rate In full surface area wetting technologies such as sprinkler or border irrigation, the application rate is designated as the volume of water applied over area unit during a time unit. The application rate is expressed in units of l/m2/hour, m3/ha/hour or mm/hour. The last unit indicates the depth of the applied water volume equally spread on the irrigated area. E.g.: 1 mm water depth over 1 m2 area (1,000,000 mm2) is: 1 mm × 1,000,000 mm2 = 1,000,000 mm3 (micro liters). 1,000,000 micro liters = 1000 milliliters = 1 liter/1 m2. Since 1 ha consists of 10,000 m2, 1mm water depth = 10,000 l/ha = 10 m3/ha. In localized micro irrigation, the water does not spread evenly on the soil surface. The term Irrigation Rate (IR) designates a virtual value. The applied water quantity per hour over the irrigated area is addressed as if coverage is uniform. The virtual irrigation rate per single emitter will be its flow rate over spacing between emitters.
Example: Emitter flow rate: 2 l/h Spacing 3 × 0.5 m Irrigation Rate = 2 / (3 × 0.5) = 1.333 l/m/h = 13.33 m3/ha/h
2.3.2. Water Distribution The water that spread unevenly on the soil surface and in the soil volume makes it impractical to consider Distribution Uniformity the same as in sprinkler and border irrigation. The wetted volume by a single emitter has variable moisture levels as a function of distance from emitter, soil properties and water dose. Hence the uniformity of water distribution in micro irrigation is expressed differently than in sprinkler irrigation. The common term is Emission Uniformity (EU) that indicates the variance between emitters in a representative sample. The calculation for EU is the same as the calculation for DU but it relates to variance between emitters and not to application to area unit. 3
2.3.3. Distribution of Chemicals The distribution of dissolved chemicals (salts, nutrition elements) in micro irrigation has also different pattern than in other irrigation methods. This pattern is beneficial for nutrition and salt management but obliges strict precautions to be taken in acute climatic events like heat spells and early rains after a dry period.
2.4. Water Distribution Uniformity 2.4.1. Irrigation Efficiency Irrigation Efficiency (IE) is an important parameter for the evaluation of irrigation excellence. Water beneficially used IE =
--------------------------------------------------
(Eq. 2.1)
Total applied water
Water beneficially used is the sum of the water amounts applied for the replenishment of water used for evapo-transpiration from the plant and the soil surface, for fertilizer and pesticide application, for salt leaching, for frost protection and for crop cooling. Micro irrigation facilitates the application of even volume of water to every plant in the irrigated plot. This requires suitable spacing between laterals and emitters as well as an appropriate pressure regime. Application Uniformity can be expressed by different indices. A uniformity of 100% means that each point within the plot area gets exactly the same amount of irrigation water. When uniformity is low, certain sections of the plot receive less water than others. In order for those sections to receive sufficient amount of water, extra water amount has to be applied to the plot as a whole. As the application uniformity is lower, the required amount of extra water will be greater. Application uniformity is particularly important with drip irrigation systems, due to the cumulative nature of non-uniformity embodied in factors that determine the dripper's flow rate.
2.4.2. Distribution Uniformity A common index of application uniformity is DU (Distribution Uniformity). For calculating this value, the flow rate of a representative sample (40 - 100 emitters randomly selected in different sections of the irrigated plot) is measured. Q25% (Eq. 2.2) DU = 100 × -----------------Qn Where: Q25% is the average flow rate of 25% of the emitters with the lowest flow rate, and Qn is the average flow rate of all the sampled emitters. DU significance: >87% - excellent distribution uniformity 75% - 87% - good uniformity 62% - 75% - acceptable <62% - unacceptable. Variability in the flow rate depends on the pressure regime, the manufacturing variance of the emitters and partial emitter clogging.
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2.4.3. Manufacturer’s Coefficient of Variation (Cvm) No two emitters can be identically manufactured; there will be always a certain variation. The flow rate uniformity of new emitters is evaluated with the Manufacturing Coefficient of Variation (Cvm). Cvm indicates the variability in the flow rate of a random sample of a given emitter model, just off the production line before any field operation or degradation has taken place. The flow rate variation in manufacturing is determined statistically. Randomly selected emitter samples or a lateral segment are tested under constant pressure. The Cvm is defined as the standard deviation over the average flow rate of a sample of emitters. It is expressed as a decimal fraction or percentage. (0.01 = 1%) According to the formula:
Cvm = Where:
Sdm
--------
(Eq. 2.3)
Xm Cvm = manufacturer coefficient of variation, Sdm = standard deviation, Xm = mean flow rate.
A Cvm of 0.1 (10%) means normal distribution (a “bell shaped” curve), where 68 % of all emitter flow rates are more or less within 10% deviation from the mean flow rate. The emitter design, materials used in production, and manufacturing precision determine the variance in any particular emitter type. The standard ranking of variability is as follows: a. For point source emitters: Cvm <0.05 - excellent 0.05 - 0.07 – average 0.07 - 0.11 – marginal 0.11 – 0.15 – poor >0.15 – unacceptable With recent improvements in manufacturing technology, most emitters have Cvm < 0.10. Pressure compensating emitters have a somewhat higher Cvm than noncompensating labyrinth path emitters, due to the cumulative variability of the passageway and the compensating mechanism. b. For line source emitters (comparison of 1 m length segments): Cvm <0.10 - good 0.10 – 0.20 – average > 0.20 – marginal to unacceptable
2.4.4. Emission Uniformity The Emission Uniformity (EU) conforms to Distribution Uniformity. A controversy still exists about whether or not to consider Cvm to determine Emission Uniformity when designing irrigation systems. The stringent attitude claims that Cvm is one of the cumulative factors that determine the uniformity of water distribution and has to be taken into account.
5
In this case, Emission Uniformity will be calculated using the following formula:
[
EU =100 1.0
1.27Cvm ----------------
√n
qm
]q
(Eq. 2.4)
-------a
Where EU = the design Emission Uniformity, %. n = for a point-source emitter in a perennial crop, the number of emitters per plant; for a line-source emitter in an annual or perennial row crop, either the horizontal rooting diameter of the plants, divided by the same unit length of lateral line used to calculate Cvm or 1, which of these variables that is greater. Cvm = manufacturer’s coefficient of variation. qm = minimum emitter flow rate in the sample, l/h. qa = average or design emitter flow rate for the related sample, l/h. The lenient attitude claims that since emitters with a dissimilar flow rate are randomly located, the Cvm has to be ignored in evaluating Emission Uniformity in the design process. It has to be emphasized that the Design Emission Uniformity is relevant only for new equipment before field operation. Once the system has been operated, there is degradation of the Emission Uniformity due to full or partial clogging of emitters, deformation of emitters and compensating membranes and damage to hoses and tapes by environmental and mechanical factors. High-level maintenance, routine periodical inspections and corrective measures are required to lessen the degradation in water distribution uniformity within an irrigated plot over the long term.
2.4.5. Flow Variation of Emitters on the Lateral This compares maximum and minimum emitter flow rates along a single lateral.
qvar = (qmax - qmin)/qmax
(Eq. 2.5)
or
qvar = 1 – (qmin / qmax)
(Eq 2.6)
Where qmax is the maximum emitter flow rate, qmin is the minimum emitter flow rate, and qvar is the emitter flow rate variation. It is assumed that the manufacturer's emitter flow variation follows normal distribution so that the mean value plus two standard deviations is considered as the maximum flow rate, and the mean value minus two standard deviations is considered as the minimum emitter flow rate. This range covers over 95% of the emitter flow rates measured in the tests. Relating test results to the manufacturer’s Cvm indicates that with a manufacturing Cvm of 0.05 = 5%, the difference between maximum and minimum flow rates on the lateral may be 15%.
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3. DRIPPERS - STRUCTURE AND FUNCTION 3.1. Introduction Drippers, the core of the drip irrigation system, are small water emitters made of plastic materials. The design and production of high quality drippers is comprised of delicate and complicated processes. The basic indispensable attributes of a dripper: a. Low flow rate (discharge): 0.5 – 8 liter per hour (l/h). b. Low vulnerability to clogging. c. Low production cost and durability. Attaining low flow rate necessitates a high extent of pressure dissipation. The flow rate is determined by the pattern and dimensions of the dripper’s water passageway as well as the water pressure at the dripper inlet. The smaller the passageway crosssection, the lower the dripper flow rate at a given pressure. However, the narrower the passageway, the greater the risk of plugging by suspended solid particles and chemical precipitates. Since the dissipated water pressure en route to the dripper's outlet is a key factor in determining its flow rate, sophisticated passageway patterns have been developed for high pressure dissipation.
3.2. Types of Drip Systems Drip systems can be classified in respect to a variety of parameters:
3.2.1 Spatial Placement of Laterals 3.2.1.1. On-Surface Drip Irrigation The dominant drip technology is on-surface drip irrigation. In this arrangement, monitoring and control of the drippers' performance is convenient and effective. On the other hand, the laterals are prone to mechanical damage and degradation by solar radiation and may interfere with farming activity. In annuals, seasonal deployment and retrieval of the laterals is obligatory and annoying. In vineyards, kiwi plantations and palmetta-shaped deciduous orchards, laterals are hanged on trellises in order to relieve monitoring of dripper function and minimize mechanical damage.
3.2.1.2. Subsurface Drip Irrigation (SDI) SDI has gathered momentum over the last two decades.
3.2.1.2.1. SDI Main Advantages: a. Negligible interference with farm activity b. Elimination of mechanical damage to laterals c. Decreased weed infestation d. Elimination of runoff and evaporation from soil surface e. Improved uptake of nutrition elements by the roots, notably phosphorous.
3.2.1.2.2. SDI Main Disadvantages: a. High installation costs b. Plugging hazard by intruding roots and sucked-in soil particles c. Inconvenience in monitoring the performance of drippers and laterals d. Strict maintenance is mandatory
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3.2.2. Layout of Water Outlets along the Lateral Two typical layouts of drippers on laterals determine the water distribution pattern in the soil.
3.2.2.1. Point Sources In this layout, drippers are mounted or inserted along the laterals at length intervals that create a discrete wetted soil volume by each emitter, without overlapping. In orchard irrigation and in widely spaced annuals, thick walled hose laterals are favored.
Fig. 3.1. Point-source (left) and line-source (right) wetting patterns
3.2.2.2. Line Sources Drippers are densely positioned along the lateral, ensuring overlapping of the wetted soil volumes by adjacent drippers. This layout is typical in tape design and is the favored choice for densely grown annual crops.
3.3. Lateral Type 3.3.1. Thick-Walled Hoses Thick-walled hoses, used as drip laterals are made of Low Density Polyethylene (LDPE) of 12 – 25 mm external diameter and 1 – 2 mm wall thickness. The discrete drippers are mounted on-line or inserted inline, 10 – 100 cm apart. The normal working pressure (PN) is 1 – 4 bar (10 – 40 m).
3.3.2. Thin-Walled Laterals Thin-walled laterals may be manufactured as hoses or tapes. The thin-walled hose keeps its cylindrical cross section also when it is empty while the tape lies flat when it is not filled with water. The tapes are also made of LDPE. However, the wall thickness is only 0.1 – 0.9 mm and the PN is 0.1 – 1 bar (1 – 10 m). Laterals may be fitted with discrete molded or inserted drippers. Some tapes have contiguous pressure dissipating passageways as integral components.
3.4. Water Passageway Structure and Characteristics 3.4.1. Long Laminar or Semi-turbulent Path The water flows through a narrow, long micro-tube. The micro-tube may be long (spaghetti) or a built-in spiral in a capsulation. Water flow is laminar in the spaghetti and semi turbulent in the built-in spiral. The friction of water with the tube walls plus the internal friction between water molecules results in pressure dissipation. The flow rate of laminar-flow drippers is specifically sensitive to changes in pressure. The long
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water path and low flow velocity bring about deposition of chemical precipitates that alter the dripper's flow rate. In extreme cases, the emitter is fully plugged.
Fig. 3.2. In-line barbed semi-turbulent dripper (left) and in-line integral turbulent dripper (right)
3.4.2. Labyrinth Path The water flows along a labyrinth in which the flow direction changes abruptly. The recurrent changes in direction result in turbulent flow, high-energy losses and decreased flow rate. The labyrinth passageway is wider and shorter than the laminar path of the same flow rate. The turbulent flow flushes the corners of the twisted water path, decreasing clogging events. The flow rate in a labyrinth dripper is less affected by changes in pressure, compared with laminar flow. The short path facilitates fabrication of smaller, cheaper drippers.
Preliminary laminar design Semi turbulent dripper Labyrinth passageway Toothed (zigzag) passageway TurboNet passageway Fig. 3.3. Evolution of the passageway style Courtesy “Netafim”
Fig. 3.4. Turbulent flow from "DIS" brochure
3.4.3. Zigzag (toothed) Path This passageway form has higher pressure dissipation and better self-cleaning attributes. Enhanced version of the toothed passageway - TurboNet - allows for shorter, wider water passageways.
Fig. 3.5. Orifice dripper
Fig. 3.6. Vortex dripper
Fig. 3.7. Labyrinth button dripper
Adapted from Karmeli & Keller, 1975
Adapted from Karmeli & Keller, 1975
Courtesy "Netafim"
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3.4.4. Vortex Drippers In vortex drippers, water enters tangentially into a circular chamber, creating a spiral whirlpool that generates high head losses along a relatively short path. This allows for a wide-outlet orifice that decreases clogging hazard.
3.4.5. Orifice Drippers Pressure dissipation occurs at a tiny inlet in the bottom of the dripper, rendering it prone to plugging.
3.4.6. . Tape Laterals Trickling tapes are made of thin walled plastic tubes. When empty, the pipe lies flat. It gets a cylindrical cross section when filled with water. Water emission can take place directly through tiny perforations in the wall or through molded labyrinth passageways. The first-mentioned design is prone to partial or full clogging of the perforations and its emission uniformity degrades with time.
Fig. 3.8. Tape trickling lateral: empty (left) and filled with water (right) Adapted from "T-Tape" brochure
3.5. Position on Lateral Drippers can be mounted externally on the lateral (on-line), or inserted in-line.
Fig. 3.9. On-line drippers
Courtesy "Netafim"
3.5.1. On-Line Mounted Drippers On-line drippers are mounted through punched holes. Drippers can be added to the laterals with time to answer changes in crop development and water requirements. The dripper has a threaded or barbed joint that is screwed or inserted into thick-wall hoses. Because it protrudes from the lateral, it is prone to damage in delivery, installation and retrieval.
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Fig. 3.10. Button drippers connector design
3.5.2. In-Line Inserted Drippers In-line drippers leave the outer face of the lateral smooth. Two versions are available:
3.5.2.1. Built-in Drippers The drippers are fused into the lateral during its extrusion process.
3.5.2.2. Barbed Drippers Each dripper joins two segments of the lateral.
3.6. Dedicated Drippers 3.6.1. Adjustable Drippers 3.6.2. Flag Emitters The dripper has a twisting locker that facilitates cleansing of clogged drippers while water continues to flow in the lateral.
3.6.3. Pressure Compensating (PC) Drippers The flow rate of compensating emitters remains uniform provided the pressure in dripper's inlet is kept above a given minimum threshold. The compensating mechanism narrows or lengthens the internal water passageway as the pressure rises, adjusting the friction head losses that keep the flow rate constant.
3.6.3.1. Flexible Membrane above Water Path As the pressure above the diaphragm rises, the water passageway below the diaphragm narrows, increasing head losses and decreasing the flow rate.
Fig. 3.12. Flexible diaphragm under pressure
Fig. 3.13. Button and inline PC drippers Courtesy "Netafim"
3.6.3.2. Changing the Length of the Water Flow Path Pressure compensation is accomplished by changing the effective length of the water path. The higher the pressure the longer the effective passageway, rendering higher head loss.
Fig. 3.14. Cylindrical PC dripper: water passageway lengthened under high pressure From "Mezerplas" brochure
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3.6.4. Non-Leakage (No Drain) Drippers Draining of drip laterals after water shutdown promotes accumulation of precipitates at the bottom of the laterals and in the dripper's water passageway. Additionally, time elapses from the renewal of water supply until the laterals are filled with water and the desired working pressure builds-up. During this interval, the flow rate of the initial drippers in the lateral is significantly higher than that of the drippers at the distal end. Frequent small water applications, makes this time segment of uneven emission a significant part of the irrigation time length, decreasing application uniformity. These results generate a substantial variance in water dosage between the initial and the distal ends of the laterals and in the irrigated plot as a whole. Non-leakage drippers eliminate drain of the laterals after water shutdown by sealing the dripper's outlet as the pressure drops. This facilitates rapid pressure build-up in the laterals at the start of irrigation.
3.6.5. Flap Equipped Drippers Drippers equipped with a flap on the water outlet Fig. 3.15. Flap equipped dripper eliminate suction of small soil particles into the dripper by back siphonage at shutdown, as well as the intrusion of roots into drip laterals in subsurface drip systems. Bug cover Woodpecker
3.6.6. Woodpecker Drippers
These drippers are used in areas prone to woodpecker activity. The birds, while looking for water, drill holes in the laterals. Preventive action is taken by burying laterals with the woodpecker drippers underground and connecting thin microtubes to the dripper outlet. The distal end of the micro-tube is laid on the soil surface.
3.6.7. Trifluraline Drippers
Impregnated
For long-term prevention of root intrusion Fig. 3.16. Woodpecker drippers into subsurface drip laterals, the herbicide Trifluraline (TreflanTM) is impregnated into the drippers during the production process. After the installation of the subsurface laterals, small amounts of the herbicide are released with each water application into the soil adjacent to the dripper, sterilizing its immediate vicinity. Drippers impregnated with Trifluraline can substitute routine Treflan application for up to 15 years.
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Fig. 3.17. Arrow dripper for greenhouses, nurseries and pot plants Courtesy "Netafim"
3.6.8. Arrow Drippers Arrow dippers are used for the irrigation of potted plants. The stake-styled dripper is inserted into the growing bed. A high capacity built-in filter and efficient zigzag turbulent water passageway keep the tiny dripper unplugged and reliable for longterm use.
3.6.9. Multi-Outlet Drippers Each dripper has 2 – 12 outlets onto which small diameter micro-tubes are connected. The drippers are used mostly in landscaping and for irrigation of potted plants. Fig. 3.18. Six outlets dripper
3.6.10. Ultra Low-Flow Drippers The exceptionally low water emission rates of 0.1 – 0.3 l/h per dripper alters the water distribution pattern in the soil and other growing media. The waterto-air ratio in the wetted bed volume is altered in favor of the air. Water horizontal movement is more pronounced than with drippers of conventional flow rate. In this technology, water can be applied to shallow rooted plants with minimized drainage beneath the root-zone.
Fig. 3.19. Ultra low flow micro-drippers Adapted from "Plastro" brochure
Due to the narrow water passageways and low flow velocity, these tiny drippers are prone to clogging.
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The minute flow rate is achieved in two techniques: a. A conventional button dripper releases water into a secondary micro-tube with 10 – 30 molded or inserted micro-drippers. b. Water is applied in pulses through conventional drip laterals. The pulses are created by the irrigation controller or by dedicated pulsators. To correspond with the short pulses and long time intervals, drippers should be of the non-leakage type.
3.7. Integral Filtration in Drippers Modern high quality drippers are fitted with built-in integral filters. The filtering area increased significantly in the new models to ensure long-term high performance with reduced clogging.
Other anti-clogging means are: a. Dual water inlets and outlets per dripper. b. The barbs of on-line drippers protrude deep into the lateral, keeping the water inlet away from the dirt that accumulates on the lateral's walls. Anti-siphon devices such as the abovementioned flaps also decrease clogging occurrence.
3.8. Auto Flushing Mechanisms Certain compensating drippers are fitted with unique flexible diaphragms for releasing the debris that clog the dripper. When a solid particle blocks the water path, the diaphragm arches to widen the passageway and the clogging object is released.
Static state Pressure compensation Fig. 3.21. Auto flushing, pressure compensating dripper Courtesy "Netafim"
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Flushing
4. MICRO-JETS AND MICRO-SPRINKLERS 4.1. Introduction Micro emitters that disperse water through the air are used extensively in orchard irrigation. Unlike sprinkler irrigation used in field crops and vegetables where water is distributed evenly over the entire irrigated area, in orchard irrigation, full soil surface coverage and even distribution of water is unattainable and is not necessary. The objective of orchard irrigation is to deliver equal amounts of water to each tree and to distribute it in compliance with the root system distribution pattern in the soil. Under-canopy irrigation is common in orchard irrigation. It can be carried out by low-volume, lowangle mini sprinklers as well as by micro-sprinklers, micro-jets, sprayers, drippers and bubblers. Recently, the use of micro-sprinklers had been extended to irrigation of vegetables and field crops. Micro-emitters built of rigid plastic materials are much smaller and cheaper than conventional sprinklers. Four emitter types are available: a. Static micro-jets b. Micro-jets with vibrating deflector c. Micro-sprinklers - spinners and rotators d. Vortex Emitters
Fig. 4.1 Micro-emitters
The operating pressure is 10 – 30 m., somewhat higher than in drip systems. The water distribution range at a given pressure depends on the nozzle geometry, emission pattern flow rate and water pressure (head). Many types of micro-sprinklers are modular. Components are interchangeable and facilitate low cost modification of flow rate, droplet size, distribution pattern and range. Changing the deflector and nozzle makes the difference.
Fig. 4.2. Modular Micro-emitters Courtesy "Naan-Dan"
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Deflectors in diverse configurations allow sectorial coverage from 450 to 3600.
4.2. Static Micro-jets Static micro-jets have no moving components and are classified into three groups:
4.2.1. Sprayers – the water stream is fragmented into tiny droplets by means of a static deflector. Water is distributed in a relatively short range and the tiny drops are wind sensitive.
4.2.2. Misters and Foggers – water droplets are smaller than in sprayers. Spread range is shorter. Wind sensitivity and evaporation losses are higher than in sprayers. This type is mostly used to increase the humidity in greenhouses and poultry coops, as well as for frost protection in orchards. 4.2.3. Ray-Jets (Fan-Jets) – the water stream is spitted into 4 – 20 discrete jets. The range is extended and wind sensitivity is reduced.
Static sprayer
Mister
Fogger
Ray-jet
Fig. 4.3. Static micro-jets
4.3. Vibrating Micro-jets Water ejected from a circular orifice strikes a deflector and triggers it to vibrate. The vibration of the deflector creates larger drops than in sprayers, increases the distribution range and reduces evaporation and wind sensitivity.
4.4. Micro-sprinklers 4.4.1. Rotators are manufactured in different configurations. The central shaft with the nozzle is static. The water jet hits a rotating deflector that distributes water in larger area than the vibrating emitters.
4.4.2. Spinners - the nozzle rotates and further increases the jet range. The movement of components in micro-sprinklers increases their sensitivity to the interference of factors like weeds, precipitates and splashed soil particles. It also accelerates wear and tear. The damage hazard from herbicide sprayer booms and other tillage equipment is particularly increased during harvest operations.
4.5. Vortex Emitters These emitters have no moving parts. The water revolves in a circular vortex chamber that delivers a low flow rate through a relatively large opening that reduces
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the clogging hazard. The area wetted by this emitter is smaller than in other emitter types.
Vibrating sprayer
Rotator
Spinner
Vortex sprayer
Fig. 4.4. Vibrating micro-jet, micro-sprinklers and vortex micro-jet
Micro-sprinkler components
Interchangeable components
Fig. 4.5. Modular micro-sprinkler Pressure compensating and flow regulated micro-emitters are particularly suitable for irrigating steep sloping plots. Micro-sprinkler systems require a higher volume of water supply compared to onsurface or buried drip systems.
4.6. Bubblers In Bubblers, as with drippers, the water pressure dissipates almost fully on its way to the outlet, but the discharge is much higher: 20 – 200 l/h. The water flows from the 17
bubbler along its stake or spreads adjacent to it. The pressure is dissipated through diaphragms and small orifices. Bubblers may be pressure compensating. Multiple outlets are available. In some cases the use of bubblers requires the excavation of small basins around the emitter to prevent runoff. Micro-emitters are mostly connected to the laterals by means of a plastic micro tube. They are mounted on a stake or a rod to stabilize their vertical position at 10 - 25 cm above ground level. Threaded micro-emitters are installed on 1/2" – 3/4" rigid PVC risers. Barb micro-emitters can be mounted directly on the lateral. In greenhouses, microemitters may be installed upside down for overhead irrigation and misting. Weights are hung to stabilize them vertically.
Unilateral bridge
Bridge type micro-emitters provide improved support to the rotating spinner or deflector, but the vertical supports of the bridge creates dry sectors behind them. Micro-emitters are as prone to clogging Bubbler as drippers, but when clogging occurs it Bi-lateral bridge is quickly noticed and easily cleaned. Fig. 4.6. Bridge micro-sprinkler and bubbler Some emitters are equipped with a small integral valve to enable local water shutdown during the cleaning process. Some types of micro-sprinklers are prone to clogging by the eggs and excretions of spiders, ants and other insects. Insect-proof devices have been developed to prevent these obstructions. Ant and bug caps may be added to discourage ants and other insects from intruding into the system. Spiders are capable of tying up spinners and halt their rotation. Micro-sprinkler operation can be disturbed by sand that is splashed upward from the soil surface when hit by droplets from adjacent emitters. Plugs that are not removed on time in orchards that employ one emitter per tree may result in lower yields and reduced produce quality.
4.6. Water Distribution Patterns The emitter’s water distribution pattern depends on its outlet (nozzle) and deflector geometry, trajectory angle, droplets size, pressure and flow rate. The higher the trajectory angle (up to 450) and the larger the droplet size and flow rate, the larger will be the wetting diameter. The patterns of water distribution and wetting depth in the wetted area vary with the emitter type. In some emitters the wetting pattern is triangular. These emitters are suitable for overlapping and full wetting of the soil
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surface. In some emitters the deeper wetting depth is adjacent to the emitter while in others it is uniform in most of the wetted area.
Fig. 4.7. Water distribution by micro-sprinkler at different flow rates (example)
Fig. 4.8. Ray-jet (fan-jet) distribution patterns From "Bowsmith" Brochure
4.7. Pressure Compensation Like drippers, micro-sprinklers and micro-jets can be pressure compensating. That facilitates longer laterals and uniform application in harsh topographic conditions.
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4.8. Emitter Mounting Emitters can be mounted directly on the lateral attached by a barbed or threaded protrusion. The preferred connection to the lateral is by means of a small diameter micro-tube. The vertical position is secured by a stake, stabilizing rod or stabilizing tube. The emitter is raised 10 – 25 cm above soil surface to prevent halt of rotation of the moving parts by weed interference and splashed soil particles. The micro-tubes are 50 – 100 cm long and 4 – 8 mm in diameter. Diameter of 6 - 8 mm is preferred for emitter flow rates over 60 l/h and when the micro-tube length is over 60 cm, to prevent excessive head losses. In greenhouses, micro-sprinklers, misters and foggers are frequently used to increase the relative humidity and lower the temperature of the ambient atmosphere. The misters and the foggers emit tiny droplets and are operated intermittently in pulses. These emitters are often mounted upside-down with the trajectory angle slanted downwards, in order to avoid hitting the glass or plastic ceiling.
Sprayer on Upside-down misters Micro-sprinkler on rod stake with stabilizing tubes Fig. 4.9. Micro-emitters mounting alternatives
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Upside-down Micro-sprinkler
5. THE MICRO IRRIGATION SYSTEM Water emitters are the end devices of the micro irrigation system which is composed of a variety of interconnected components. The constituents of the system are classified into six principal categories:
a. Water Source: river, lake, reservoir, well, or connection to a public, commercial or cooperative water supply network. Micro irrigation is a pressurized irrigation technology in which water is delivered from the source by increasing its internal energy (pressure) by pumping.
b. Delivery System: Mainline, submains and manifolds (feeder pipes). c. Emitter Laterals d. Control Devices: Valves, flow meters, pressure and flow regulators, automation equipment, backflow preventers, vacuum and air release valves, etc.
e. Filtration Devices f. Chemical Injectors: for introduction of plant nutrients and water treatment agents into the irrigation water.
5.1 The Water source 5.1.1. The Water Supply Control Head There are two alternative sources of water supply: a. Direct withdrawal from an on-surface source (such as a 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. If pumping is needed, the pump will be chosen according to the required flow rate and pressure in the irrigating system. When connected to a water supply network, the diameter of the connection, main valve and the delivering line should correspond with the planned flow rate and working pressure in the irrigated area.
5.2. The Delivery System 5.2.1. Mainlines for Water Delivery and Distribution: Pipes are made of PVC or polyethylene (PE). Ordinary PVC pipes have not UV protection and should be installed underground. Recently, unplasticized PVC (UPVC) pipes are manufactured with reduced sensitivity to UV and better endurance than common PVC pipes. PE (polyethylene) pipes can be installed inside or above ground, as they are impregnated with carbon black that provides counter UV protection. The pipes’ nominal working pressure (PN) has to be higher than that of the drip laterals, particularly if the system has to withstand pressure fluctuations with while valves are closed. The common PN of delivery and distribution mainlines is 6 – 8 bar (60 – 80 m dynamic head).
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5.2.2. Submains Submains are installed underground (PVC or PE) or above ground (PE only). In retrievable drip systems in annual crops, above-ground pipes are made of PE, aluminum or vinyl “lay flat” hose.
5.2.3. Manifolds In certain circumstances, when rows are very long or in harsh topography, subdivision of the plot by submains is insufficient. In these cases secondary partition is carried out by manifolds. Manifolds are used also to simplify operation and to lower accessories costs.
Fig. 5.1. Typical layout of micro irrigation system
5.3. Laterals Laterals are made mostly of LDPE (Low Density Polyethylene). PVC laterals are used on a limited scale. The laterals may be laid on the soil surface or underground. Shallow burying of drip laterals, 5 – 10 cm below soil surface is suitable to vegetables grown on hillocks or under plastic mulch.
5.4. Control and Monitoring Devices 5.4.1. Valves and Gauges 5.4.1.1. Manual or automatic valves are used for the opening and shutdown of water and for splitting the irrigated area into sectors. Water-meters (flow meters) are used to measure the amount of water delivered.
5.4.1.2. Pressure regulators prevent excessive pressure beyond the working pressure of the system.
5.4.1.3. Check valves and backflow preventers are required when fertilizers or other chemicals are injected into the irrigation system, if the irrigation system is connected to potable water supply network.
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5.4.1.4. Air-release/relief valves are installed in the higher points of the system to eliminate air flow in the pipes. High air content in the pipes may interfere with water flow, increase friction with pipe walls, distort water measurement and may cause water hammer and pipe burst. 5.4.1.5. Vacuum breakers prevent the collapse of pipes in steep slopes and drip laterals in Sub-surface Drip Irrigation (SDI) systems. In SDI they also eliminate the suction of soil particles into the drippers after shutdown of the water supply.
5.4.2. Filtration In micro emitters, the narrow water passageways are susceptible to clogging by suspended matter and chemicals that precipitate from the irrigation water. Clogging can be eliminated by: a. Preliminary separation of suspended solid particles by settling ponds, settling tanks and sand separators. b. Complimentary chemical treatments for decomposition of suspended organic matter; to hinder the development of slime by microorganisms; to prevent chemical precipitates deposition and to dissolve previous deposited precipitates. c. Filtration of the irrigation water. Filtration devices are usually installed at the control head. If the irrigation water is heavily contaminated, secondary control filters are installed at the sectorial valves. Filters should be flushed and cleaned routinely. Flushing can be done manually or automatically. Automatic back-flushing of media filters is performed with filtered water, hence, the filters are installed in arrays of two or more units and the filters are flushed in sequence one after another.
5.4.3. Chemical Injectors Three categories of chemicals are injected into irrigation systems: fertilizers, pesticides, and anti-clogging agents. •
Fertilizers are the most commonly injected chemicals; the capacity to “spoonfeed” the crop with nutrients, increases yields with micro irrigation.
•
Systemic pesticides are injected into drip irrigation systems to control insects and protect plants from a variety of diseases.
•
Chemicals that clean drippers or prevent dripper clogging.
Chlorine is used to kill algae and different microorganisms and to decompose organic matter, while acids are used to reduce water pH and dissolve precipitates. The different types of injectors are described in the chapter on fertigation.
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Fig. 5.2. Control head Courtesy " Netafim"
5.5. Sub-surface Drip Irrigation (SDI) Since the early eighties, sub-surface drip irrigation technology has gained momentum.
Advantages of SDI: a. Elimination of interference with farming activities b. Reduced soil compaction c. Elimination the burden of laying and retrieving laterals in annual crops d. Protection of laterals from mechanical and environmental damage e. Water conservation, Avoidance of direct evaporation from soil surface f. Decreased weed infestation g. Improved nutrient application efficiency h. suitable for utilization of reclaimed water for irrigation of edible crops
Limitations of SDI: a. High initial cost b. Inconvenient monitoring of water application and expensive maintenance c. Increased emitter clogging hazard by penetrating roots and sucked soil particles d. Water "surfacing" – unintended soil surface wetting by capillary upward water movement e. High water loss by deep percolation in cracking soils f. Germination irrigation has to be with sprinklers in some crops g. Limits the depth of land tillage h. difficulties with crop rotation i. Prone to damage by rodents 24
In Sub-Surface Drip Irrigation (SDI), drip laterals are buried 10 – 50 cm below the soil surface.
5.6. Low-cost Drip Irrigation Systems In many developing countries, irrigation is used for growing fruit and vegetables for own consumption in family-owned gardens, some of which on area of 20 – 500 m2. These gardens are mostly furrow-irrigated with water drawn from shallow wells, rivers, lakes and reservoirs; either by hand, animals or by small motor-driven pumps. In the last decade, productivity has impressively improved by replacement of furrow irrigation with small scale systems of drip irrigation. Conventional drip technology is not suitable for these small gardens. It is expensive and out of the reach of small producers. Cheap low-pressure drip systems were developed for these small-holders by "Netafim" and "Ein Tal" of Israel, "Watermatics" of Mr. Chapin in the USA and Africa, and "IDE International" in the USA and India. Local simplified versions were also developed in other developing countries. "Watermatics" supplies bucket-kits and drum-kits. The bucket kit is comprised of an ordinary bucket, a filter, delivery tubes and two 15-m long drip laterals. The bucket is hung at height of one meter above ground, and the two laterals deliver water by gravity to the garden. The irrigated area is 25 – 30 m2. The bucket-kits cost six dollars each to non-profit organizations and to individual farmers. Super Bucket Kit provides drip irrigation for 10 rows, 10 meters long each, covering 100 m2. This area can be watered from a 250-l container filled once a day.
Fig. 5.3. Bucket kit (left) and drum kit (right) From "IDE International" Brochure "IDE" supplies a five-dollar starter kit that irrigates 25 m2 with one lateral and with two laterals that irrigates 50 m2. A $25 drum kit employs a 200 – 300 l' drum tank for irrigation of 125 m2. The largest version irrigates up to 4000 m2. Shift-capable and simplified systems reduce capital cost by using more labor. Each lateral can be shifted up to ten rows. In the most basic systems, water is emitted from baffled holes or curled micro-tubes, as a substitute to emitters.
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Larger low-cost drip systems for irrigation of 1000 to 10,000 m2 of cotton and other field crops, cost $600-$700/ha. One lateral can irrigate four rows using attached micro-tubes. "Netafim International" developed two gravity-pressurized Family Drip Systems (FDS) models for irrigating 400 m2 of vegetables. Both types include a tank, filter, valves, main line, manifold and laterals. One model has a 50 m long mainline and fifty 7.5 m long lateral tubes suitable for greenhouse or low-tunnel cropping. The second model has a 9 m long main pipe and nine 20 m long lateral tubes on both sides. The tubes are heavy-duty, durable, of smalldiameter, 5–9 mm OD. The system costs $150 per 1,000 m2. Complementary to these systems, a human-powered treadle pump priced at only $30 (compared to $300 for a diesel pump) was developed. There are two treadle pump models: one is powered by walking on two bamboo treadles, while the other is comprised of steel treadles connected to concrete platforms and tubes. The treadles activate two steel pistons that can be manufactured in any local village blacksmith's workshop. Two attitudes prevail regarding simplified drip systems for a disadvantaged smallholder. The first attitude looks for the cheapest equipment and compromises on emission uniformity and durability, assuming that the individual farmer cannot afford high quality products. The other attitude advocates the reduction of system costs by elimination of sophisticated components like automation, fertigation and high level filtration; keeping durability and considerable uniformity of water distribution. The systems are somewhat more expensive than in the first alternative but more cost effective in the long run.
Fig. 5.4. Family Drip System (FDS) Courtesy "Netafim"
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Fig. 5.5. Treadle pump (left – close-up, right – at work) Courtesy "Netafim"
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6. PIPES AND ACCESSORIES Pipes used in micro irrigation are made primarily of Polyethylene (PE) and Polyvinyl Chloride (PVC).
6.1. Polyethylene Pipes The prevalent material, Polyethylene (PE) has four material density categories: 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 g/l and above Carbon black 2% is added to reduce the sensitivity of the pipes to ultraviolet (UV) sun radiation. Another classification relates to the working pressure that the pipe withstands (PN). Common grades of PN used in irrigation are: 2.5, 4, 6, 10, 12.5 and 16 bars (atm). Certain thin-walled laterals withstand lower PN: 0.5 – 2 bar. The pressure tolerance depends on pipe material density and wall thickness. Tolerance data published by the manufacturers relate to temperature of 20 C0. At higher temperatures, the tolerance decreases significantly, hence pipes are tested at twice the designated working pressure and have to withstand three times the working pressure. Plastic pipes are designated according to their external diameter, in mm. In the USA and other countries, pipe diameter is marked in imperial inch units (“). 1” = 25.4 mm. Pipe wall thickness is designated in mm units (in the USA by mil units. Mil = 1/1000 of inch). 1 mil = 0.0254 mm. Laterals are commonly made of LDPE. Delivering and distributing pipes with diameters larger than 32 mm are mostly made of HDPE. Table 6.1. PE (polyethylene) pipes for agriculture PE type LDPE LDPE LDPE LDPE LDPE HDPE HDPE HDPE
ND (Nominal Diameter) 6 mm 4 – 10 mm 12 – 25 mm 12 – 25 mm 16 – 32 mm 32 – 75 mm 40 – 140 mm 75 – 450 mm
Applications Hydraulic command tubing Micro-emitter connection to laterals Thin-wall drip laterals Thick-wall drip laterals Micro and mini emitter laterals Sprinkler laterals Main lines and submains Water supply and delivery networks
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PN - m 40 – 120 40 – 60 5 – 20 25 – 40 40 – 60 40 – 60 40 – 100 60 - 160
Table 6.2. LDPE pipe internal (inner) diameter and wall thickness PN OD ↓
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 16 20 25 32 40 50
9.8 13.2 17.0 21.8 28.8 36.2 45.2
1.1 1.4 1.5 1.6 1.6 1.9 2.4
9.6 12.8 16.6 21.2 27.2 34.0 42.6
1.2 1.6 1.7 1.9 2.4 3.0 3.7
9.2 12.4 15.4 19.4 24.8 31.0 38.8
1.4 1.8 2.3 2.8 3.6 4.5 5.6
8.6 11.6 14.4 18.0 23.2 29.0 36.2
1.7 2.2 2.8 3.5 4.4 5.5 6.9
8.0 10.6 13.2 16.6 21.2 26.6 33.4
2.0 2.7 3.4 4.2 5.4 6.7 8.3
Adapted form Plastro brochure
ND = Nominal Diameter OD = External (Outer) Diameter. In plastic pipes, mostly equivalent to the ND. ID = Internal (inner) Diameter
Table 6.3. HDPE pipe internal (inner) diameter and wall thickness PN OD mm 12 16 20 25 32 40 50 63 75 90 110 125 140 160 180
25 m ID
46.8 59.8 71.2 85.6 104.6 118.8 133.0 152.0 172.2
40 m
Wall thickness
ID
1.6 1.6 1.9 2.2 2.7 3.1 3.5 4.0 4.4
28.8 36.8 46.0 58.2 69.2 83.0 101.6 115.4 129.2 147.6 166.2
60 m
Wall thickness
1.6 1.6 2.0 2.4 2.9 3.5 4.2 4.8 5.4 6.2 6.9
ID
21.8 28.2 35.2 44.0 55.4 66.0 79.2 96.8 110.2 123.4 141.0 158.6
Wall thickness
1.6 1.9 2.4 3.0 3.7 4.7 5.5 6.6 8.1 9.2 10.3 11.8
80 m ID
16.8 21.1 27.2 34.0 42.6 53.6 64.0 76.8 93.8 106.6 119.4 136.4 153.4
Wall thickness
1.6 1.9 2.4 3.0 3.7 4.7 5.5 6.6 8.1 9.2 10.3 11.8 13.3
100 m ID 12.8 16.2 20.4 26.2 32.6 40.8 51.4 61.4 73.6 90.0 102.2 114.6 130.8 147.2
Wall thickness
1.6 1.9 2.3 2.9 3.7 4.6 5.8 6.8 8.2 10.0 11.4 12.7 14.6 16.4
160 m ID 8.6 11.6 15.4 18.0 23.2 29.0 36.2 45.8 54.4 65.4 79.8 90.8 101.6
Wall thickness
1.7 2.2 2.8 3.5 4.4 5.5 6.9 8.6 10.3 12.3 15.1 17.1 19.2
Adapted form "Plastro" brochure
6.2. PVC Pipes PVC (PolyVinyl Chloride) is a rigid polymer. Addition of plasticizers renders flexibility to tubes made of soft PVC. PVC pipes are sensitive to UV sun radiation. Soft and flexible, they are used mainly in gardening and landscape. In agriculture, rigid PVC pipes are mainly used for water delivery and distribution. PVC pipes are installed exclusively underground to avoid damage from UV radiation. Currently, unplasticized PVC (UPVC) pipes are manufactured with improved UV resistance and better tolerance to pressure fluctuations. 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).
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Table 6.4. PVC pipes for agriculture ND
PVC type Soft PVC
6 mm
Soft PVC
Applications
PN - m
Hydraulic command tubing
40 – 80
6 – 10 mm
Micro-emitter connection to laterals
40 – 60
Soft PVC
12 – 25 mm
Tapes and thin-wall drip laterals
5 – 20
Rigid UPVC
½” – 4”
Rigid UPVC
63 – 1000 mm
Risers
40 – 100
Supply networks, main lines, submains
40 – 240
When PVC pipes are installed in heavy or stony soil, it is recommended to pad the trench with sand to prevent damage to the pipe wall by swelling soil and stone pressure. Table 6.5. Rigid PVC pipes internal diameter and wall thickness 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 75 90 110 140 160 225 280 315 355 400 450 500
59.0 70.4 84.4 103.2 131.4 150.2 210.2 262.8 295.6 333.2 375.4 422.4 469.4
2.0 2.3 2.8 3.4 4.3 4.9 6.9 8.6 9.7 10.9 12.3 13.8 15.3
58.2 69.2 83.0 101.6 129.2 147.6 207.8 258.6 290.8 327.8 369.4 415.6 461.8
2.4 2.9 3.5 4.2 5.4 6.2 8.6 10.7 12.1 13.6 15.3 17.2 19.1
57.0 67.8 81.4 99.4 126.6 144.6 203.4 253.2 285.0 321.2 361.8 407.0 452.2
3.0 3.6 4.3 5.3 6.7 7.7 10.8 13.4 15.0 16.9 19.1 21.5 23.9
6.3. Lay-flat Hoses Flexible PVC lay-flat hoses can be used as mainlines and submains. The hose is impregnated with anti-UV radiation protecting agents. When water shuts-down, the hose lies flat on the ground and can be driven over by tractors and other farm machinery. Lay-flat hoses can be positioned on the soil surface or in a shallow trench. These hoses are available in diameters of 75 – 200 mm.
6.4. Fiberglass Pipes In addition to UPVC and HDPE pipes, reinforced fiberglass pipes are used as a substitution for steel and asbestos-cement pipes to deliver water under high pressure from the water source to the irrigated area. 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.
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6.5. 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 designated nominal pipe diameter (ND) is its external diameter. Friction head losses of water flow in the pipe are determined by the internal diameter. It is imperative to check whether the designated diameter is nominal (mostly external) or internal, when using nomograms, on-line calculators and design software.
6.6. Accessories Accessories are classified into four categories: a. Connectors (fittings) b. Control, monitoring and regulation devices c. Chemical injectors and safety devices d. Soil moisture measuring and monitoring instrumentation.
6.6.1. Connectors (Fittings) Connectors are made of metal or plastic materials. They may be two-sided straightthrough or angular units, T or Y shaped triple outlets, four-sided crosses or multioutlet splitters.
Fig, 6.1. Plastic and metal connectors
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Fig.6.2. Start connectors, plugs and lateral ends
Fig. 6.3. Lock fastened connectors
Connectors to control devices are threaded or barbed. Connectors between pipes and laterals are mostly barbed or conic. Simple barb connectors and sophisticated connectors with inner barb and external locking cap are available. HDPE pipes are jointed with locking connectors and may be jointed on-farm by heat fusion. If properly performed, fusion is reliable and durable.
6.6.2. Control Devices Valves are the basic control devices.
6.6.2.1. Gate Valves are used for on-off tasks and are unsuitable for water gradual opening and closing or for flow regulation.
6.6.2.2. Ball Valves are used for on-off tasks. They have low head losses but are unsuitable for flow regulation.
Y valve
Globe valve
Ball valve
Fig. 6.5. Valves
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Fig. 6.4. Connectors and splitters
Hydraulic valve
Metering automatic valve
6.6.2.3. Globe Valves feature precise flow regulation but create relatively high head losses.
6.6.2.4. Angular and Y Shaped Valves are suitable for flow regulation and have lower head losses than globe valves.
6.6.2.5. Butterfly Valves have throttling capability and modest head losses. 6.6.2.6. Hydraulic Valves are manufactured in a variety of models and have a builtin control chamber. Water pressure from the command line actuates a piston or diaphragm that can regulate the flow by narrowing or widening the water passageway of the valve. Functionally, hydraulic valves fall into two categories: Normally Open (N.O.) and Normally Closed (N.C.). a. Normally Open (N.O.) valves stay open until the control chamber is filled with water under system pressure. When the chamber is full, the valve shuts-off. b. Normally Closed (N.C.) valves are kept closed by the water pressure in the mainline. In case of a rupture in the command line, the closure is secured by pressure of a spring. The valve is opened when a tiny valve at the top of the control chamber opens, releasing water from the control chamber into the atmosphere. The pressure exerted by water flowing on the lower face of the diaphragm reopens the valve. Normally Closed (NC) valves create higher head losses, but they are safer to use as the valve remains closed even if the command tube is torn or plugged.
6.6.2.7. Flow Meters are essential for accurate water measurement. Routine biannual check and calibration are required.
Fig 6.6. Hydraulic valve operating principle after Y. Dvir
6.6.2.8. Pressure Regulators are used to maintain a constant downstream pressure independent of upstream pressure fluctuations, provided that the pressure in the inlet is above the designated regulating pressure.
Inline ¾" Low flow 1½" × 2 Fig. 6.7. Pressure regulators Courtesy "Netafim"
2" × 4
33
2" × 6
3" × 10
Pressure regulation is essential in micro irrigation, particularly in drip irrigation. Certain thin wall laterals have a PN of 4 – 15 m, and burst at higher pressure. When using non-compensating drippers, pressure regulators installed on the manifolds or lateral inlets can maintain uniform pressure under harsh topographic conditions.
Table 6.6. Spring actuated pressure regulators Model Flow rate – m3/h Min. Max. ¾" Low flow rate 0.11 3.0 ¾" (One spring) 0.8 5.0 1½" (2 Springs) 1.6 10.0 2"×4 (4 Springs) 3.2 20.0 2"×6 (6 Springs) 4.8 30.0 3"×10 (10 Springs) 8.0 50.0
Mechanical devices regulate the pressure against a spring while in more sophisticated designs pressure is controlled hydraulically by a diaphragm or piston. The metering valve is a combination of a flow meter and hydraulic valve. The desired volume of water to be applied is preset. The valve is opened manually or by command from controller and closes automatically when the assigned water volume has been delivered. Metering valves are used extensively in micro irrigation. They facilitate gradual opening and shutdown of the water, in order to avoid the collapse of thin-walled laterals. They are handily compatible with automation.
Horizontal metering valve
Angular metering valve
Electric valve
Fig. 6.8. Control valves The actuator in the metering valve can be a diaphragm or a piston. A diaphragm is less sensitive to dirt in the water, but prone to tearing and collapse by pressure surges and may wear out due to chemical degradation.
6.6.2.10. Electric Valves Electric valves are commonly used in automation. They are actuated by a solenoid that converts electric pulses into mechanical movement. In small diameters – up to 1” (25 mm) – the solenoid can function as a direct actuator. In greater diameters, the
34
solenoid commands hydraulic actuators. Energy sources are batteries, solar cells and AC current, when applicable.
6.6.2.11. Pressure Relief Valves instantly release water under excess pressure to protect the irrigation system. Two types of valves are available: a. Mechanical valves, working against a spring. b. Hydraulic devices that are more reliable but more expensive.
6.6.2.12. Air Relief Valves Air relief valves and atmospheric vacuum breakers are essential components of micro irrigation systems. Air relief valves release air from the pipelines when they are filled with water and introduce air into pipelines when they are drained on sloppy terrain. Plastic pipes, that withstand pressure of 6, 10 bars and higher can by damaged badly when the pressure falls below atmospheric pressure. “Double action" air relief valves release air from the pipeline, even when the floating device is lifted by pressure buildup as the pipeline is filled with water. Three basic types of air relief valves are available:
6.6.2.12.1. Automatic Valve: releases small volume of air in ordinary operating conditions.
6.6.2.12.2. Kinetic Valve: releases large volume of air while the system is filled with water and allows a substantial volume of air to enter into the system at shutdown. 6.6.2.12.3. Combination Valves: Automatic and kinetic valves mounted together in one assembly.
Automatic
Kinetic
Fig. 6.9. . Air Relief Valves
35
Combination
6.6.2.13. Atmospheric Vacuum Breakers are small devices, ½” – 1” in diameter that break the vacuum at water shutdown and allow air to enter into the system when water drains from the irrigation system and the pipeline pressure falls below atmospheric pressure. Certain types of air relief valves also Fig. 6.10. Atmospheric vacuum breakers introduce air into the irrigation system when pressure equalizes or falls below the atmospheric pressure – functioning as vacuum breakers.
6.6.2.14. Check-Valves and Backflow Preventers When the irrigation system is connected to a potable water supply network, check valves and backflow preventers are used to eliminate backflow of water containing chemicals from the irrigation system to the potable water network.
6.6.2.15. Lateral-End Flush Devices In drip irrigation, the highest amounts of precipitates accumulate in the lateral distal end. Automatic lateral-end flush devices release water at the start of irrigation before the working pressure builds-up in the system. This enables automatic routine flushing of the laterals, eliminating the need for manual flushing.
Fig. 6.11. Lateral-end flushing action
Fig. 6.12. Lateral-end flusher components
36
7. WATER TREATMENT AND FILTRATION Irrigation water quality is defined by its physical, chemical and biological characteristics. The narrow water passageways in drippers and micro-emitters are particularly sensitive to irrigation water quality.
7.1. Physical Quality Parameters: 7.1.1 Suspended solid mineral particles 7.1.2 Organic matter 7.1.3 Live zooplankton
7.2. Chemical Quality Parameters: 7.2.1. Nutrition elements content 7.2.2. Salt content 7.2.3. The concentration of precipitate-forming ions 7.2.4. pH level
7.3. Emitter Clogging Factors 7.3.1. Particulate matter 7.3.2. Biological living organisms and their debris 7.3.3. Chemical precipitates 7.3.4. Combinations of the above mentioned factors Poor system design and management increase dripper clogging. Preventive water treatments against clogging are comprised of sedimentation, filtration and complimentary chemical treatments.
7.3.1. Particulate Matter Micro-emitters are clogged by particles of sand, limestone and other debris too large to pass through the narrow water passageways. Clogging may also occur when small particles stick together to form larger aggregates. Even tiny particles such as suspended clay, which would not cause problems as discrete particles, can initiate clogging if they flocculate to form larger aggregates.
7.3.2. Biological Substances Emitters are clogged by particles of organic matter that block the water passageways. Clogging may be induced by secretions of organisms such as algae and microscopic bacteria. Certain algae are small enough to pass through filters and emitter passageways as discrete entities, but may flocculate in pipelines to form aggregates large enough to clog emitters. Bacteria are small and do not cause clogging; however, they can precipitate compounds of iron, sulfur and other chemical elements that clog the emitters. Some bacteria secrete slime that acts as an adhesive platform for the buildup of clay, algae and other small particles into aggregates. Iron and sulfur bacterial slime is a widespread problem. Iron-precipitating bacteria grow in the dissolved ferrous iron in irrigation water. These bacteria stick to the surface of suspended soil particles and oxidize the dissolved iron. The oxidized iron 37
precipitates as insoluble ferric iron. In this process, a slime called ochre is created, which attaches with other substances in pipelines and clogs the emitters. Specific bacteria that oxidize hydrogen sulfide and convert it into insoluble elemental sulfur, create sulfur slime, a white or yellow stringy deposit formed by oxidation of hydrogen sulfide that is present mainly in shallow wells. The slime clogs emitters either directly, or by acting as an adhesive agent for other small particles.
7.3.3. Chemical Precipitates Chemical clogging of emitters frequently results from precipitation of one or more of the following ions: calcium, iron, magnesium and manganese. These materials may precipitate from the solution and form scales that partially or fully clog emitters. Precipitation can be triggered by changes in pH, temperature, pressure and reaction with ions that are injected into the irrigation water by fertigation as well as by exposure to atmospheric oxygen. Table 7.1. Relative clogging potential of drip irrigation systems by water contaminants Water characteristic Suspended solids (ppm) pH Total dissolved solids (ppm) Manganese (ppm) Iron (ppm) Hydrogen sulfide (ppm) Bacteria population (per ml)
Minor <50 <7.0 <500 <0.1 <0.2 <0.2 <10,000
Moderate 50 -100 7.0-8.0 500-2000 0.1-1.5 0.2-1.5 0.2-2.0 10,000-50,000
Severe >100 >8.0 >2000 >1.5 >1.5 >2.0 >50,000
After Blaine Hanson. 1997
7.4. Water Hardness Water containing substantial concentrations of Ca++, Mg++ and Fe++ is regarded as “hard water”. Hard water is prone to the precipitation of carbonates as low-soluble salts in the irrigation system. Water “hardness” is expressed as a calcium carbonate concentration equivalent in mg/l units. Hardness is calculated by measuring the content of the above mentioned Cations, summing up their concentrations expressed in meq/l and multiplying by 50 (the equivalent weight of calcium carbonate). The most prevalent precipitate from hard water is calcium carbonate. However when fertigating with fertilizers that contain phosphorous and sulfur, calcium phosphate and calcium sulfate (gypsum) may also precipitate. Similar reactions occur with soluble magnesium bi-carbonate.
7.5. Iron and Manganese in Water Iron is often dissolved in groundwater as ferrous bi-carbonate. When exposed to air, the iron is oxidized, precipitates and can plug the emitters. Manganese is occasionally present in irrigation water, but at lower concentrations and with lower activity as a clogging factor than iron.
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7.6. Biochemical Oxygen Demand (BOD) Organic matter suspended in the water is decomposed by microorganisms that consume oxygen along the process. The quantity of oxygen consumed by these organisms in breaking down the waste is designated as the Biochemical Oxygen Demand or BOD. BOD is a consistent indicator for dripper clogging hazard by suspended organic matter. Raw sewage and low-quality reclaimed water have high levels of contamination. Water pumped from ponds, lakes, rivers, streams, canals and dam reservoirs, also contains a high load of impurities. Water pumped from sand aquifers contains great amounts of suspended sand. Sand and silt separation is often performed as a pre-treatment in settling ponds and tanks or by vortex sand separators. For circulated water in greenhouses, slow sand filter systems are used to eliminate water-borne pathogens.
7.7. Filtration Due to the narrow water passageways in micro-emitters and the slow water-flow velocity, micro irrigation systems are susceptible to clogging. As mentioned before, Clogging prevention requires high-level filtration and complimentary chemical and physical water treatments. Table 7.2. Characteristics of water passages in drippers (example) Non-compensated drippers
Flow Rate*
Length
Water passageway Width Depth Cross section mm mm .mm2 1.95 1.84 2.80
Compensated drippers
Flow rate
Length
Inline
l/h 8.0
mm 220
Button
8.0
48
1.39
1.45
Inline
4.1
258
1.35
Button
3.8
50
1.15
Water passageway Width Depth Cross section mm mm mm2 1.39 1.45 2.00
PC button
L/h 8.0
mm 13
2.02
”
4.0
60
1.39
1.49
2.07
1.45
1.95
“
2.0
60
1.25
1.09
1.38
1.05
1.22
Ram PC
3.5
15
1.22
1.22
1.46
Tiran
4.0
95
1.38
1.38
1.90
“
2.3
15
1.04
1.04
1.08
Typhoon
2.8
17
0.81
0.81
0.65
“
1.6
19
1.00
1.00
1.00
Tiran
2.0
135
1.00
1.00
1.00
“
1.2
19
0.91
0.91
0.83
Inline
2.0
280
1.10
1.18
1.30
Midi button PC
4.0
30
1.20
1.25
1.50
Button
2.0
53
0.90
0.80
0.72
“
2.0
32
0.98
1.00
0.98
Typhoon
1.75
20
0.71
0.71
0.5
*In non-compensated drippers – nominal flow rate at 1 bar (10 m) pressure head. Courtesy "Netafim"
7.7.1 Screen (Strainer) Filters Screen filters are designated by filtration degree, filtration surface area and filtration ratio. Filtration degree is designated in microns or mesh number. The filtration degree in microns indicates the diameter of the biggest ball-shaped particle that can pass between the screen wires. The mesh number counts the number of wires along a 1" length of the screen The two concepts are not fully inter-convertible.
39
Perforation width may differ in two screens with the same mesh number due to different wire thickness. Conversion from one system to another is done by rule of thumb: mesh number x microns ≈ 15,000. When selecting the filtration degree, the dimensions of the water passageways in the dripper and the character of water impurities should be considered. When the impurities are suspended inorganic solids (sand, silt, chemical precipitates), the maximum perforation diameter should be 25%-30% of the narrowest dimension (width or depth) in the emitter's water passageway. When the impurities are organic and biological materials, the maximum perforation diameter should not be greater than 10%-20% of the water passageway width. Screen filters are most suitable for water with inorganic impurities, while high loads of organic and biological impurities may clog the screen temporarily.
Fig. 7.1 Screen filter
Courtesy
"Netafim
Fig. 7.2. Head losses in clean screen filters Adapted from "Odis" brochure
One of the main disadvantages of Table 7.3. Screen Perforation Examples screen filters is the rapid accumulation Mesh no. Hole size – microns Wire thickness of dirt on the screen's surface. The microns accumulated dirt increases the head 40 420 250 losses and may trigger collapse of the 50 300 188 screen. Monitoring the pressure 80 177 119 difference between the filter inlet and 100 149 102 outlet is necessary to prevent 120 125 86 excessive dirt accumulation on the 155 100 66 screen. The filter has to be flushed 200 74 53 when the pressure difference between inlet and outlet approaches 0.5 bar (5 m).
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7.7.2. Disc Filters Disc filters are suitable for filtration of water containing mixed, inorganic and organic impurities. The casing is made of metal or plastic materials. The filtering element is a stack of grooved rings, tightened firmly by a screw on cap or by a spring that is compressed by a water-piston. Water is filtered as it flows from the perimeter into the stack inner space through the grooves. The intersections of the grooves provide in-depth filtering. Coarse particles are trapped on the external surface of the stack. Finer particles and organic debris stick to the inner grooves. Disc filters have a higher dirt-retention capacity than screen filters. The definition of the filtration degree is identical to that of screen filters and can be indicated by the color of the discs.
Fig. 7.3. Disc filter
7.7.3. Media Filters
Fig. 7.4. Media filters
41
Media filters protect emitters when using water with a high organic load from open water bodies or reclaimed water. Wide-body (0.5 - 1.25 m in diameter) media containers are made of epoxy-coated carbon steel, stainless steel or fiberglass.
Table 7.4. Sand particle size and mesh equivalent Sand No. Crushed Silica 12 Standard Sand 6/20 Crushed Silica 16 U.S. Silica 80 Crushed Silica 20
Effective sand size – mm 1.1. – 1.2 0.9 – 1.0
Mesh equivalent range 80 - 130 100 - 140
0.6 – 0.7 0.6 – 0.7 0.28
155 - 200 160 - 200 170 - 230
The filtering media are 1.5 - 4 size mm basalt, gravel, crushed granite particles or fine silica sand. The organic impurities adhere to the surface of the media particles. The accumulated dirt should be back-flushed routinely in order to eliminate excessive head losses. The filtration degree is defined equivalently to that of screen and disc filters.
7.7.4. Sand Separators High loads of sand and other solid particles should be removed before getting to the main filtration system. There are two methods for sand separation. The traditional practice is based on sedimentation of solid particles by slowing-down water flow in settling tanks or basins. Closed tanks conserve the water Working pattern pressure while the use of Fig. 7.5 Sand separator open settling basins requires re-pumping of the treated water into the irrigation system. Centrifugal (vortex) sand separators sediment sand and other suspended particles heavier than water by means of the centrifugal force created by tangential flow of water into a conical container. The sand particles thrown against the container walls by the centrifugal force settle down and accumulate in a collecting chamber at the bottom. The collector is washed out manually or automatically. Clean water exits through an outlet at the top of the separator. Each separator has an optimal flow rate range in which the most of the suspended particles are removed without excessive head-losses. At lower flow rates, more sand remains suspended in the water.
42
Fig. 7.6. Hydro-cyclone sand separator – head losses and optimal flow rates From "Odis" brochure
7.7.5. Filter Characteristics 7.7.5.1. Reliability Disc filters are highly reliable. Collapse of the filtration element is uncommon compared to screen filters. In screen filters, the screens are prone to be ripped due to corrosion and to collapse because of pressure fluctuations. The screen-supporting frame must withstand pressure surges.
7.7.5.2. Capacity and Head Losses Water loses pressure as it flows through a filter. The extent of head losses depends on the filter design, filtering degree, flow rate and the degree of dirt accumulation. Normally, for a specific filter type and size, the finer the filtration degree, the lower the nominal discharge. This is due to higher head losses and faster dirt accumulation.
7.7.5.3. Key Screen Filter's Properties: 7.7.5.3.1. Diameter: Designates the water inlet and outlet diameter. 7.7.5.3.2. Filtration Area: The total surface area of the filtration element. The required filtration area for moderately dirty water is 10 - 30 cm2 for each 1 m3/h of flow rate for sprinkler irrigation, 25 - 60 cm2 for micro-jets and 60 - 150 cm2 for drip irrigation.
7.7.5.3.3. Perforation Area: The total open area of perforations. 7.7.5.3.4. Effective Filtration Ratio: The ratio between the perforation area and the filtration area.
7.7.5.3.5. Filter Ratio: The ratio between the perforation area and the inlet crosssection area.
43
The higher the above mentioned parameters, the higher the filter capacity. The nominal capacity of other types of filters is defined according to the permissible head losses. Table 7.5. Nominal filter capacity – examples Make Odis Arkal Arkal Arkal Amiad Amiad Odis Netafim Netafim
Filter type & diameter
Filtration grademicrons 60-400 100-400 75 25 80-300 100-250 60-400 60-200
2” screen 2” disc 2” disc 2” disc 3” screen 3” disc 4” screen 4” gravel 6” sand separator
Capacity m3/h 15-25 25 16 8 50 50 80 60-120 140-230
Nominal filter capacity designates the flow rate at a head loss of 2 m (0.2 bars) in a clean filter. As dirt accumulates, the head loss increases. Filter cleaning is required when head loss amounts to 5 m (0.5 bars). A minimal head loss of 1.5 m (0.15 bar) is required for acceptable sand separation by hydro-cyclone sand separators but the recommended head loss range in these separators is 2.5 - 5 m (0.25 - 0.5 bar). Dirt accumulation capacity is the lowest in screen filters, higher in disc filters and the highest in media (sand and gravel) filters.
7.7.6. Flow Direction The direction of the water flow through the filtration element is an important feature. In disc filters, water flows from the perimeter inwards. This pattern exposes the greater external surface area of the disc stack that is able to retain a much greater quantity of coarse particles than the smaller inner surface area. However, in screen filters, flow from the inside out is more suitable for self-cleaning mechanisms and is less vulnerable to screen collapse by pressure surges. Some models of screen filters have two filtering elements: a preliminary coarse strainer that traps the coarse particles, and a second finer screen for final filtration. Some filter designs include nozzles in the inlet to induce tangential flow of water that drives the dirt to the distal end of the filter where it is flushed-out intermittently or trickles out continuously. In media filters, water enters from the top and exits from the bottom after crossing the filtering media that lies on a perforated plate. Back-flushing is accomplished in the opposite direction – from the bottom upwards. To facilitate proper back-flushing, the media fills no more than 2/3 of the tank volume, so that it can be lifted and agitated during the back-flushing process.
7.7.7. Automatic Flushing and Cleaning Diverse automatic cleaning mechanisms have been developed. Most of them measure the pressure differential and activate the self-cleaning procedure when a preset head differential had built-up. The intervals between flushing events may be controlled by a timer.
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Continuously self-flushing screen filters maintain a flow of filtered water without the build-up of head losses. The dirt is continuously removed from the screen by a tangential, spiraling downward water flow, which flushes the debris into a collecting chamber at the bottom of the casing. The accumulated dirt is drained manually or constantly by a bleeder, or is automatically released when the preset water difference between the water inlet and outlet had been built. The cleaning process is carried on for a preset time length. The cleaning and flushing mechanism is powered by the inherent pressure of the system or by an electric motor. Rotating brushes or sucking nipples clean the screen. For coarse screens, over 200-micron, brushes are sufficiently efficient while for finer screens under 200 microns, cleaning by rotating suckers is more effective. Automatic flushing of disc filters requires release of the discs in the stack. The SpinKleen mechanism combines release of the stack tightening screw, back-flushing by water counter-flow, and spinning of the separated discs by the water stream that flushes the dirt from the grooves through a draining valve that opens automatically.
Fig. 7.7. Automatic flushing of disk filter Adapted from "Arkal" brochure Media filters are flushed automatically by backflow from the bottom that floats the accumulated dirt out through the drain valve on top. The reverse flow automatically begins when the preset pressure differential has been reached. Automatic flushing of media and disc filters requires counter-flow of filtered water. To meet this requirement, filters operate in arrays while the flushing of filters is sequential, one after another.
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Fig. 7.8. High capacity media filter array
Fig. 7.9. Back-flushing of media filters
Fig. 7.10. High capcity automatic filter
Fig. 7.11. Compact automatic filter Fron "Amiad" Brochure
7.7.8. Filter Location Sand settling tanks are installed ahead of the pump while sand separators are installed just downstream of the pump. In highly contaminated water, multi-stage filtration is required. An automatic screen, disc, media filter or a filtration array of several filters should be installed at the pumping site. A backup control screen or disc filters should be installed at the head of each irrigating sector. With moderately contaminated well water, one filtration stage at each sectorial valve may be sufficient.
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7.7.9 Filters for SDI Dedicated disc filters have been developed in which the discs are impregnated with the herbicide Trifluraline. The herbicide is released slowly in low concentration into the irrigation water, preventing root intrusion into the drippers. Effective release lasts for 2-3 years, after which the discs stack should be replaced.
Fig. 7.12. Treflan impregnated disc The discs stack Replacement discs are filter packed in opaque bags, as Treflan (Trifluraline) decomposes quickly when exposed to light.
Courtesy Netafim
7.8. Supplementary Water Treatments In addition to filtration, complementary chemical treatments should be performed on the irrigation water to prevent clogging of micro irrigation systems. Oxidation and acidification are the prevalent complementary treatments. Oxidation decomposes organic matter, prevents formation of slime by sulfur and iron bacteria, blocks development of algae and eliminates infestation by pathogens. Acidification eliminates chemical precipitation and dissolves inherent precipitates in the irrigation system.
7.8.1. Chlorination Chlorine, the common oxidizing agent appears in three forms: a. Solid tablets containing 90% chlorine. b. Liquid sodium hypochlorite (NaOCI) containing 10% chlorine. c. Gaseous chlorine. This form is cheap and efficient but is unsafe in use and commits caution in application. When ferrous iron is present in the water, one ppm (part per million) of chlorine per each ppm of iron is required to kill iron bacteria and precipitate the iron from the water. When hydrogen sulfide is present, 9 ppm of chlorine are needed per each ppm of sulfur to kill the sulfur bacteria, prevent slime growth and precipitate the sulfur from the water. The precipitates formed must be retained by the control filters at the sectorial irrigation control heads to prevent clogging of the emitters. Effective chlorinating decomposes organic materials and blocks the development of algae and plankton present in the laterals and the emitters. 1 - 2 ppm of residual chlorine detected at the distal ends of the laterals indicates adequate chlorination. To maintain these residual levels, chlorine concentrations in the water at the injection
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point should range between 3 – 15 ppm, depending on the impurity load and duration of injection. Levels higher than 15 ppm can harm the diaphragms in certain pressurecompensated emitters and hydraulic valves.
7.8.2. Acidification Acidification of water is required when "hard" water containing a high concentration of bi-carbonates is used for irrigation. The acid injected neutralizes the transient hardness and immerse calcium carbonate precipitates. Acid can be applied with ordinary fertigation equipment or by a dedicated metering pump. The common acidifying agents are sulfuric, nitric, hydrocloric and phosphoric acids. Chlorination of acidified water is more effective than chlorination of alkaline water, reducing the chlorine requirement. Hence if both chlorination and acidification occur simultaneously, acidification will be applied first, followed by chlorination. Mixing acid with chlorinating agents is forbidden since it can induce a toxic chemical reaction. Chemical treatments are implemented upstream from the filtration system. The impurity load is reduced and decomposed material trapped in the filters. The narrower the water passages in the emitters, the greater the need for chemical treatments.
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8. FERTIGATION The combined application of water and fertilizers through the irrigation system increases yields and minimizes environmental pollution caused by excess fertilization. A variety of technologies have been developed for injecting fertilizers into the irrigation system.
8.1. Fertilizer Tank A pressure differential is created by throttling the water flow in the control head and diverting a fraction of the water through a tank containing the fertilizer solution. A gradient of 0.1 – 0.2 bars (1 – 2 m) is required to redirect an adequate stream of water through a connecting tube of 9 – 12 mm diameter. The tank, made of corrosion resistant enamel-coated or galvanized cast iron, stainless steel or fiberglass, has to withstand the network working pressure. The diverted water is mixed with solid soluble or liquid fertilizers. When solid fertilizers are used, the nutrient concentration remains more or less constant, as long as a portion of the solid fertilizer remains in the tank. Once the solid fertilizer had been fully dissolved, continuous dilution by water gradually decreases the concentration of the injected solution. The device is cheap and simple. A wide dilution ratio can be attained with no need for an external source of energy.
Fig. 8.1. Fertilizer tank
From
"Odis" brochure
Drawbacks: nutrient concentration in the irrigation water cannot be precisely regulated. Prior to each application, the tank has to be refilled with fertilizer. Valve throttling generates pressure losses, and the system is not straightforwardly automated.
8.2. Venturi Injector Suction of the fertilizer solution is generated by water flow through a constricted passageway. The high flow velocity of water in the constriction reduces water pressure below the atmospheric pressure so that the fertilizer solution is sucked from an open tank into the constriction through a small diameter tube. Venturi devices are made of corrosion-resistant materials such as copper, brass, plastic and stainless steel. The injection rate depends upon the pressure loss, which ranges from 10% to 75% of the system's pressure and is controlled by the injector type and operating conditions. Venturi devices require excess pressure to allow for the necessary pressure loss. Maintaining a constant pressure in the irrigation
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Fig. 8.2. Venturi injector "Netafim"
Courtesy
system guarantees uniform long-term nutrient concentration. Common head losses are above 33% of the inlet pressure. Double stage Venturi injectors have lower pressure losses downward to 10%. The suction rate depends on the inlet pressure, pressure loss and pipe diameter. It can be adjusted by valves and regulators. Suction rates vary from 0.1 l/h to 2000 l/h. Venturi injectors are installed in-line or on a bypass. In greenhouses, the water flow in the bypass may be boosted by an auxiliary pump. Advantages: cheap open tanks may be used; a wide range of suction rates; simple operation and low wear; easy installation and mobility; compatibility with automation; uniform nutrient concentration; corrosion resistance. Limitations: significant pressure losses; injection rates affected by pressure fluctuations.
8.3. Injection Pumps
Fig. 8.3. Piston (left) and diaphragm (right) hydraulic pumps From "Amiad" Brochure
Fig. 8.4. No-drain hydraulic pump From "Dosatron" brochure
Fertilizer pumps are driven by electricity, internal combustion engines, tractor PTO or hydraulically by the inherent water pressure in the irrigation system.
8.3.1. Hydraulic Pumps are versatile, reliable and feature low operation and maintenance costs. A diaphragm or piston movement injects the fertilizer solution into the irrigation system. Water-driven diaphragm and piston pumps combine precision, reliability and low maintenance costs.
8.3.1.1. Injection Control Hydraulic pumps used in fertigation can be automated. A pulse transmitter is mounted on the pump. The movement of the piston or diaphragm spoke sends electrical signals to the controller that measures the delivered volume. Measurement can also be performed by small fertilizer-meters installed on the injection tube. The controller allocates fertilizer solution according to a preset program. In glasshouses, simultaneous application of a multi-nutrient solution is routine. When the distinct chemical compounds in the fertilizers are incompatible and cannot be combined in a concentrated solution due to the risk of decomposition or precipitation,
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two or three injectors are installed inline one after another, in the control head. The application ratio between the injectors is coordinated by the irrigation controller. In high-income crops grown in glasshouses on detached media, the irrigation water is mixed with fertilizers in a mixing chamber (mixer).
8.3.2. Centrifugal Pumps are used when high capacity is needed or the fertilizer solution is turbid.
Fig. 8.5. Mixer array From "Odis" brochure
8.3.3. Roller Pumps are used for precise injection of small amounts of a nutrient solution. Their life span is relatively short due to corrosion by the injected chemicals.
8.3.4. Electric Pumps Electric pumps are inexpensive and reliable. Operation costs are low and they are readily integrated into automatic systems. A wide selection of pumps is available, from small low-capacity to massive high-capacity pumps. The injection pressure is 1 - 10 bars. Electric piston pumps are exceptionally precise and appropriate for accurate mixing in constant proportions of several stock solutions.
Fig. 8.6. Electric pump
Variable speed motors and variable stroke length allow for a wide range of dosing from 0.5 to 300 L/h. The working pressure is 2 - 10 bars.
8.4. Injection Site Options:
8.4.1. Injection at the Main Control Head - the most convenient and costeffective alternative.
8.4.2. Injection at Submain Heads - a common practice in field crops. 8.4.3. Injection at the Control Head of Each Block – the cost is higher than in the abovementioned alternatives.
8.5. Control and Automation Dosing patterns:
8.5.1. Quantitative Dosing: a measured amount of fertilizer is injected into the irrigation system during each water application. Injection may be initiated and controlled automatically or manually.
8.5.2. Proportional Dosing: maintains a constant predetermined ratio between the irrigation water and the fertilizer solution. Pumps inject the fertilizer solution in a pulsating pattern. Venturi injectors apply the fertilizers continuously and in constant concentration.
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8.6. Avoiding Corrosion Damage Most fertilizer solutions are corrosive. Accessories exposed to the injected solution should be corrosion-resistant. The injection device and irrigation system must be thoroughly flushed after fertilizer injection.
8.7. Backflow Prevention Whenever the irrigation system is connected to a potable water supply network, strict precautions should be taken to avoid backflow of fertilizer containing irrigation water.
8.7.1. Back-siphonage occurs when low pressure in the supply line is created by an excessive hydraulic gradient in undersized pipes in the supply line, a break in the supply line, pump or power failure.
8.7.2. Back-pressure occurs when the pressure in the irrigation system is higher than in the water supply network. This happens when booster pumps are used for irrigation or when the irrigated area is topographically higher than a local water supply tank. An atmospheric vacuum breaker installed beyond the last valve allows air to enter downstream when pressure falls. A pressure vacuum breaker has an atmospheric vent valve that is internally loaded by a spring. This valve is unsuitable for fertigation systems operated by an external source of energy. Vacuum breakers are effective only against back-siphonage and do not prevent back-pressure. A double check valve assembly has two check valves in tandem, loaded by a spring or weight. The device is installed upstream from the injection system and is effective Fig. 8.7. Tandem backflow preventer against backflow caused by both back-pressure and back-siphonage. A reduced pressure backflow preventer consists of two internally loaded check valves separated by a reduced pressure zone. When pressure downstream is higher than the pressure upstream, water is released to the atmosphere and does not flow backwards.
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9. MONITORING AND CONTROL Water and fertilizer can be managed at different levels of monitoring and control. At the basic level, management is based on personal experience, guess-work and intuition without performing actual measurements. In more advanced management levels, soil moisture and nutrient content are monitored, and water and fertilizers are replenished to pre-defined values.
9.1. Monitoring 9.1.1. Soil Moisture Monitoring 9.1.1.1. Tensiometers The tensiometer is the simplest, most widespread mean for monitoring the performance of micro irrigation systems. In on-surface drip irrigation, two units are installed at each monitoring site. The ceramic tip of one tensiometer that is installed within the upper layer, at a depth of 15 – 30 cm in the active aerated root-zone, is used for irrigation timing. The second tensiometer is inserted into the lower limit of the active root zone or the desired wetting depth. Twelve – 24 hours after water application It indicates whether the applied water did indeed replenished the depleted water in the relevant soil volume. A drawback of the tensiometer is its limited range of tension measurement. It does not measure beyond 80 centibars which in certain crops is lower than the irrigation threshold. Above 80 centibars it may dry out and require reactivation.
Fig. 9.1 Tensiometers
Fig. 9.2 Watermark granular sensor
9.1.1.2. Granular Sensors To overcome this discrepancy, new sensors have been developed. Instead of a ceramic tip that is equalized with soil water, a granulated matrix mixed with gypsum encased in stainless steel housing is employed. The measured parameter is the electrical resistance between two electrodes inserted within the matrix. As the soil moisture increases, the resistance decreases. A conversion table translates resistance readings to water potential values. The sensor measures water tension up to 200 centibars.
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Fig. 9.3 Time domain transmissometry sensor
9.1.1.3. TDR and TDT Sensors Other soil water measurement technologies are: Time Domain Reflectometry (TDR) and Time Domain Transmissometry (TDT). Both technologies determine the dielectric permittivity of the soil by measuring the time required for an electromagnetic pulse to propagate along a transmission line within the soil. Since the dielectric constant of water is much higher than that of the soil, higher moisture will increase the permittivity and shorten the time gap between pulse emission and its hit in the target receiver. In TDT, one mode (direction) of the pulse is measured while in TDR the pulse is measured after its reflection to the source. The readings are converted to a percentage of water content in the soil, according to prior calibration. More soil moisture measurement techniques such as gypsum blocks, soil capacitance and neutron probing are rarely used by farmers.
9.1.2. Plant Water State Monitoring 9.1.2.1. Leaf Water Potential Midday leaf water potential indicates the water state of the plant. Measurements are taken at midday. Leaves are cut with their petioles intact. The leaf is then inserted into a pressure chamber (designated pressure bomb). Pressured air is released from a pressurized container into the chamber. A pressure gauge reading is taken when the first drop of sap appears on the petiole tip. The measured value indicates the water potential of the plant. In cotton, midday leaf water potential higher than 20 bars indicates water stress. This measurement technique is suitable for field crops and certain fruit crops
9.1.2.2. Stem Water Potential
The selected leaf
The cut leaf
Fig. 9.4. The pressure bomb From "ICT International" brochure
In some perennial crops the parameter of leaf midday water potential is not a satisfactory indication. In these crops, stem midday water potential is indirectly measured. The leaves for the test are wrapped for two hours with aluminum foil to equalize the leaf and the stem water potentials. The leaves are cut and checked in the abovementioned way. In almonds, stem water potential of 18 – 20 bars is allowed towards harvest but in the stress sensitive phase of fruit set; stem water potential is kept as low as 10 – 12 bars.
9.1.2.3. Trunk Contraction In certain fruit crops such as avocadoes, mangoes and nectarines, daily fluctuations of trunk diameter indicate the water potential of the tree. Measurements are performed by means of dendrometers, using a micrometer to measure the changes between two metallic plates fixed into the trunk on opposite sides.
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9.1.3. Plant Organs Elongation and Expansion In field crops, the rate of inter-node elongation measurement indicates the level of water stress in the plant. In certain fruit crops the rate of fruit expansion is a good indicator of the water state of the tree.
9.2. Irrigation Control 9.2.1. Manual Control Manual opening and closing of valves is the lowest level of control and is rarely used in modern irrigation.
9.2.2. Quantitative Automatic Water Shutdown Valves are opened manually but shutdown is automatic after the preset water amount has been delivered.
9.2.3. Fully Controlled Irrigation Irrigation is regulated by local and central controllers. The controllers are preset to open the valves in the desired time and to close the system when the preset water amount has been delivered. Central controllers can manipulate weather data – rainfall, temperature and evaporation for irrigation scheduling. Weather stations directly deliver data parameters like relative humidity, radiation and wind velocity, by line or cellular communication or the internet, for fine-tuning of the water application.
9.2.4. Integrated Fertigation Control
Irrigation
and
Integrated control of irrigation and fertilizer application is one of the main advantages of automated micro irrigation. In field crops, open field vegetables, and plantations, the controller simultaneously activates the water valves and the fertilizer injectors. In greenhouses, particularly when using detached beds, higher precision is required in synchronizing water and nutrient supply. Fig. 9.5. Fertilizer and water controller For this, dedicated controllers have been from "Gavish" brochure developed to control multi-nutrient supply relying on chemical monitoring of the nutrient solution and drainage.
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9.2.5. Integrated Monitoring and Control The highest level of control integrates monitoring of soil moisture, salinity and pH levels by sensors. All soil moisture sensors described above can be integrated with local or central controllers The central controller receives weather data from weather stations and the Internet. All the data are processed and used to adjust the preset irrigation program. Remote plots can be connected to the central computer by telephone, wireless radio transmitter or Internet. Fig. 9.6. Integrated monitoring and control Coertesy "Netafim"
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10. FLOW RATE - PRESSURE RELATIONSHIP 10.1. Water Pressure Water pressure is a key factor in pressurized irrigation systems performance. Pressure can be expressed in different unit systems. Table 10.1. Pressure and water potential units Definition
Unit
Sub units
Conversion
Pressure/water potential
Bar
=100 Centibars
0.99 Atm.
Pressure/water potential
Atmosphere (Atm)
≈100 Centibars
1.01 Bar
Pressure/water potential
Kilopascal (kPa)
= 1000 Pascal
0.01 Bar=1 Centibar
Pressure/water potential
PSI
Dynamic Head
Meter
≈0.068 Atm. ≈0.68 m =100 cm
0.1 Atm. ~ 0.1 Bar
For simplicity and convenience in irrigation system design, the preferred unit system is the dynamic head, expressed in meters (m) height of water column. This unit system incorporates the effects of topography and friction losses in pipes on the dynamic head, at each point of the irrigation system. Water dynamic head can be referred to as the hydraulic potential energy of the water. The total water head, measured at a specific point of the irrigation system, has three components:
10.1.1. Elevation Head (z) Elevation head is derived from the topographical position, the relative height of a given point above or below a point of reference. For example, if the main valve in the plot is positioned 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 at a point in the water system when no water flow is taking place.
10.1.2. Total Dynamic Head The total dynamic head is the sum of the operating pressure, the friction head losses within the irrigation system and the pumping lift, if applicable. The total dynamic head is a feature of water in flow. In a well-designed irrigation system, the total dynamic head should be the same for each subunit to ensure uniform water distribution in the concurrently irrigated sub-plots.
10.1.3. Velocity Head Flowing water has kinetic energy (velocity head) represented by V2/2g where V is the velocity expressed in m/sec and g is the gravitational constant 9.81 m/sec2. The velocity head can be expressed in m units. Squaring V by itself (V x V = V2) results in units of m2/sec2 which divided by g in m /sec2 units, expresses velocity head in the same units as dynamic head, namely the height of water column in m units.
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10.2. Head Losses Head losses result from friction between the pipe walls and water as it flows through the system. Obstacles - turns, bends, expansions and contractions, etc., along the way, increase head losses. The degree of head losses 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
10.2.1 Friction Losses There are two types of friction losses: Major losses: losses in water flow along straight pipes. Minor (local) losses: created by the flow at bends and transitions. If the flow velocities are high through many bends and transitions in the system, minor losses can build up and become substantial losses. The universal equation used to calculate friction losses of water flow along a pipe is known as the Hazen-Williams equation.
Q J( ‰) = 1.131 × 10 12 × ( )1.852 × D −4.87 C
(Eq. 10.1)
Where: J (‰) = head loss (m per 1000 m length) D = inner pipe diameter (mm) C = friction coefficient (indicates inner pipe wall smoothness, the higher the C coefficient, the lower the head loss). Q = flow rate (m3/h). The Hazen-Williams equation is valid in a limited range of temperature and flow patterns. In small diameter laterals, the Darcy-Weisbach equation gives better results in calculating head losses. Most commonly it takes the following form:
LV 2 Hf = f D2g
(Eq.10.2)
Where: Hf = Headloss – m. f = Darcy-Weisbach friction factor D = Inner pipe diameter – m. L = Pipe length – m. V = Flow velocity – m/sec g = gravitational acceleration (9.81 m/sec2)
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In drip laterals having smooth inner wall surface, the friction factor and the gravitational acceleration can be incorporated in one coefficient and the equation is simplified, correlated with the flow rate and the inner diameter only (Diskin equation).
( 00) = 8.31× 10
J0
7
× Q1.76 × D −4.76
(Eq. 10.3)
Where: J = the friction loss, m per 1000 m of pipe length Q = the flow rate in the pipe, m3/hour D = the inner diameter of the pipe in mm Both the Hazen-Williams and Darcy-Weisbach equations include a parameter for the smoothness of the internal surface of the pipe wall. In Hazen-Williams, it is the dimension-less C coefficient and with Darcy-Weisbach the roughness factor f, expressed in mm. As the C coefficient is higher, head loss will be lower. On the opposite, in the Darcy-Weisbach equation, higher values of f indicate higher headlosses. Table 10.2. Friction Coefficients Pipe material
f - mm (Darcy-Weisbach)
C (Hazen-Williams)
PVC and PE
0.0015 - 0.007
140-150
Asbestos-cement
0.3
130-140
New steel
0.045 – 0.09
110-120
5 year old steel
0.15 – 4.0
80-90
Steel with internal concrete coating
0.3 – 1.0
110-120
Concrete
0.3 – 5.0
90-100
10.2.1.1. Minor (local) Head Losses Minor head losses are expressed as an equivalent length factor that adds a virtual length of straight pipe of the accessory diameter to the length of the pipe under calculation. Particular cases of local pressure losses exist:
10.2.1.1.1. Emitter Disturbance to Water Flow in Lateral On-line drippers are connected to laterals by a barbed or screwed protrusion. These protrusions disturb water flow in the laterals and induce increased head losses. In-line drippers, discrete and integral can also upset the water flow regime in the lateral, generating head losses. The rate of disturb to the flow is designated by the coefficient Kd. The Fig. 10.1. On-line Dripper Connection range of Kd is 0 – 2.00 (and sometimes higher). As this value is higher, head losses increase. The value of Kd depends on the size and nature of the protrusion and the inner cross section of the lateral. The Kd
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of the same dripper will be higher when the internal cross section is smaller. Drip system manufacturers take the Kd into account in calculating the allowed length of laterals.
10.2.1.1.2. Head Losses in Connecting Tubes Microsprinklers, microjets, and multiple outlet drippers utilize small diameter micro tubes of 4 – 8 mm inner diameter for connection between dripper and application point in drippers, and between the lateral and the emitter in micro sprinklers and micro jets. The small cross-section may generate considerable head losses in relatively short tubes of 50 – 100 cm. Drippers have no head loss problem, but in area wetting emitters, a decrease of pressure below the operation pressure may disturb the optimal distribution pattern. To prevent excessive head losses, emitters with a flow rate higher than 30 l/hour will be connected to a lateral with tubes having a minimum inner diameter of 6 mm.
10.2.1.1.3. Head Losses in Valves and Accessories Head losses in accessories are often designated as the losses of equivalent length of a virtual pipe having the same diameter as the accessory. Nomograms of head losses as a function of flow rate appear in commercial brochures and manuals. Certain producers designate a flow factor to valves and similar accessories. This value indicates the flow rate that creates head losses of 1 bar (10 m) while flowing through the accessory. Kv =
Q (Eq. 10.4) (∆p )0.5
Where: Kv – flow factor, m3/hour flow rate with head loss of 1 bar Q – flow rate, m3/hour ∆p – pressure drop, bars
Fig. 10.2. Head losses in hydraulic valves (example)
Example: Kv = 50; What is the head loss when Q = 30 Manipulation of Eq. 10.04: ∆dp = (Q/Kv)2 ∆dp = (30/50)2 = (0.6)2 = 0.36 bar = 3.6 m. 10.2.1.2. Total Dynamic Head The total dynamic head that has to be 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.
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The energy consumed per pumped unit of irrigation water depends on the total dynamic head output of the pump and its pumping efficiency. The total dynamic head depends on: a.
The vertical distance that the water is lifted
b.
The pressure required in the emitters inlets
c.
The friction losses that are created by the water flow from the water source through the pipelines and accessories such as valves and filters. Pumping system efficiency depends upon the pump maintenance level, its power unit effectiveness, and the efficiency of power transmission between them. The power input required by the pump is calculated with the formula below: N=
Q ×H 270 × η
Eq. 10.5
Where: N = required input - HP Q = pump discharge – m3/h H = total dynamic head – m η = pump efficiency – expressed as a decimal fraction
Example: Q = 200m3; H = 150 m; η = 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). This is important in the operation of devices such as Venturi suction injectors.
10.3. Operating Pressure The operating pressure is the pressure required at the emitters to guarantee effective performance and uniform water distribution. The range of the appropriate operating pressure of the emitter is defined and published by the manufacturer in the operating manual. The type of emitter and its operating pressure have to be taken into account in irrigation system design and irrigation scheduling. The design of the distributing pipelines has to ensure the appropriate operating pressure in the emitters. The term ‘working pressure’ (PN) refers to the maximal allowed pressure in a component of the irrigation system (pipe, filter, etc.) that will not result in damage to the component by excessive pressure. There are different procedures for calculation of head losses. In the past, slide rulers and nomograms were routinely used. Nowadays, most system designers use dedicated software and on-line calculators. Head losses in non-distributing pipes differ from head losses in distributing pipes with multiple outlets. When using m (meters) as head units, head loss values are expressed in % or ‰ of length. The actual head losses are obtained by multiplying the percentage/ per-mil value by the pipe length.
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Christiansen friction factor (F) is used to calculate the head losses in pipes with multiple outlets such as distributing mains and submains, manifolds and drip laterals. This factor accounts for the decrease in flow along the lateral and depends upon the number of outlets (N) and the exponent (m = 1.76) of the flow rate (Q) in HazenWilliams equation. The formula to calculate this factor is as follows: F = 1/(m+1) + 1/(2N) +((m-1)0.5/(6N)2)
(Eq. 10.6)
For a lateral with more than 10 emitters, F ≈ 0.40 can be used regardless of the friction loss formula utilized. The head loss due to friction in drip laterals is then determined by:
Table 10.3. Multiple outlets factor F Number. of outlets
F
Where:
1
1.00
Hf is the head loss due to friction in the drip lateral.
5
0.410
Hp is the head loss due to friction of the same flow rate in a non-distributing pipe of the same diameter and length.
10
0.384
Hf = F× ×Hp
(Eq. 10.7)
20 0.373 In dripper laterals where drippers are inserted, molded inside 0.368 or nailed with the stem protruding into the inner cavity of the 40 lateral, the drippers disturb the water flow and increase the 100 0.366 head losses. These additional head losses are designated by Kd – the disturbance coefficient. The values range from zero to 2.0 and higher. When the value is higher, the disturbance to flow and the derived head loss is greater and commits a shorter lateral length.
10.4. Hydraulic Characteristics of Emitters Pressure variations have a different effect on the flow rate of various emitter types. The impact depends on design and construction. The relationship between the operating pressure and the flow rate of the emitter is calculated via the following equation: × Px Q = k×
(Eq. 10.8)
Where: Q = emitter flow rate – l/h k = emitter discharge coefficient – depends on the configuration of the water path in the emitter and the units of pressure and flow rate P = Pressure at the emitter's inlet – m. x = emitter discharge exponent
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The dripper exponent indicates the relationships between the pressure and the flow rate of the emitter. The range of emitter exponents is 0 – 1. Laminar flow drippers have high exponents, in the range of 0.7 – 1.0. Drippers with exponents in the 0.6 – 0.7 range, are considered semi-turbulent. Drippers with turbulent flow have exponents between 0.4 and 0.6. Compensating drippers have exponents that approach zero in the regulated pressure range.
Table 10.4. Effect of dripper exponent on pressure – flow rate relationships Exponent
0.4
0.5
0.6
0.7
0.8
Pressure change - %
Flow rate change - %
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. 10. 3. Relationship between the dripper exponent and lateral length Courtesy “Netafim” The larger the dripper exponent, the more sensitive is the flow rate to pressure variations. A value of 1 means that for each percentage change in pressure there is an identical percentage change in flow rate. An exponent value of 0 (zero) means that the emitter's flow rate is not affected by pressure changes. When laterals are laid above the soil surface, the ambient temperature affects the dripper flow rate. As the water temperature increases, water viscosity decreases and the flow rate of the emitter rises. Lateral heating is more pronounced at the distal ends due to the lower flow velocity. As a result, emitters at the end of the lateral may have a higher flow rate than emitters at the beginning of the lateral. On the opposite, regularly, the flow rate decreases along the lateral due to friction head losses In pressure compensating (PC) drippers, pressure fluctuations above the threshold of the regulating pressure do not affect the flow rate. The regulating pressure is the head range in which regulation of flow rate takes place. The graphs below show that
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in compensating Ram PC drippers, for example, the regulating pressure threshold is about 5 m.
Fig. 10.4. Non-pressure compensating flowpressure relationship
Fig. 10.5. Pressure Compensating dripper flowpressure relationship
10.5. Calculation of Head Losses As mentioned before, slide rulers, tables, nomograms, hand-held and on-line calculators as well as dedicated software can be used to calculate head losses. Manufacturers publish tables and nomograms showing the head losses in their products. Valve producers use the Kv Flow Factor that designates the discharge of the valve in m3/h units at 10 m (1 bar) head loss.
10.6. Technical Data Dripper manufacturers provide detailed technical data in catalogs or on-line, about the flow rate - pressure relationships of their products. These data should be used for determining lateral length and the pressure required at the lateral inlet. Low dripper exponents allow higher pressure differences between drippers, keeping the convention of flow rate difference under 10% between emitters in a simultaneously irrigated area.
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Table 10.5. Example of integral drip laterals technical data EMITTER MODEL
FLOW RATE l/h
DIAMETER mm
- DRIPPER CONSTANTS
DH=7.5%
DH=10%
NOMINAL
INTERNAL
COEFFICIENT
EXPONENT
Pmin-m Pmaxm
Pmin-m Pmaxm
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
16-/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
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
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
20/24/36/44
25-/17/34
Adapted from "Plastro" CD-Rom
This example shows that a large difference in pressure head – up to 20% - is tolerated in drippers with a dripper exponent of 0.5 and below. Manufacturers provide tables indicating the acceptable lateral length in a plateau and designated slopes for a given dripper and lateral combination that keeps the head differences in the allowed range of ± 5% around the average flow rate. Table 10.6. Max. Allowed lateral length for non-compensated line drippers (example)
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Table 10.7. Allowed lateral length for pressure compensated drippers (example)
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11. WATER DISTRIBUTION In drip irrigation, water is applied from point or line sources. Micro-sprinklers and micro-jets wet discrete soil volumes with or without partial overlapping. In on-surface drip irrigation, a small pond is created beneath each emitter. The wetted soil surface area is a small fraction of the total soil surface area in the plot. Water movement within the soil follows a three-dimensional flow pattern, contradicting the onedimensional, vertical percolation pattern typical of flood and full surface coverage sprinkler irrigation. In subsurface drip irrigation, the wetting pattern is quite different: water moves downward, laterally and in some extent, upwards.
Fig. 11.1. Water distribution in the soil: (a) on-surface drip irrigation. (b) SDI Two driving forces affect simultaneously the flow of water in the soil: gravity and capillarity. Gravity drives the water downwards. Capillary forces drive the water in all directions. The equilibrium between these two forces determines the pattern of water distribution within the soil. The wetting pattern affects the distribution of roots in the soil as well as the dispersion and accumulation of dissolved nutrients and salts.
11.1. Soil Wetting Patterns The key factors affecting the distribution pattern of water and solutes in the wetted soil volume with micro irrigation are: a. b. c. d. e. f.
Soil Properties Lateral Placement Emitter Flow Rate Emitter Spacing Water Dosage Chemical Composition of the Water
In fine textured soil, capillary forces are more pronounced than gravity; therefore the horizontal width of the wetted soil volume is greater than its depth. The shape of the wetted volume resembles an onion. In medium textured soils, the wetted volume is
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pear-shaped and in coarse texture, the vertical water movement is more pronounced than the horizontal one so that the wetting volume resembles a carrot. Soil structure also affects water distribution. Compact layers and horizontal stratification increase the horizontal flow of water at the expense of vertical percolation. On the other hand, vertical cracking in compacted soils amplify a preferred downward flow of water followed by incomplete wetting of the upper soil layers.
11.1.2. Lateral Placement a. The maximum diameter wetted by drippers in on-surface drip laterals is just under the soil surface is, namely at depth of 10 – 30. b. The maximum diameter wetted by drippers in sub-surface drip laterals is at the depth of the lateral. In sub-surface drip Irrigation (SDI), the vertical dimension of wetted soil above the emitter in sandy soil is about ¼ of the wetted width. In silt and clay soils this amounts to ½ of the wetted width.
11.1.3. Emitter Flow Rate For the same application time length and the same volume of water: a. A lower flow rate renders a narrower and deeper wetting pattern. b. A higher flow rate renders a wider and shallower wetting pattern. Higher flow rates in on-surface drippers create wider on-surface ponds and a larger horizontal wetted diameter than lower flow rates.
11.1.4. Emitter Spacing For the same application time length and the same volume of water: a. Narrow spacing between drippers on the lateral, renders a narrower and deeper wetting pattern. The width wetted by the drippers increases until adjacent wetted volumes overlap. After the occurrence of overlapping, the majority of the water flow is directed downwards. b. Wide spacing between drippers renders a wider and shallower wetting pattern.
11.1.5. Water Dosage
Fig. 11.2. 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
The wetted volume expands After Bressler 1977 and gets deeper as the amount of applied water increases.
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11.1.6. Chemical Composition of the Water Dissolved chemical compounds in the water may affect the wetting pattern. Detergents and other surfactants contained in reclaimed and storm waters reduce water surface tension and decrease the horizontal flow. The lower surface tension increases the effect of gravity at the expense of the capillary forces, resulting in a narrower and deeper wetted volume.
11.2. Salt Distribution In arid and semi-arid regions, salt accumulation may damage the soil and the crop. Dissolved salts accumulate at the perimeter of the wetted zone, particularly at the soil surface where the water content of the soil is relatively low. A visible saline loop builds up on the soil surface in the margins of the wetted area, along with a shell of salt accumulated at a depth that depends on the leaching efficiency. Appropriate drip irrigation management fully replenishes the water removed by the crop, so that the soil water content remains high enough to address a low concentration of soluble salts. The nutrients applied with the irrigation water follow the same distribution pattern.
Fig. 11.3. Salt distribution in the wetted volume
Fig. 11.4. Leaching of salt into the active root-zone by rain Adapted from Kremmer & Kenig, 1996
Salt accumulated on the soil surface and in the uppermost soil layer commits preventive measures with the first rains after the dry season. Irrigation should be applied as long as the rain lasts, to prevent salts leached from the soil surface to build up in the active root-zone.
11.3. Soil Properties that Affect Water Distribution Patterns Soil characteristics affect the flow of water in the soil and the derived pattern of the wetted zone.
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The equilibrium between the vertical and the horizontal movement in the soil is determined by infiltration and percolation rates that are derived from the soil’s hydraulic conductivity. Hydraulic conductivity is expressed in units of velocity (length/time) m/sec per unit cross section. A given soil type does not have a constant value of hydraulic conductivity. In a specific soil the hydraulic conductivity is greater when the soil is saturated than in an unsaturated state. It also depends on the degree of stratification, the presence of compact soil layers and the moisture content of the soil prior to irrigation. Though different mathematical models have been developed to predict soil water distribution patterns, the use of empirical field techniques to assess the size and volume of the wetted soil is imperative. When plants are irrigated at night when water consumption of the plant is negligible, the volume of the wetted soil depends on the amount of water applied by the dripper and the change in water content of the wetted volume. V = L × [100/(Mf-Mi)]
(Eq. 11.1)
Where: V = Soil wetted volume, l. L = Amount of the applied water, l Mf = the average percentage of water content per unit volume in the wetted zone after irrigation. Mi = the average percentage of soil water content per unit volume of soil prior to the irrigation.
Example 100 l of water were applied at night and the soil water content in the wetted volume increased by 10% per volume. Mf – Mi = 10% V = 100l × (100/10) = 1000l. The wetted volume would be 1000 l (1 m3) of soil.
11.4. Wetting Width and Depth In order to select the optimal dripper and to determine the spacing between laterals and between drippers on the lateral, a thorough assessment of the soil wetting pattern by drippers is highly recommended. A simplified assessment claims that capillary forces drive the flow of water in the soil at the same rate in all directions and gravity pushes the water downward only. The balance between these two forces determines the dimensions of the soil wetted volume and the ratio between the vertical and horizontal axis. During wetting of dry soil, gravity initially drives the water downwards through the empty, non-capillary voids much faster than the lateral capillary movement. As the capillary voids are filled with water, the horizontal flow becomes more pronounced. This happens faster at higher flow rates, therefore the horizontal diameter of the volume wetted by drippers with higher flow rate is larger. In fine textured soil, vertical gravity-driven percolation is relatively slow, faster filling the capillary voids with water.
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11.5. Nutrient Distribution Distribution of nutrients applied by fertigation in the soil depends on the interaction between the nutrition elements and the soil. Potassium ions are absorbed on the surface area of clay minerals and their transport with irrigation water in fine and medium textured soils is limited. The majority of the applied potassium remains in the upper soil layer. In alkaline and neutral soils, phosphorous precipitates from the soil solution with calcium and magnesium as sparsely soluble salts. In acid soils, it precipitates with iron and aluminum and remains in the upper soil layer. Therefore application of phosphorous in deeper soil layers by subsurface drip irrigation (SDI), increases its availability to the root system.
11.6. Root System Development under Drip Irrigation Water application regime and water distribution pattern in the soil affect the root system development and distribution. Each plant family has a typical root dispersal pattern deriving from the growing conditions in the plant’s site of origin and the adaptation of the plant to the local growing environment.
Fig. 11.5. Diverse root systems As depicted in the illustration above, root systems can be shallow or deep, dense, branched or sparse, unrelated to the shape of the plant's canopy. The root system distribution pattern, along with soil properties are key factors in determining dripper spacing and the scheduling of the irrigation regime. Shallow and sparse root systems require dense dripper spacing and frequent water applications. Deep and branched root systems allow wider spacing between emitters and longer time intervals between irrigations.
Fig. 11.6 Typical root systems of field crops
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Frequent and small water applications with 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 winds. On the other hand, due to 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 growing under sprinkler irrigation.
Fig. 11.7. Root system in sprinkler irrigation (left) vs. root system in drip irrigation (right) Courtesy "Netafim"
The active root system and the majority of the root-hairs in drip-irrigated orchard trees, converge in the wetted volume. The highest density of the active roots is in the aerated upper layers, provided there is no accumulation of salts there. At the margins of the wetted volume, where salt accumulates, active roots are sparse. Evergreen fruit trees such as avocadoes 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 coarse textured soils. With SDI, the root distribution pattern differs. Roots are mainly concentrated under and beside the laterals. Very few roots develop above the laterals due to the higher salinity in the upper soil layers.
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12. PLANNING OF MICROIRRIGATION SYSTEMS 12.1. Introduction Setting up a new irrigation system has two phases: a. Planning b. Design Planning is the preliminary stage and consists of collecting data, taking decisions about the irrigation regime, choosing the layout and the components of the system, especially the emitter type and flow rate. The hydraulic design is the next stage and comprises of mapping the irrigation system layout, locating control units, mains and laterals, calculating and determining the pressure-flow regime and programming the operative timetable. This phase can be supported by dedicated computer software provided the programmers have a sound understanding of the fundamentals of hydraulic design.
12.2. Planning Basic pre-design data to be collected: plot boundaries and topography, soil properties, climate data, cropping technology, water-supply capacity and quality, existing equipment. The topographic map of the plot will be scaled to 1:500 (for small plots) – 1:2500 (for large blocks). It will incorporate plot borders, crop spacing, row direction and partition into sub-units, if applicable. Intervals between elevation contours will not exceed 1 m.
12.2.1. Soil Properties a. Soil depth b. Soil texture and structure c. Bulk density d. Saturation Percentage, Field Capacity, Wilting Point e. Infiltration rate and hydraulic conductivity data, if available f. Presence of stratified layers and cracks g. Soil salinity
12.2.2. Climate Data a. Rainfall – amount and seasonal distribution b. Reference Evapo-transpiration (ET0) – calculated from climatic parameters (Penman-Monteith method) or measured in Class A pan.
12.2.3. Cropping Data a. Growth season b. Phenological stages – dates, time-length, foliage coverage, root-zone depth, sensitivity to water stress. c. In-row and between row spacing. d. Peak season Crop coefficient (kc): the ratio between ETc (crop water loss by evapo-transpiration) and the ET0. The crop coefficient kc has been elaborated for use in fully wetted soil surface technologies like sprinkler irrigation. For partial soil surface wetting technologies, the ETc may be adjusted downwards. The component of evaporation from soil surface is significantly reduced due to the small fraction of wetted soil surface. 73
The adjustment can be made using the equation: ETca = ETc × [0.1(GC)0.5]
(Eq. 12.1)
Where: ETca = Adjusted ETc GC = Percentage of ground cover, The percentage of ground cover relates to the shaded soil surface by the crop foliage at midday.
12.2.4. Water Supply Capacity a. Water source characteristics (river, dam, pond, well, public/commercial supply). b. Hours of supply (if by external supplier or due to restrictions on electricity supply) c. Maximum available hourly/daily flow rate (discharge) d. Pump pressure-discharge curve (if applicable). e. Pressure at supply connection (if by external supplier) f. Water quality (physical contamination, hardness, salinity)
12.3. Data Manipulation The capacity of the irrigation system has to correspond with the most demanding crop water requirements, namely peak water consumption by the crop taking place when foliage coverage is maximal, and/or evaporation is in its peak and/or crop sensitivity to water stress is the highest. In the case of annual crop rotation, data relating to the most demanding crop will be taken into account. The optimal irrigation regime of a given plot has to be based on the water consumption by the crop, soil water retention and the irrigation system layout.
12.3.1. Soil Wetting Pattern The partial soil wetting pattern by micro irrigation requires assessment of the percentage of soil volume that is wetted. Diverse models for estimating the wetted volume were developed in which the wetting pattern is determined by: a. Dripper flow rate b. Infiltration rate of the soil (expressed in mm/h) c. Soil hydraulic conductivity (expressed as mm/s). The difficulty with the last two parameters is that the first is not Fig. 12.1.. Wetting patterns by drippers in different constant and decreases in irrigated soil types soil along time. The second parameter is measured in the laboratory on disturbed saturated soil. Frequently, the results of the modeling do not coincide with the actual wetting pattern in undisturbed soil in the field. In drip irrigation, a significant water movement occurs in unsaturated soil, where the equilibrium between gravity and capillary hydraulic forces differs significantly from the equilibrium prevailing in disturbed saturated soil in the laboratory.
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Shani (1987), developed a model for comprehensive design of drip irrigation systems that combines models of water and salt distribution in the soil with models of root development and dispersal in the soil. The hydraulic parameters of the soil are indicated by measuring the radii of the ponded area around drippers, the saturated and residual moisture and the capacity of the capillary space. The advantage of this model is that it enables direct measurement in undisturbed soil - but the final results do not justify the ample work required. Water depletion from the soil is uneven, due to variable root density, unevenness of plant size in the same plot, and soil variability. A customary compromise made in localized irrigation is the estimating the percentage of wetted area. This facilitates use of methodology that had been developed for determining the irrigation regime in full surface wetting technologies, corrected with multiplication by the cover percentage factor.
12.3.1.1. Units of Water Consumption Water depletion and replenishment amounts are expressed in two alternative values: a. mm/day (mm/hour in greenhouses) – designates virtual coverage of the whole surface area in the plot by a uniform water layer of a designated depth in mm. b. m3/ha./day (or inch/acre/day) Conversion formula: (mm/day) × 10 = m3/ha./day.
12.3.2. Manipulation Steps 12.3.2.1. Calculation of the permitted depletion of water from the soil: MAD = (FC – PWP) × BD × Waf × Sd × D × Sl
(Eq. 12.3)
Where: MAD = Management Allowed Depletion - the permitted water deficit – mm = l/m2(×10 = m3/ha) FC = Field Capacity % w/w (weight of water per weight of soil) PWP = Welting Point % w/w FC – WP = Available water % w/w BD = Bulk Density g/ml Waf = Permitted depletion fraction of the available water Sd = Desired wetting depth D = Maximum horizontal wetting diameter Sl = Spacing between laterals
Example: FC = 20% w/w PWP = 15% w/w BD = 1.4 Waf = 0.4 Sl = 1.60 m D = 0.60 m Sd = 0.90 m
Available Water (AW) = 20% - 15% = 5% w/w# Available Water = 5% × 1.4 = 7% v/v## Allowed deficit = 7% × 0.4 = 2.8% v/v Percentage wetted area = 0.60/1.60 = 37.5%* Wetted volume per ha = 10,000 m2 × 0.90 m × 37.5% = 3375 m3 75
Allowed deficit per 3375 × 2.8% = 94.5 m3 = 94.5/10 = 9.45 mm ha. #
w/w = Weight of water per weight of soil v/v = volume of water per volume of soil.
##
12.3.2.2. Assessing the Wetted Volume Assuming full overlapping of the wetted volume by adjacent emitters and ignoring the non-wetted volume due to its bulb shape. The wetted soil volume has no regular geometric shape. Nevertheless, some researchers suggested relating to the wetted volume as an ellipsoid. In that case, wetting depth and the maximum wetted radius can be calculated with the formula: V = 4/3π × a × b × c
(Eq. 12.4)
The definition of the wetted volume by a single dripper is not a simple assignment. It is needed for selecting the dripper type, its flow rate and the operating pressure, spacing between laterals and between drippers, as well as for determining water dosage in irrigation. Due to the difficulties in precise calculation of the wetted volume, data related to wetting volume are only assessments. System designers rely on their experience or rules of thumb regarding wetting diameters that allow a relatively wide range of wetting diameter for each soil class.
Fig. 12.2.Ellipsoid
a. Coarse sand: 20 – 30 cm. b. Fine sand: 30 – 60 cm. c. Loam: 60 – 90 cm. d. Heavy clay: 90 – 120 cm. The diversity is attributed to variability in soil texture and structure in each class. Great variability may be found in the same irrigating block. The best way of estimating wetting volume is on the spot field examination of the chosen emitter in undisturbed soil in the specific plot.
12.3.2.3. Determining the Irrigation Regime When deciding the irrigation regime the allowed deficit should be compared to the crop water requirement. The first step is to calculate the gross daily water replenishment requirement relating to the Irrigation Efficiency of the irrigation system: ETca (Eq. 12.5) W = gr
--------------------
IE Where: Wgr = Gross water requirement - mm/day ETca = Adjusted crop water requirement – mm/day IE = Irrigation Efficiency - % Irrigation Efficiency is defined as:
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IE =
Water beneficially used -------------------------------------------------------------------------------------
× 100
Eq. 12.6
Irrigation water applied Irrigation Efficiency is an arbitrary average value assigned to the irrigation technology. The common values are: a. Border flood irrigation: 50% - 80% b. Furrow irrigation: 70% - 80% c. Sprinkler irrigation: 85% - 90% d. Microsprinklers and microjets: 80% - 90% e. Drip irrigation: 80% - 95%
Example: ETca = 6 mm/d IE = 90%
Wgr = 6/90% ≈ 6.7 mm/d
12.3.2.4. Intervals between Irrigations Calculation of the time interval between applications has to relate to peak demand and stress sensitive phenological phases. The data required for determining the interval: a. Soil water retention – available water. b. Acceptable depletion fraction of available water c. Root-system depth d. Dimensions of the wetted volume or the percentage of wetted area out of the total spacing area. The intervals between applications will be determined by division of the water needed for replenishment of the depleted water by the daily gross water requirement. Wad (Eq. 12.7) TI = Wgr ------------------------
Where: TI = Time interval between irrigations – days Wad = The allowed water depletion – mm = l/m2(×10 = m3/ha) Wgr = Gross water requirement - mm/day
Example: Wad = 9.45 mm Wgr = 6/90% ≈ 6.7 mm/d
TI = 9.45/6.7=1.41 days
In this case, the interval will be the integer value and the water dose will be adjusted respectively. In frequent greenhouse irrigation, intervals are measured in hours. Here, the interval will be 24h ×1.4 ≈ 33 hours.
12.4. Existing Equipment Existence of pumping equipment, delivery and distribution pipelines, accessories, etc. that can be incorporated into the designed system.
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12.5. Planning Crop Irrigation 12.5.1. Orchards Orchards are irrigated by drip irrigation or other micro irrigation technologies. Certain fruit crops benefit from drip irrigation while others are better adapted to spray and micro-sprinkler irrigation. Drip irrigation is the best choice for water saving and salinity handling while microjets and micro sprinklers are favored for frost protection and decreasing Fig. 12.3. Drip irrigation layouts in orchards damage by heat spells, particularly in citrus and other sub-tropical crops.
12.5.1.1. Drip Irrigation There are different types of dripper layouts for orchards. For heavy and medium textured soils, one drip lateral along the row may be sufficient. On sandy and shallow soils, two laterals, 20 – 60 cm apart on each side of the row, perform better. Additional layouts are loops and half circles around the trunk, star and “snake” layouts as shown in figure 12.3. The most explicit water saving in orchards using drip irrigation occurs during the early years prior to fruit bearing. Some types of laterals allow gradual unplugging of the water outlets relating to tree development. In these cases, in the first years only emitters adjacent to the tree are unplugged. In table and wine grapes as well as in kiwi plantations, it is common to hang the laterals 30 cm above ground by fastening them with a clip to the lowest wire on the trellis. Drop concentrators are mounted on the lateral to force the drops to the desired wetting points.
Fig. 12.4. Dripper layouts in wide-spaced orchards For widely spaced orchards such as pecans and nuts spaced 10 × 10 to 15 × 15 m, one lateral per row is insufficient to satisfy the tree's water requirements. Two laterals and more per row, or loops around the trunks, perform better.
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12.5.1.1.1. Nutrition Ditches A new technology had been developed for frequent water application and to "spoonfeed" sensitive crops like mangoes, avocadoes and nectarines in harsh soil and climate conditions. One or two ditches per row, 30 – 50 cm deep and 20 cm wide, are excavated along the tree rows. The ditches are filled with aggregates of volcanic tuff, pumice, gravel or perlite. A drip lateral is laid over each ditch. During the irrigation season, water and nutrients are applied in pulses, several times a day.
12.5.1.2. Micro-sprinkler and Micro-jet Irrigation in Orchards The common layout is one lateral per row. The density of emitters on the lateral depends on spacing between the trees. In densely planted crops, less than 3 m in the row, one emitter between two trees is sufficient. In more spacious planting, one emitter per tree is common. In extremely spacious planting, two emitters per tree are frequently favored.
12.5.2. Micro irrigation in Row Crops The preferred technology is drip irrigation. It is only recently that certain densely grown field crops like potatoes, carrot, onions, etc, are irrigated by micro sprinklers positioned in 6 × 6 – 10 × 10 m spacing. In annual field crops, on-surface drip laterals are laid out at the beginning of the irrigation season and retrieved pre-harvest to avoid damage to the equipment in the harvesting process. Subsurface Drip Irrigation (SDI) is also widely used in irrigation of field-crops. Precise recurring sowing and planting in the same rows every year is obligatory. This is supported by GPS instrumentation with sub-meter accuracy on the farm machinery. For on-surface drip irrigation in field crops, spacing between rows and between plants in the row can vary. Lateral and dripper spacing should conform to crop spacing. Spacing between rows can be modified in order to reduce the number of laterals. For example, instead of uniform 1 m spacing between rows, they are paired at 80 cm within the pair and 1.20 m between adjacent pairs. This allows the installation of one lateral in the middle of each pair, (at 40 cm from each row), instead of one lateral per row and decreases total lateral length in the plot by 50%. With SDI, there are dilemmas regarding the spacing and depth of laterals. For deeprooted crops such as cotton growing on heavy soil, spacing between laterals can be twice the spacing between rows - approximately 2 m. This requires germinating irrigation by a separate irrigation system, such as self-propelled irrigation machines. Innovative approaches are being examined to solve the germination irrigation problem. For crops with shallow root systems, the maximum spacing between laterals is 1 m and installation depth is 30 – 40 cm, which limits tillage options.
12.5.2.1. Drip Irrigation in Cotton Drip irrigation in cotton is applied mainly on shallow soils, small or irregular plots and on steep slopes. In substantial amount area of drip irrigated cotton, on-surface retrievable laterals are laid out after planting and retrieved pre-harvest. Dedicated machinery developed for this technology enables deployment of up to 8 rows at one
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pass. SDI systems are used mainly in heavy compacted soils to avoid using laying/retrieving machinery on wet soil. Since cotton is a non-edible crop and relatively salt-tolerant, substantial areas of cotton are irrigated with low-quality reclaimed and brackish water. Reclaimed water requires high-quality filtration systems and clog-resistant drippers with self dirt release mechanisms.
Fig. 12.5. Mechanized deployment of drip laterals
Fig. 12.6. Cotton root development
From "Naan" brochure
12.5.2.2. Drip Irrigation of Tomatoes for the Processing Industry Drip irrigation is highly advantageous in processing tomatoes. It is well suitable to optimize water and nutrient supply according to climate conditions, phenological stages, yield potential and timing of harvest. It can increase yields and maximize the dry matter and sugar content of the produce. Processing tomatoes are sown with 1.5 – 2 m intervals between rows, and irrigated with one or two laterals per row, depending on soil texture, depth and stratification, SDI installation eliminates the troublesome lateral retrieval under the sprawling plants. Improved quality was also reported with SDI due to better nutrient utilization and elimination of soil surface wetting.
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12.5.2.3. Potatoes
Drip
Irrigation
of
Potatoes are irrigated with one lateral per row laid in a shallow groove on top of the hillock. Burying the lateral 5 – 15 cm deep with small spacing, 10 – 20 cm between drippers along the lateral creates a continuous wetted strip along the row.
Fig. 12.7. Potatoes - Laterals on top of hillocks After Kremmer & Kenig, 1996
12.5.2.4. Drip Irrigation of Corn Corn is highly responsive to drip irrigation. Optimal supply of nutrients in drip irrigation triggers bigger cobs and increased yield. Laterals are laid one per row or between paired rows, depending on soil type.
12.5.2.5. Drip Irrigation of Alfalfa The use of reclaimed water for irrigation of alfalfa requires the use of SDI in order to avoid plant contamination by pathogens. The deep root system of alfalfa allows for spacing of 1 – 1.2 m between laterals, without decrease in yield.
12.5.3. Drip Irrigation of Vegetables Most vegetables grown both in the open field and in protective structures respond positively to drip irrigation and fertigation. Drip irrigation facilitates the adjustment of water and nutrients supply to crop consumption regime. The predominant technology in open field cultures is on-surface seasonallyretrievable drip irrigation. SDI is only seldom installed. Yield decrease in long-term SDI irrigation in certain vegetable species has been reported. Recently, due to difficulties in germination and emergence in SDI, there has been a comeback of traditional on-surface drip irrigation in California, the pioneer of SDI in vegetables.
12.5.3.1. Drip Irrigation of Open-field Tomatoes, Peppers and Eggplants Drip irrigation of the major species of the Solanaceae family is expanding worldwide. Water saving and decrease in fungal diseases compared with sprinkler irrigation, and improved nutrient supply compared with furrow irrigation, result in increased yields. The common layout is one lateral per row or between a closely spaced pair of rows. The soil type determines the spacing between drippers on the lateral which range from 10 cm apart for thin-wall tapes in sandy soils, to 50 cm apart for thick-wall hoses in heavy soils.
12.5.3.2. Drip Irrigation of Strawberries Strawberries are mostly grown on four-row raised beds with plastic mulch in the open field. The spacing between the rows is 20 – 30, and between plants in the rows, 15 – 30 cm. The common layout is one lateral between each pair of rows and spacing of 10 – 30 cm between drippers along the lateral. The laterals are installed beneath the plastic mulch in order to decrease incidences of Botrytis, which is boosted by direct contact of the berries with wet soil.
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12.5.3.3. Drip Irrigation of Cucumbers, Melons and Watermelons The wide spacing between rows (1 – 2 m) in the Cucurbitaceae family results in great water saving during the early growth stages before the full coverage by foliage. The wide spacing reduces the amount of laterals required to cover the plot.
12.5.3.4. Drip Irrigation of Celery Celery is grown on 4 row beds, 1.5 – 2 m wide. Laterals are laid out between each pair of rows. Drippers are spaced 20 – 30 cm apart along the lateral.
12.5.3.5. Drip Irrigation of Cabbage and Lettuce Cabbage and lettuce are grown on 4 row beds, 1.5 – 2 m wide. Laterals are laid in the middle of each pair of rows and the drippers are spaced 20 cm along the lateral.
12.5.3.6. Drip Irrigation of Cauliflower Cauliflower is grown on a double-row bed, 1.2 -1.8 wide. On heavy and medium textured soils, the common layout is one lateral per bed, in the middle of the pair of rows. On sandy soil, one lateral per row is the preferred layout. Dripper spacing along the lateral is 20 – 30 cm.
12.5.4. Drip Irrigation of Protected Crops Protected crops have three levels of protection:
12.5.4.1. Greenhouses and High Tunnels Full height structures enable free passage and utilization of considerable vertical space to optimize the ambient environment. Greenhouses employ two basic types of growing beds: a. Native soil b. Detached media. Full environmental control is gaining momentum in greenhouses. However, in most of them, only irrigation and nutrition are automatically controlled yet.
12.5.4.2. Low Tunnels In low tunnels, a lower degree of control maintained that provides only partial environmental control, but typically, irrigation and plant nutrition are fully controlled.
12.5.4.3. Plastic Mulch The lowest degree of protection, plastic mulch, covers the soil to preserve water, reduce temperature fluctuations within the root-zone and eliminate direct contact of the fruit and foliage with the soil and the irrigation water.
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Fig, 12.8. Wide-scale drip irrigation in greenhouses Courtesy "Netafim" Most of the protected cropping area is irrigated by drip irrigation. For crops grown on native soil, the drip system layout is similar to the systems that are implemented in the open field. The only difference is that protected crops are grown mostly on coarse textured soils that may be imported from an exterior site if the local native soil has a fine texture. Coarser soils require narrower spacing between laterals and drippers as well as shorter intervals between irrigations. When required, the relative humidity within protected structures is increased by spray, fogger or sprinkling emitters. Most of the detached beds have a low water-retention capacity requiring frequent watering and dense layout of laterals and drippers. In pot plants, multi-outlet drippers are used, as well as dedicated drippers such as the arrow dripper. Many of the detached beds contain fully or partially inert materials. Therefore complete fertilization is required including all the 15 plant nutrition elements. Some of these elements cannot be mixed together in their concentrated forms, and 2 – 4 separate fertilizer tanks are required, each with its own injector. More sophisticated systems employ a mixing tank in which 2 – 4 different nutrient solutions are mixed with water and injected into the irrigation system. The nutrient mixture is diluted with water to the final nutrient concentration required and pumped into the irrigation system.
83
Environmentally controlled greenhouses are expensive. Therefore, in order to maximize income, the available space is filled to the maximum: potted plants, propagation beds, grafts and trays for germinating transplants are arranged in several horizontal layers, on separate floors, and one above another. Multi-outlet drippers are the most economical irrigation emitters for this arrangement.
Fig. 12.9. Drip irrigation of potted plants in Greenhouses that recycle drainage greenhouse Courtesy "Netafim" water for reuse in irrigation require a sterilization system to prevent infestation by pests such as fungi, bacteria, nematodes and viruses that may be present in the recirculated water. Sterilization can be achieved with three techniques: a. Ultra violet (UV) irradiation. b. Heating the recycled water to high temperatures. c. Filtering the water with Slow Sand Filters (SSF). All these systems are monitored with and controlled by diverse sensors and computerized controllers.
1.2.5.5. Drip Landscaping
Irrigation
in
Drip irrigation has been adopted for private and public landscaping. Some small-scale private landscape installations use adjustable drippers to facilitate simultaneous irrigation of plants with different water requirements. Adjustable drippers are also useful when plant water requirements change during the irrigation season.
Fig. 12.10. Roadside drip irrigation Courtesy "Netafim"
SDI is used in limited scale on turf and golf courses as well as in sports facilities such as football grounds and tennis courts. Dripper density in turf grounds is much higher than in agriculture. Spacing of 40 – 50 cm between laterals is common in sandy turf and sport grounds with coarse aggregates like volcanic tuff, pumice, gravel and perlite infrastructure. Drip irrigation is the optimal solution for roadside irrigation, along sidewalks and at interchanges. In addition to substantial saving in irrigation water, it eliminates the hazard of wetted roads and walking lanes. When landscape water supply is connected to a drinking-water supply system, installation of backflow preventers is obligatory. In many countries, installation and proper management of backflow preventers is compulsory and enforced by state or local authority regulations.
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13. DESIGN OF MICROIRRIGATION SYSTEMS 13.1. Basic Guidelines 13.1.1. Application Uniformity A fundamental requirement in designing irrigation system is uniform water application in concurrently irrigating blocks that are comprised of the same crop, same age, same phenological phase and the same spacing. Since 100% uniformity in flow rate of emitters is never attainable; by convention, a difference of 10% between maximum and minimum of emitters’ flow rate is acceptable.
13.1.2. Peak Water Consumption The system capacity has to correspond with the crop water requirement. The piping network will enable the coordination of water application to seasonal changes in consumption and to the peak seasonal water consumption.
13.1.3. Durability The chosen components as well as their mode of installation have to guarantee long term durability.
13.1.4. Economic Considerations Economic considerations have to be taken into account in choosing the equipment and the layout. Both the annual return of the initial investment and the long term current annual expenses have to be taken into account.
13.2. The Design Procedure The design process is comprised of several steps.
13.2.1. Choosing Emitter and Layout The preliminary stage of design after the end of the planning phase in which peak daily and hourly water demand had been calculated, time intervals and irrigation dosage had been decided and fertilization regime had been determined, is to choose the emitter and the optimal system layout. The spacing between laterals and between the emitters on the laterals has to correspond with the crop spacing and the water conductivity attributes of the soil.
85
13.2.2. Checking Alternative Layouts When designing irrigation systems, it is imperative to analyze several alternatives, comparing initial investment cost, labor and energy expenses.
1. Comb layout
2. Splitted comb
3. Central fishbone
4. Asymmetric fishbone
5. Splitted fishbone
6. Dual fishbone
Fig. 13.1. Different design layouts Choosing the optimal layout depends on diverse and frequently contradicting considerations. Longer laterals may enable shorter main and submain lines and saving of accessories but oblige the use of larger diameters. The comb layout saves outlets but necessitates larger diameter of the distributing line. Frequently, it is economically favorable to lay manifolds of smaller diameters that reduce the cost of fittings in expense of the additional cost of the manifold piping. Manifolds simplify operation and automation in case of the need to split the plot for separate water applications. 86
The primary phase in the design of the system is the calculation of the head losses created by the water flow. There are diverse procedures for calculating head losses. In the past, designers used tables, slide rulers and nomograms. Dedicated software for irrigation design and on-line calculators replaced those old fashion procedures. Emitter manufacturers indicate the maximum allowed length of drip and other micro-emitter laterals on flat land and in sloping ground, keeping emitters' flow rate variance in laterals within 10% (+/- 5% of the average). The design practice is divided into two phases. In the first phase, head losses are calculated from the distal end to the head of the plot, using nominal values of head and discharge. In the Fig. 13.2. Manifolds save accessories cost second phase, the design is checked and adjusted, going from the head to the distal end. At this stage, the calculation relates to concrete data of discharge and head losses. The map of the plot is divided into sectors and detailed calculations are performed on each pipe segment. The data have to be registered in a design form. Head losses in accessories can be calculated using the concept of equivalent length (see nomogram in page 127). The data manipulated with this concept present head losses in a virtual pipe of the same diameter as that of the accessory. Most manufacturers provide tables and nomograms of the head losses in their products. Local head loss in an accessory can be also calculated, using its flow factor (Kv), if available.
13.2.3. Water Flow Velocity Water flow velocity determines the head losses in the system. As flow velocity increases, the head losses are amplified. In flow velocity over 2.5 m/second, the energy waste due to head losses decreases the economic viability of the system. In mainlines high velocities may trigger water hammer that results in pipe burst. Hence in the preliminary phases of design the expected velocity in manifolds is kept within the range of 2 – 2.5 m/second and in mainlines below 1.5 m/second.
13.2.4. Spacing Spacing between laterals and between emitters on the lateral is determined by the spacing between rows and between plants in the row, Soil depth, its texture and the characteristics of the root system.
13.2.5. Choosing Emitters and Laterals Choosing of the emitter (inline, online, splitted, etc.) and lateral type will relate to the farming technology. The desired durability of the system will determine the options between thick-walled and thin-walled laterals. Topography may affect choosing of pressure compensating or conventional emitters. The chosen emitters and their flow rate will correspond with spacing, planned irrigation regime, soil permeability and the capacity of water supply. Additional
87
considerations are crop response to water distribution patterns and climate control requirements. The actual design is separated into two phases: 1. Layout of laterals and manifolds. 2. Layout of the mainline and the submains.
13.3. Design of Drip Irrigation System for Row Crops In row crops, the layout has to correspond with crop spacing, soil texture and topography.
Example Retrievable drip system for irrigation of maize on flat ground Basic data (manipulated as described in chapter 12) Crop: Maize, length of growing season – 135 days, root system depth – 1 m. Plot dimensions: 420 × 200 m. For harvest convenience, the plot is divided in the middle and row length is 100 in each side. The plot is partitioned to 7 blocks, 60 m wide each. Soil: Sandy loam, Available water – 12% v/v, allowed depletion in peak season – 60%. Topography: 0% slope (flat ground) Spacing: 100 cm between rows, 30 cm between plants in the row Peak season daily gross water requirement: 7 mm Water Source: Reservoir, pumping requested. In sandy loam, the favored choice is 30 cm distance between drippers on lateral (corresponding with plant spacing). In this case it allocates one emitter per each plant.
Firstly, choice of drippers and laterals has to take place. Drawing laterals, 100 m long, to both sides from the middle, represents 333 drippers per lateral. In retrievable on-surface drip irrigation the favored emitter is internal integral dripper that is the least prone to damage during deployment and retrieval of the laterals. Four types of integral drippers can be considered: 1. Pressure compensating dripper in thick-wall lateral 2. Pressure compensating dripper in thin-wall lateral 3. Non-pressure compensating dripper in thick-wall lateral 4. Non-pressure compensating dripper in thin-wall lateral Below are the technical data of the applicable drippers
88
Table 13.1. Compensating dripper (compensating pressure threshold – 4 m) data Model
OD –mm
Wall thickness – mm ID – mm
PN – bars
Kd
16012
16.10
1.2
13.70
4.0
1.6
16010
16.10
1.0
14.10
3.5
1.3
16009
16.10
0.9
14.20
3.0
1.2
OD=Outer diameter, ID=Inner diameter, PN=Working Pressure, Kd=Coefficient of disturbance to flow The above table demonstrates the difference in Kd between model 16012 (wall thickness 12 mm) and model 16009 (wall thickness 9 mm). As the inner diameter is greater, the Kd of a given dripper will be lower. That will enable longer laterals. On the other hand, thicker wall allows for higher working pressure and guarantees longer durability. Table 13.2. Max. lateral length - m Model 16012, ID = 13.70 mm, Inlet pressure 3.0 bars Nominal Spacing between drippers - m flow rate 0.20 0.30 0.40 0.45 0.50 l/h Max. lateral length - m
0.60
0.75
0.90
1.00
1.25
1.50
1.2
104
151
1956
216
237
277
333
386
420
500
575
1.6
86
125
162
179
196
229
276
320
348
415
477
2.3
68
98
127
141
155
181
218
253
275
328
378
3.5
51
75
96
107
118
137
166
193
209
250
288
0.60
0.75
0.90
1.00
1.25
1.50
Table 13.3. Max. lateral length - m Model 16009, ID = 14.20 mm, Inlet pressure 3.0 bars Nominal Spacing between drippers - m flow rate 0.20 0.30 0.40 0.45 0.50 l/h Max. lateral length - m 1.2
118
170
219
242
264
307
368
426
462
548
627
1.6
98
141
181
200
219
255
305
353
383
455
521
2.3
77
111
143
158
173
201
241
279
303
360
413
3.5
58
84
108
120
131
153
184
212
231
274
314
In compensating drippers, the allowed lateral length depends on four factors: 1. The pressure in lateral inlet. As it is higher (in the limits of max. allowed working pressure) the lateral can be longer, ensuring the regulating pressure in its distal end. 2. Dripper flow rate. Higher flow rates dictate shorter laterals. 89
3. Distance between drippers. As it is smaller, lateral length has to be shorter. 4. Inner diameter. Smaller inner diameter commits shorter lateral because of the combination of higher friction head losses and the magnified dripper’s Kd. Table 13.4. Non compensating thick wall dripper pressure – flow rate relationship Nominal flow Pressure - bars rate – l/h 1.00 1.50
2.00
2.50
3.00
Actual flow rate – l/h 1.05
1.05
1.27
1.44
1.60
1.74
1.60
1.60
1.93
2.20
2.44
2.65
2.10
2.10
2.53
2.89
3.20
3.48
4.20
4.20
5.06
5.78
6.40
6.96
8.40
8.40
10.12
11.56
12.81
13.93
Table 13.5. Max. lateral length in non compensating thick wall dripper Model 16012, OD=16.10 mm, Wall thickness=1.20 mm, ID=13.70 mm, PN=4.0 bars, Kd=0.45 Inlet pressure 1.4 bars, Nominal flow rate 1.05 l/h Spacing between drippers - m Slope %
0.20
0.25
0.30
0.40
0.45
0.50
0.60
0.75
0.90
1.00
0.60
0.75
0.90
1.00
Max. lateral length at 10% flow variation - m Inlet pressure 1.4 bars, Nominal flow rate 1.60 l/h Spacing between drippers - m Slope %
0.20
0.25
0.30
0.40
0.45
0.50
Max. lateral length at 10% flow variation - m Uphill
Downhill
-2
49
58
65
77
82
87
95
106
114
119
-1
52
62
71
86
94
100
112
128
142
150
0
56
67
77
96
105
114
130
153
174
187
1
59
71
83
105
116
126
145
173
200
217
2
61
75
87
112
124
135
157
189
220
240
Lateral length of non-compensating drippers is significantly affected by topography. Comparing the same nominal flow rate of 1.6 l/hour in the same lateral diameter indicates that the allowed lateral length with the non-compensating drippers is
90
significantly shorter than in compensating ones. Longer laterals of compensating drippers are allowed since uniform flow rate is kept as far as the head in the lateral is above the regulating pressure. It can be noticed in table 13.5 that Topography affect the allowed length of non compensating laterals while topography impact on compensating drippers’ laterals is less pronounced and hence ignored in the data table. Table 13.6. Non compensating thin wall dripper Nominal flow Pressure - bars rate – l/h 1.10 1.40
1.70
2.00
2.30
Actual flow rate – l/h 1.20
1.25
1.40
1.52
1.64
1.75
2.00
2.09
2.35
2.58
2.79
2.98
2.90
3.03
3.41
3.74
4.04
4.32
Table 13.7. Max. lateral length in non compensating thin wall dripper Model 16320, OD=17.02 mm, Wall thickness=0.81 mm, ID=15.40 mm, PN=2.3 bars, Kd=0.1 Inlet pressure 2.0 bars, Nominal flow rate 1.2 l/h Spacing between drippers - m Slope %
0.2
0.3
0.4
0.5
0.6
0.75
Max. lateral length at 10% flow variation - m Uphill
Downhill
-2
80
101
116
128
139
151
-1
87
113
134
153
169
189
0
95
126
154
178
202
234
1
101
137
170
201
229
273
2
107
148
184
219
251
299
0.4
0.5
0.6
0.75
Inlet pressure 2.0 bars, Nominal flow rate 2.0 l/h Spacing between drippers - m Slope %
0.2
0.3
Max. lateral length at 10% flow variation - m Uphill
Downhill
-2
63
80
92
103
115
125
-1
67
87
104
118
133
151
0
72
96
116
136
154
177
1
75
103
126
151
170
202
2
79
109
135
160
186
220
In thin wall laterals, the increased inner diameter allows for somewhat longer laterals
91
but the restriction on the level of working pressure has the opposite effect.
From the tables above it is comprehended that for 100 m lateral length and 30 cm distance between drippers on lateral, the below presented items are suitable: Table 13.8 the compatible drippers Model
Pressure compensation
Nominal flow rate Working – l/h pressure – bar
Allowed length – m
Ram 16012
Yes
1.2
4
151
Ram 16012
Yes
1.6
4
125
Ram 16012
Yes
2.3
4
98 (marginal)
Ram 16009
Yes
1.2
3
170
Ram 16009
Yes
1.6
3
141
Ram 16009
Yes
2.3
3
111
Tiran 16012
No
1.05
4
102
Typhoon 16320
No
1.2
2.3
126
Typhoon 16320
No
2.0
2.3
96 (marginal)
The final choice depends on preferences, cost and the designer’s past experience. The use of Thicker-walled laterals guarantees longer durability and better pressure surge withstanding. Lower flow rate commits longer irrigation time-length. In calculation of head losses the critical water path had to be considered, namely, from the control head to the distal dripper in the most distant and/or most topographically highest point in the irrigating block.
92
Fig. 13.3. Retrievable drip irrigation system in maize layout
93
Table 13.9. DESIGN FORM COMPENSATING RAM DRIPPER 16012, 1.6 L/H, PRESSURE IN INLRT 30 m a. Flow rate ITEM
UNITS
Dripper
QUANTITY
UNIT FLOW TOTAL FLOW RATE l/h RATE l/h
1
1.6
1.6
Lateral
Drippers
333
1.6
533
Block
Laterals
60
533
31,980
Plot
blocks
14
31,980
447,720
b. Head losses on the way to the critical point Segment
Length – m
Diameter/class Head loss – m Cumulative head demand
E – end point
Minimum required head
10 m*
D-E Lateral
100 m
LDPE** OD 16 5.8 mm, ID 13.6 mm
15.8 m
C-D manifold
30 m
HDPE*** mm
17.4 m
Hydraulic valve
Kv=95
2”
A-C main
490 m
PVC**** 140/6 6.0 mm
25 m
Hydrometer
Kv=135
Globe 4”
27.2 m
50/4 1.6
1.2 m+0.4 m- 19.0 m riser and Tee
2.2
Filter
Pair – 3” Spin- 5.0 ***** kleen filters
32.2 m
Riser, bend and connectors
4”
2.0
34.2 m
7.0
41.2 m
Water lift from reservoir Dynamic head requested in pump
41.2 m
Comments: * Although the compensating (regulating) pressure threshold is 4 m it is advised to design somewhat higher pressure to guarantee drippers’ performance in case of pressure drop in the system. ** Low Density Polyethylene *** High Density Polyethylene **** Polyvinyl chloride ***** The head-loss related to filters is the upper limit of head loss allowed before flushing takes place.
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Pump selection The requested pump will be chosen using the formula: N = Q× ×H/270× ×ή Where: N = Required HP (Horse Power) Q = Pump discharge – (m3/h) H = Total dynamic head – m ή = Pump efficiency (expressed as decimal fraction) N = 64 m3/h × 41.2 m / (270 × 0.75)*** = 2637 / 202 = 13 HP *** Comment: Common pump efficiencies are higher than 75% but along time, efficiency decreases. 75% is regarded as a threshold for refurbishing the pump. This low value is adopted in design to guarantee the long-run appropriate performance of the drip system. c. Equipment list Item
Unit
Quantity
Unit cost Total
The equipment list will include detailed list of all the components of the system, the price and the total cost. It will be used for comparison with alternative layouts. In retrievable drip system, the cost of the device for deployment and retrieval of laterals has to be included. d. Operative schedule The operative schedule will be based on the data collected and elaborated in the planning phase. The schedule will correspond with peak season water requirement.
In this case, the basic data is as follows: Crop: Maize, length of growing season – 135 days, root system depth – 1 m. Plot dimensions: 420 × 200 m. For harvest convenience, the plot is splitted in the middle and row length is 100 in each side. The plot is partitioned to 7 blocks, 60 m wide each. Soil: Sandy loam, Available water – 12% v/v, allowed depletion in peak season – 60% Wetted strip width: 40% of the spacing between rows Topography: 0% slope (flat ground) Spacing: 100 cm between rows, 30 cm in row Peak season daily gross water requirement: 7 mm 1. Allowed depletion: available water × percent of allowed depletion = 12% × 60% = 7.2% v/v
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2. Effective soil water reservoir per Ha: 10,000 m 2 × 1 m. (roots depth) × 40% [(1 m. (raw spacing)] = 4,000 m 3 . 3. Water deficit in the allowed depletion state: 4000 m 3 × 7.2% = 288 m 3 /Ha. This is the water amount needed for replenishment of the deficit. 4. Daily water requirement: 7 mm = 70 m 3 /Ha. 5. The derived interval between water applications: deficit/daily water demand = 288 m 3 / 70 m 3 = 4.11 days. The integer number will be the scheduled time interval. The dose has to be adjusted to the actual interval: 70 m 3 × 4 days = 280 m 3 /ha per application. 6. Number of emitters per Ha: 10,000 m 2 /(1 m × 0.3 m) = 33,333 7. Application rate: 1.6 l/h × 33,333 = 53,333 l = 53.333 m 3 /Ha/h = 5.333 mm/h. 8. Irrigation time-length: 280 m 3 /h/53,333 m 3 /h = 5.25 (5:15) h. Since drip irrigation is not sensitive to wind and evaporation, water application can take place around the clock. It is advised to leave some reserve hours to secure water application in case of electricity blackouts or maintenance requirements. Four turns per day will leave three reserve hours and three turns – 8¼ reserve hours. 9. Time schedule: The plot is partitioned to 14 blocks. If one block is irrigated at a time, four blocks can be irrigated per day and the irrigation cycle will last four days, corresponding with the calculated interval. Since some farming activities have to be performed, although drip irrigation intervene only slightly in these activities, it is better to finish the irrigation in two days, by irrigating two blocks at a time. The irrigation will last two days, leaving two days in the cycle for farming activities. Taking into account these activities, two opposing blocks will be irrigated simultaneously in each application. Alternative Layouts As can be seen in table 13.8, three more choices of non-compensating drippers are feasible. That of the thick-wall laterals commits using dripper of 1.05 l/h that is more prone to clogging due to its narrow water passageway. Additionally, higher pressure has to be applied in order to guarantee acceptable uniformity of distribution. Of the thin-wall laterals, drippers with nominal flow rate of 1.2 and 2.0 l/h can be used. The system will be cheaper but it will last for significant shorter time because of the seasonal deployment and retrieval of laterals. Use of thin-wall (tape) laterals is common for short term use, 1 – 5 years, depending on the wall thickness. In the table below there is example of one of the newest tapes 96
boasting high uniformity. In thin-wall tapes, particularly with short distance between emitters, it is common to designate flow rate to length unit of the lateral and not to the single emitter. In the past, the uniformity requirement from tapes was lower than from thick wall laterals; EU 85% was accepted, compared with 90% in laterals of discrete drippers. In the last years, production improvements facilitated achieving in tapes the same high uniformity as in thick wall laterals. Using these tapes has to be done cautiously. Working pressure is low, 5 – 10 m. That commits the use of pressure regulators. One of these innovative tapes is presented below. It has Cvm (manufacturing coefficient of variation) as low as 2.5% (0.025) and EU of 90% – 94% is attainable. Table 13.10. Thin-wall tape data Emitter spacing – Flow rate – l/m/h cm
Allowed lateral length – m in diverse EU values 94%
92%
90%
20
5.0
93
113
126
30
3.0
132
155
175
40
2.4
163
192
217
60
1.5
221
258
292
The gray row presents a lateral corresponding with the former design example. This dripper can be used, provided no pressure surges will occur and taking into account shorter service duration. Application rate is lower than in the former design. Time length of irrigation in the peak season will be 280 m3 / 30 m3 = 9.6 h, roughly twice than the chosen alternative. The low application rate allows for simultaneous irrigation of four blocks, compared with two blocks only in the former design. Setting up of drip systems commits the installation of air and vacuum vents as well as pressure regulators to prevent pressure surges and water hammer that may burst the laterals. These devices are particularly essential in tapes and other thin wall laterals, due to their low working pressure.
13.3.1. Effect of Topography In the given example, topography can be ignored due to the flat nature of the plot. In case of sloping topography, the hydraulic design has to take into account the effect of topography. If feasible, Mains and submains will deliver water from the higher positions to the lower ones. Manifolds will be laid in sloping land adjacent to the higher edge, asymmetrically splitting the laterals. As far as possible, laterals also will run downward from the higher area to the lower. Use of compensating drippers decreases the complexity of design in harsh topographic conditions. Use of pressure regulators may also facilitate equalizing the pressure in sloping plots. To avoid disturbance to farm activities, distributing pipes and manifolds will be installed when possible, in considerable distance form the growing rows.
97
13.4. Subsurface Drip Irrigation (SDI) Set up of SDI commits the installation of supplementary accessories.
13.4.1. System Flushing System routine flushing is necessary to avoid the accumulation of dirt in laterals and clogging of the drippers. The common practice is the installation of collecting pipes to which the lateral distal ends are connected by manifolds. The valves connecting the manifolds to the collector pipe are intermittently opened manually or automatically for flushing of the laterals.
13.4.2. Contamination by Soil Particles Another nuisance in SDI systems is the suction of soil particles into the drippers by the vacuum created when the water shutdown. To avoid the Fig. 13.4. SDI layout suction, atmospheric vacuum vents have to be installed on the distributing manifold. Additional means that reduce laterals contamination by soil is the use of non-leakage drippers that shut the water outlets on water shutdown.
13.4.3. Root Intrusion Drippers in SDI are prone to clogging by intruding roots. The common counter measure is the application of trifluraline (TreflanTM) that sterilizes the soil adjacent to the dripper. The application can be done in three techniques: a. Injection of the agent into the irrigation system, 2 – 4 times in the irrigation season by means of the fertigation devices. b. Using treflan-impregnated drippers. c. Using treflan-impregnated filtration element. The element is replaced in 1 - 2 years intervals.
13.4.4. Lateral Placement In annuals the recurring sowing/planting precisely above the subsurface laterals is particularly important to guarantee adequate plant development in the early phases of the growing season. For that end GPS equipped machinery has to be used. The depth of installation of the laterals ranges from shallow 5-15 cm in hillocks of 98
potatoes and groundnuts to 35 - 45 cm in cotton. The deeper placement poses difficulties in emergence irrigation but allows for undisturbed land tillage.
13.5. Design of Drip Irrigation in Protected Crops Protected crops are grown in diverse levels of protection. The highest level is in the environmentally controlled greenhouses. Less sophisticated are the ordinary greenhouses and high tunnels, in which only the irrigation and fertilization are automatically controlled. The lowest level is in low tunnels and mulched cropping, where irrigation is operated manually or with a low level of automation. Protected crops are grown on native local soil or on variety of natural and artificial beds. Each combination of bed and control level commits the design of compatible irrigation system. In crops grown on native soil, the design is principally similar to that of design for crops in the open field. Many of the protected crops have dense stand, high value of produce and high sensitivity to water stress. These attributes commit smaller spacing between emitters and shorter time intervals between water applications.
Example Strawberries drip system Strawberries are grown in wide scale in low tunnels or on mulched beds in the open field. The beds arise 15 –30 cm above the walking lanes. Bed width is from 50 cm with one pair of rows to 100 cm with two pairs of rows. Spacing between rows and between plants in the row is 30 cm. Walking lane width is 50 cm. Drip laterals are laid beneath the mulch on the soil surface or buried 5 – 10 cm deep in the soil. In case of one pair per bed, lateral length per hectare is 10,000 m2/1m (distance between bed centers) = 10,000 m. In dual pair bed, the length will be 10,000 m2/ (1.5 m/2) = 13,333 m per
Fig. 13.5. thin-wall non-compensating laterals in strawberries – excessive head losses
99
hectare. Laying and retrieval of the laterals are done more delicately than in field crops. Hence thin wall tapes are suitable. In the example in the former page, 16 mm OD tape had been chosen. The emitters are spaced 30 cm on the lateral; their nominal flow rate is 1.2 l/h. in 10 m water head. Since the drippers are not pressure compensating, their flow rates are significantly affected by the head loss along the lateral. As depicted in the drawing, pressure in lateral drops from 13 m in its start to 10 m in its distal end. That renders flow rate range of 1.2 – 1.35 l/h. The difference of 0.15 l/h from 1.2 l/h is beyond the common acceptable difference of 10%. Moreover, in the manifold of 50/4 mm, the head loss is 2 m. the meaning is that the pressure range in simultaneously irrigating drippers will be 15 – 10 m and the flow rate range will be 1.2 – 1.42 l/h, 15% difference. That discrepancy can be resolved by using manifold of wider diameter, e.g. 63/4 mm. The above example highlights the advantage of using pressure-compensating drippers.
13.6. Design of Irrigation Systems in Greenhouses The wealth of growing beds in greenhouses commits thorough matching of the irrigation system with the combination of crop-bed characteristics. Many growing beds (substrates) have extremely low water retention that commits frequent watering. Crop water consumption is defined per hour and in many cases water is applied several times a day. Irrigation in shallow detached-beds of low water retention, releases considerable amounts of water and nutrients in drainage. In order to eliminate environmental contamination and save the drained water and nutrients, circulation of the drainage is accomplished in many greenhouses. The reuse of the recycled water for irrigation obligates sterilization of the water. Sterilization is achieved either by deep sand filtration, UV irradiation, heating or ozonation. Control of temperature and air relative humidity is essential in sensitive crops grown in greenhouse. Irrigation can be used to moderate extreme, high or low temperatures by the absorption or release of heat from the water. Air relative humidity can be increased by irrigation. Irrigation for climate control commits the installation of misters, foggers or ordinary micro-jets and micro-sprinklers. The irrigation for climate control is applied intermittently in short pulses. Operation is regulated by computerized controllers or by simple timers. Frequently, a dual irrigation system is installed – drippers for irrigation and misters/micro-sprinklers for climate control.
13.7. Irrigation Design in Orchards Orchard irrigation has to comply with fruit trees characteristics: a. Perennial cropping. b. Big plant canopies. c. Deep root systems d. Wide spacing, 3 – 15 m between rows, 1.5 – 10 m in row. e. Sensitivity to extreme weather conditions. 100
These characteristics determine the selection of the irrigation technology. Among the micro irrigation technologies, drip irrigation is favored in saline soils, windy climate as well as in compacted and sloped lands. Micro-jets and microsprinklers are favored in climate sensitive crops as well as in sandy and shallow soils.
13.7.1. Drip Irrigation in Orchards Crops growing in orchards are perennials. The irrigation system has to be durable to avoid of the need of frequent system rehabilitations. The wide spacing in orchards poses the dilemma of how many laterals to install per row. In rows spaced up to 6 m apart, in medium and heavy soils, one lateral per row is satisfactory in most cases. In wider spacing between rows as well as in sandy and shallow lands, two laterals per row is the favored alternative. Another layout in wide-spaced plantations is small circled laterals around the trunk.
Example: Design of drip system in apple orchard: Crop Data Crop: Apple Variety: Golden Delicious Area: 9.6 ha. Partition: 4 blocks, 80 X 300 m, each Topography: 3.5 m slope from NW to SE Spacing: 5 X 4 m Irrigation season: April - October Harvest: Sept. – Oct. Active root depth: 80 cm
Fig. 13.6. Apple orchard – 9.6 Ha
system .
Maximum allowed water depletion: 40% Peak-season average reference evaporation: 8 mm/day Peak-season crop coefficient: 0.9 Soil data Texture: Loamy clay Depth: 1.20 – 1.50 m Bulk Density: 1.4 Field capacity: 32% V/V 101
Permanent Wilting Point: 15% V/V Available Water: 17% V/V Percentage of wetted area by one lateral: 30% Water Supply Data Maximum supply hours: 14 hours a day Maximum available hourly discharge: 100 m3/h EC water: 1.2 dS/m Chloride content: 150 mg/l Calculation of daily Peak Season Water Demand: Daily average evaporation × Crop coefficient = 8 mm × 0.9 = 7.2 mm/day Gross daily demand, assuming application efficiency of 90%: 7.2/90% = 8 mm/d Soil water reservoir volume per ha: Inter row spacing × root system depth × wetted area percentage = 10,000 m × 30% × 0.8 m = 2400 m3 Easily available water soil capacity = resrvoir volume × available water (%)× Allowed deplition (%) = 2400 m3 × 17% × 40% = 163 m3/ha = 16.3 mm Max interval between irrigations = easily available water soil capacity / daily demand = 16.3 mm / 8 mm/day ≈ 2 days Irrigation dose: 8 mm/day × 2 days = 16 mm Two alternatives will be compared: a. On-line non-compensating dripper laterals b. Integral compensating dripper laterals In orchards, the laterals are laid permanently, so, the protrusion from the lateral of on-line drippers, does not disturb. Online drippers can be installed gradually on the lateral. In early years – only 1–2 drippers per tree, adding drippers in correspondence with the root system expansion. On-line drippers have a woodpecker version that facilitates burying the lateral with the drippers underground and emitting the water on the soil surface by-means of micro-tubes.
Firstly the minimum flow rate (mm/hour) has to correspond with the limit of 14 hours of water supply a day. 16 mm/ 14 hours = 1.14 mm/h
102
Non-compensating drippers with flow rate of 4 l/hour render application rate of 0.8 mm/h, not satisfactory yet. Drippers of nominal 8 l/h renders in that spacing application rate of 1.6 mm/h. Application rate of 1.14 l/h can be achieved with drippers of 4 l/h, spaced 70 cm along the lateral.
Fig. 13.7. Non-compensating on-line drippers flow rate pressure relationship
Whenever non-compensating drippers are in use, pressure regulators have to be installed on submains and manifolds in order to equalize as much as possible the pressure in the simultaneously irrigating blocks.
The second checked alternative would be Ram 16 compensating dripper (OD = 16 mm) with flow rate of 3.5 l/h, spaced 60 cm apart on the lateral. In spacing of 5 X 0.6 m, the application rate will be 1.17 mm/hour, somewhat above the minimum requested flow rate. Table 13..2. (Duplicate) Max. lateral length – m. compensating dripper laterals Model 16012, ID = 13.70 mm, Inlet pressure 3.0 bars Nominal Spacing between drippers - m flow rate 0.20 0.30 0.40 0.45 0.50 l/h Max. lateral length - m
0.60
0.75
0.90
1.00
1.25
1.50
1.2
104
151
1956
216
237
277
333
386
420
500
575
1.6
86
125
162
179
196
229
276
320
348
415
477
2.3
68
98
127
141
155
181
218
253
275
328
378
3.5
51
75
96
107
118
137
166
193
209
250
288
103
Diverse layouts are feasible. Two of them will be considered as drawn in the scheme below.
One main, centered
Two submains
Fig. 13.8. Two of the feasible layouts
In the drawing above, two of the feasible layouts are presented. A single mainline in the center, simplifies the design, shortens the main and saves in excavation length in expense of larger pipe diameter. The drawback of this layout is the ascending of the manifolds north to the main. In non-compensating drippers of low operating pressure, 10 – 20 m, the upward flow of the water may create pressure difference beyond the common accepted 20%. Since the exponent of the chosen noncompensating dripper is 0.5, pressure difference higher than 20%, will create flow rate difference higher than 10%. Two submains increase the length of the distributing lines but decrease the differences in flow rate caused by topography. Additionally, the manifolds can be of narrower diameter, compensating for the longer distribution lines. Table 13.11. Basic data Parameter
Unit
Amount
Nominal flow rate
On-line dripper Lateral Drippers distance on lateral Drippers per lateral
Piece m m piece
1 40 0.7 40/0.7 = 57
4 l/10 m head
Number of laterals per block No. of blocks in the plot Irrigation cycle Flow rate per a single day
piece piece day .m3/h
60 8 2
4 l/h × 114 = 230 l/h 14 m3/h 112 m3 112/2 = 56
104
Fig. 13.9. Non- compensating drip system
105
Table 13.12. HEAD LOSSES CALCULATION FORM Segment Flow rate m3/h
Length N.D* H f Outlets FHf – Hz – Total Cumulative factor m m -m .mm/class ** ∆H- ∆H - m *** **** ****** % m
JK lateral
40
16/4
4.2
57
HJ 5.5 manifold
60
40/4
5.5
12
HL 8.5 manifold
90
40/4
15
HL 8.5 manifold
90
50/4
EH 14.0 submain
160
FG lateral
0.23
0.6
0
0.6
0.6
0.36
1.1
0.5
1.1
1.7
18
0.36
4.7
-0.5
4.2
5.9
5
18
0.36
1.5
-0.5
1.0
1
75/4
2
0
1
3.2
-2
1.2
2.2
40
16/4
3.5
57
0.5
0
0.5
2.7
DF 5.5 manifold
60
40/4
5.5
12
0.36
1.2
0.5
1.7
3.4
BD 28 submain
130
75/4
6
0
1
7.8
1
8.8
11.5-12.2
BE mainline
210
90/ 4
2.2
0
1
4.5
1
4
7.4
0.23
28
The gray rows designate alternatives rejected because of unacceptable head losses * ND = Nominal diameter, Class – indicates the working pressure, in bars. ** Hf - % Friction head losses, expressed as meter head per 100 m pipe length. *** F factor – the decimal fraction multiplier of Hf in distributing pipes, ranges from 0.5 for two outlets up to 0.362 for > 100 outlets. Hf = The calculated friction head loss according to the pipe inner diameter, its smoothness, its length and number of outlets. Hz = The effect of topography expressed in m height. Minus sign designates descending slope. Table 13.13. HEAD LOSSES IN THE CONTROL HEAD, flow rate 56 m3/h Component
Diameter
Characteristics
Head-loss - m
Riser
4”- 1 m high
Hydrometer
4”
Kv = 150
1.4
Filter
3” - pair
Back-flush threshold – 5 m
5
0.03
Total
6.4
106
Table 13.14. HEAD LOSSES IN THE HYDRAULIC VALVES ON THE SUBMAINS flow rate 14 m3/h Pressure reducing valve
2”
Kv = 50
0.8 m
Table 13.15. Total requested dynamic head Operation pressure
10 m
Topographic difference (max)
2 m*
Friction head losses in lateral
0.5 m
Friction head losses in manifold
1.5 m
Friction head losses in mainline
7.9 m
Control head
6.4 m
Pressure reducing valves
0.8 m
Total
29.1 m
Comments a. In a cycle of 2 days, blocks a, d, e and h will be irrigated on day 1; blocks b, c, f and g will be irrigated on day 2. In order to equalize the pressure in the simultaneously irrigating blocks, the hydraulic valves on the submains will be of the pressure reducing valves type. b. Laterals of class 4 (not of class 2.5) had been chosen in order to guarantee wall thick enough to fasten the dripper barb for the long run. c. In order to better handle the topographic slope, the submains are not laid in the middle of the blocks but closer to the higher ground. d. Since the actual operating pressure in the drippers will be in the range of 10 – 12 m, the actual flow rate of the blocks will be 5% 10% higher than the designed flow rate that does not affect significantly the pressure regime. Actually, in designing it is taken into account that the average flow is a little bit higher than the nominal.
107
Second alternative – compensating dripper laterals Table 13.16. BASIC DATA Parameter
Unit
Amount
Nominal flow rate
Integral compensating dripper
piece
1
3.5 l/hour
Lateral
m
40
Drippers distance on lateral
m
0.6
Drippers per lateral
piece
40/0.6 = 67
3.5 l/h × 67 = 235 l/h
Number of laterals per block
piece
60
60 × 0.235= 14.1 m3/h
No. of blocks in the plot
Sub plot
8
112.8 m3/h
Irrigation cycle
day
2
Flow rate per a single shift
.m3/h
112.8/2 = 56.4 m3/h
Fig. 13.10. Compensating drip system
108
Table 13.17. Head-loss calculation Segment Flow Length N.D rate -m .mm/class 3 m /h FG Lateral
0.23
H f Outlets Ffactor -%
Hf m
Hz - Total Cumulative m ∆H- ∆H - m m
1.0
0.5
1.5
1.5
-
40
16/4
4.2
67
EF 14 Manifold
150
50/4
8
30
0.36
4.2
0.5
4.7
6.2
BE Mainline
28
240
PVC 110/6
0.9
0
1
2.2
-1.5
0.7
6.9
AB Mainline
56
40
PVC 110/6
2.6
0
1
1
0
1.1
8.0
KL Lateral
0.23
40
16/4
4.2
67
1.0
0.5
1.5
1.5
IK 14 Manifold
150
50/4
8
30
0.35
4.2
1
5.2
6.7
AH Mainline
56
120
PVC 110/6
2.6
0
1
3.1
-0.5
2.6
9.3
CD Lateral
0.23
40
16/4
4.2
67
1.0
0.5
1.5
1.5
BC 14 Manifold
150
50/4
8
30
0.36
4.2
2
6.2
7.7
AB Mainline
56
40
PVC 110/6
2.6
0
1
1
0
1
8.7
JM Lateral
0.23
40
16/4
4.2
67
1.0
0.5
1.5
1.5
HJ 14 Manifold
150
50/4
8
30
0.36
4.2
2
6.2
7.7
AH Mainline
120
PVC 110/6
2.6
0
1
3.1
-0.5
2.6
11.8
56
Table 13.18. Total requested dynamic head Pressure requested in lateral distal end
10 m
Head loss in lateral
1.0 m
Maximum head loss in manifold
4.2 m
Maximum head loss in mainline
3.1 m
Topographic difference
2m
Control head losses
8m
Total
28.15 m
109
Comments a. Using compensating drippers renders more flexibility in design and allows for higher head losses in the distributing system. b. Additional advantage of using compensating drippers is the capability to run longer laterals and save manifolds. This advantage is not presented in the example since in case of use of longer laterals, the manifolds have to be replaced by pipes of larger diameter. c. The major advantage of the compensating dripper is the high level of uniformity in harsh topographic conditions. d. As mentioned before, in coarse textured soils and in shallow lands, two laterals per row are the favored layout. The distance between the two laterals is 80 – 150 cm, depends on the space between the rows and the soil characteristics.
13.8. Design of Micro-jet and Micro-sprinkler Systems in Orchards Micro-jets and micro-sprinklers have flow rates in the range of 20 – 200 l/h. The common layout in orchards is of one lateral per row. In densely planted rows – 2-3 m distance between trees in the row, one emitter can suffice per two trees. Over 3 m space in the row, one emitter per tree is the prevalent layout. In some more spacious plantations with spacing greater than 6 × 6 m, two emitters per tree are frequently installed. The placement of the emitter in the row depends on the shape of the tree canopy. In those crops that the canopy leaves considerable height above soil surface free for water distribution, the emitter is placed in the middle between two trees. In trees that their canopies bend toward the soil surface, converge with each other in the middle between the two trees, the emitter is placed 0.5 – 1 m from the trunk. Like drippers, there are pressure compensating and non-pressure compensating emitters. The choice between micro-sprinklers, micro-jets and ray-jets takes place in respect to spacing, soil type and crop response. In spacious spacing, microsprinklers that wet greater area are favored, in densely planted orchards, micro-jets are more suitable and in heavy and compact soils, prone to run-off, as well as in windy conditions, ray-jets are the best performers.
Example Crop Data Crop: Citrus Variety: Washington Navel Area: 11.5 Ha. Partition: 4 blocks, 80 X 360 m, each Topography: 3.5 m slope from NW to SE Spacing: 6 X 4 m
110
Irrigation season: April - October Harvest: October-December Active root system depth: 100 cm Maximum allowed water depletion: 60%
Peak-season average evaporation: 7 mm/day
reference
Peak-season crop coefficient: 0.7 Soil data Texture: Loamy clay Depth: 1.20 – 1.50 m Bulk Density: 1.4 Field Capacity: 32% V/V Permanent Wilting Point: 15% V/V Available Water: 17% V/V
Fig. 13.11. Citrus grove - 11.5 ha. Table. 13.19. the chosen emitter
Percentage of wetted area: 60% Climate Data
Non regulated (non compensating) Jet sprayer performance data Nozzle color code
Pressure bars
Blue
1.5
55
5.6
2.0
64
5.8
2.5
70
6.0
3.0
77
6.2
1.5
64
6.6
Chloride content: 150 mg/l
2.0
75
7.0
Calculation of daily Peak Season Water Demand
2.5
83
7.2
3.0
91
7.8
1.5
90
8.2
2.0
102
8.6
2.5
115
9.2
3.0
126
9.8
Peak season average daily class A pan evaporation: 8 mm
Flow rate Wetting l/h diameter m
Water Supply Data Maximum supply hours: 20 hours a day Maximum available discharge: 150 m3/h
hourly
EC water: 1.2 dS/m
Daily average evaporation × Crop coefficient = 8 mm × 0.7 = 5.6 mm/day
Green
Red
Gross daily demand, assuming application efficiency of 80%: 5.6/80% = 7 mm/d
111
Soil water reservoir volume per ha: Inter row spacing × root system depth × wetted area percentage = 10,000 m × 60% × 1.00 m = 6000 m3 Easily available water soil capacity = resrvoir volume × available water (%)× Allowed deplition (%) = 6000 m3 × 17% × 60% = 612 m3/ha. = 61.2 mm Max interval between irrigations = easily available water soil capacity / daily demand = 61.2 mm / 7 mm/day = 8.75 days For sake of convenience, the interval will be 7 days and not the allowable maximum. Irrigation dose: 7 mm/day × 7 days = 49 mm. Minimum acceptable application rate: 49 mm/20hours of water supply = 2.45 mm/hour. Minimum emitter flow rate in 4×6 m spacing: 2.45 mm/(4×6)m = 102 l/h Choice of emitter The chosen emitter is non-regulated (non-compensating) jet+ with nominal flow rate of 102 l/h in 20 m head. Table 13.20. Allowed length of laterals
112
Table 13.21. BASIC DATA Parameter
Unit
Amount
Nominal flow rate
Micro-jet
piece
1
102 l/hour
Lateral
m
40
Emitters distance on lateral
m
4
Emitters per lateral
piece
40/4 = 10
102 l/h × 10 = 1.020 l/h
Number of laterals per block
piece
60
61.2 m3
No. of blocks in the plot
unit
8
489.6 m3/h
Irrigation cycle
day
7
Days of irrigation in a cycle
day
4
Flow rate per a single day
.m3/h
489.6 / 4 = 122.4 m3/h
The chosen lateral is the 20/4 mm (20/17 mm OD/ID). It allows for 11 emitters on the lateral, in the range of pressure difference of 7.5% in 1% ascending slope.
113
Fig. 13.12. Micro-jet irrigation system in citrus grove
114
Table 13.22. Head-loss calculation Segment Flow rate m3/h
Length -m
N.D./PN
EF
1.02
40
DE
24
DG
H f Outlets Ffactor -%
Hf m
20/4
13
10
0.35
1.8
0.5
2.3
2.3
72
75/4
4
12
0.35
1.0
1.0
2.0
4.3
36
108
75/4
8
18
0.35
3.0
-1.0
2.0
BD
60
148
PVC 110/6
3.0
0
1.0
4.4
1.0
4.4
8.7
KL
1.02
40
20/4
13
10
0.35
1.8
0.5
2.3
2.3
IK
24
72
75/4
4
12
0.35
1.0
0
1.0
3.3
MN
1.02
40
20/4
13
10
0.35
1.8
0.5
2.3
IM
36
108
75/4
8
18
0.35
3.0
-0.5
2.5
BI
60
388
PVC 110/6
3.0
0
1.0
11.6
-2.0
9.6
15.2
RS
1.02
40
20/4
13
10
0.35
1.8
0.5
2.3
2.3
OR
24
72
75/4
4
12
0.35
1.0
1.0
2.0
4.3
PQ
1.02
40
20/4
13
10
0.35
1.8
0.5
2.3
OP
36
108
75/4
8
18
0.35
3.0
-1.0
2.0
BO
60
228
PVC 110/6
3.0
0
1.0
6.8
0.5
7.3
11.6
UV
1.02
40
20/4
13
10
0.35
1.8
0.5
2.3
2.3
TU
24
72
75/4
4
12
0.35
1.0
1.0
2.0
4.3
WY
1.02
40
20/4
13
10
0.35
1.8
0.5
2.3
TW
36
108
75/4
8
18
0.35
3.0
-1.0
2.0
BT
60
308
PVC 110/6
3.0
0
1.0
9.2
-05
8.7
mm/class
-
Hz - Total Cumulative m ∆H- ∆H - m m
13.0
Table 13.23. Total requested dynamic head Pressure requested in lateral distal end
20 m
Head loss in lateral
1.8 m
Topographic difference
2m
Maximum friction head losses
14.1 m
Control head losses
8m
Total
45.9 m
Comments a. The requested dynamic head relates to the most critical water delivery point.
115
b. The head losses could be decreased by 6 m head by choosing submains of larger diameter – 140/6 mm. But since the water velocity in 110/6 mm pipes is lower than 2 m/sec it is doubtful if the increased pipe diameter is economically sensible. That depends on the cost of energy and has to be considered in respect to local circumstances. c. For sake of minimum head losses, two blocks will be irrigated per day: Day 1: blocks a + e Day 2: blocks b + f Day 3: blocks c + g Day 4: blocks d + h
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14. MAINTENANCE OF MICRO IRRIGATION SYSTEMS 14.1. General The best system design cannot compensate for inadequate system maintenance. Micro irrigation systems in particular, require careful and strict maintenance. The narrow water passageways in the emitters, the widespread use of thin-wall laterals, the sensitivity of the filtration and fertigation devices, the buried underground emitters as well as the complexity of the monitoring and control appliances, require commitment to a meticulous maintenance policy. Maintenance actually begins with system installation. Improper installation will cause trouble throughout the system life span.
14.2. Critical Issues in Installation 14.2.1. PVC Pipes PVC pipes are prone to be damaged by sharp edges of stones or when exposed to expansion and contraction of heavy and compacted soils. Therefore, before laying PVC pipes in a trench, it should be padded with sand. Right angles in the pipeline must be supported by concrete casting to prevent disintegration of the pipeline.
14.2.2. Laterals When connecting laterals to manifolds, the barbed protrusion of the initial connector has to be fully inserted into the lateral to prevent the connectors from popping out in pressure surges.
Fig. 14.1. Punch (left) and holder (right) Courtesy "Netafim" Laterals laid from reels, have to be positioned leveled on the ground for several hours before they are connected and stabilized. The delay is necessary to accommodate the lateral and release twisting formed in the reel package.
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Precise punching of holes in the lateral for insertion of on-line drippers and feeder tubes of micro-jets and micro-sprinklers, requires dedicated tools, as shown in fig. 14.1. Before initializing the system, laterals, manifolds and pipelines have to be thoroughly flushed, to wash out all debris and soil particles that penetrated into the system during installation work. In plots prone to woodpecker activity, subsurface drip irrigation is the preferred alternative; otherwise, woodpecker drippers can be installed.
14.3. Routine Inspection Routine inspections and preventive measures are necessary to guarantee appropriate performance of the micro irrigation system. The best maintenance policy is to inspect the whole system periodically and systematically. Time intervals between inspections depend on water quality and the attributes of the system components. Inspections can be performed weekly, monthly, or twice a year in favorable conditions.
14.3.1. Pump Inspection In self-pumping installations, pump efficiency has to be tested once in 5 years. When water contains sand particles and/or the water is corrosive, the test should be performed bi-annually. Pump efficiency below 75% is economically undesirable in contemporary high energy costs. Low efficiency may indicate the deterioration of pump components that if are not repaired or replaced promptly, may terminate pumping.
14.3.2. System Performance Comparing the system’s designed discharge to the actual flow rate provides preliminary indication of system performance. Deviation up to ±10% is normal. A flow rate that is significantly lower than the designed discharge may indicate partial plugging of emitters or chocking of filters by dirt accumulation. A flow rate significantly higher than the designed may indicate burst pipelines or punching of pipes and laterals and water leakage. Deviation from the designed flow rate can also indicate changes in the pressure regime. The first step is to check the hourly flow rate at the main flow meter and compare it with the designed flow rate (number of emitters multiplied by the emitter’s nominal flow rate). Second step - the pressure gauges that are installed in the plot have to be checked. The measured values have to be compared to the designed pressure for each set. The pressure difference between inlet and outlet and dirt accumulation in filters have to be checked as well. When low flow rate is noticed in an appropriate pressure regime, on-farm inspection of emitter flow rate uniformity should be performed. The minimum number of emitters per sample is 20. The recommended number is 40-50. Once measured, the EU can be calculated and if it is unacceptable, the emitters should be cleaned with acid, flushed with pressurized air or replaced. The system should be checked again after treatment.
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Visual indicators of inadequate system performance are random stressed plants, surface runoff, “surfacing” in SDI and white salt spots on the soil surface.
14.4 Routine Maintenance 14.4.1. System Flushing and Cleaning During irrigation, dirt, chemical precipitates and organic matter accumulate in the irrigation system. Most of the dirt accumulates in the distal ends of laterals, manifolds and pipelines. Before the first irrigation in the season, the system has to be flushed thoroughly. For proper dirt removal, flushing of laterals has to be sequential, one after another, to keep the appropriate pressure needed for Fig. 14.2. Automatic lateral end flushing valve adequate flow velocity in the open distal Courtesy "Netafim" end. The lateral end stopper is released and the dirty water is allowed to exit until clean water appears. Lateral flushing can be accomplished automatically by automatic flushing valves. In this case, flushing takes place in the initiation of the irrigation between water opening and the build-up of the operating pressure inside the lateral. Flushing velocities should be at least 0.5 to 0.6 m/s in order to remove effectively the dirt from the laterals. Flushing has to be performed several times per season. Intervals between flushing events depend on the rate of dirt accumulation.
14.4.2. Cleaning of Plugged Drippers When routine flushing is not sufficient to guarantee uniform emission, more drastic measures are required. Flushing with acid solution can dissolve lime and gypsum precipitates. Sulfuric, hydrochloric, phosphoric and nitric acids are used. The latter is the most potent agent but the most unsafe to use. Acids necessitate strict cautionary measures. In the case of unsuccessful acid treatment, the system can be flushed with high-pressure compressed air. Immersing the reels of retrieved laterals in an acidic solution for a few hours yields better results than flushing in the field. Sometimes, pressing the dripper carefully in a dry state can shatter the solid precipitates and enable them to be flushed out of the lateral. In certain compensating drippers, diaphragms lose their flexibility with time. Some diaphragms are sensitive to high concentrations of oxidizing agents like chlorine and bromine compounds.
14.4.3. Maintenance of Micro-jets and Micro-sprinklers In distinction from drippers, malfunction of micro-jets and micro-sprinklers is easily noticed. The visual indications are changes in distribution patterns, an altered rotation rate in rotating emitters, stuck immobilized rotating and vibrating emitters and slanted stakes. Emitter-bearing stakes have to be positioned vertically. Stake bending impairs water distribution and may enhance run-off and water losses. 119
Certain stakes are marked to indicate the depth of insertion required to stabilize the emitter vertically and to ensure the emitter's right height above soil surface for optimal water distribution.
14.4.4. Maintenance of Accessories The working environment of an irrigation system can be considered “hostile”. Chemical precipitations, friction-induced wear, corrosion and mucous excretions by microorganisms cooperate to hamper system performance. In the framework of routine maintenance, the functioning level of discrete components has to be checked routinely. Flow meters have to be calibrated once in 2–5 years, depending on the volume of water delivered and concentration of solid contaminants in the water. Most hydraulic valves have an internal diaphragm. The integrity and flexibility of the diaphragm has to be routinely inspected. If necessary, the diaphragm should be replaced. Pressure regulators operation mechanism is based on spring resistance or hydraulic equilibrium maintenance. Springs are weakened after prolonged operation. They should be inspected once in two years and replaced if necessary. Vacuum-relief valves carry out an important function in drip irrigation systems, particularly in sub-surface systems. When the irrigation is turned-off, water remaining in the system flows downhill to the lowest outlets. The water vacating the high points creates a vacuum, which causes the emitters in this Fig 14.3 Vertical section of the plot to suck in air and dirt. In extreme cases, stake PVC mainlines and thin-wall laterals may collapse. Vacuumrelief valves, installed at the high points in the system, are prone to clogging and need periodic inspection to ensure that no solid objects are caught inside and that they are not caught in an open or shut position. Air release valves also require the same periodic examination. The filtration system should be thoroughly inspected. In some filter types, the steel body is coated with epoxy paint to protect it from corrosion. The epoxy paint should be checked routinely. Cracks in the coating shorten the endurance of the entire body. The collectors of sand separators, should be purged periodically, otherwise excess accumulated sand will lower separation efficiency. Screen filters should be opened and screens visually inspected for wear, tear and blockage by organic matter, silt and chemical precipitates. The same applies to disk filters. Manually cleaned filters will be serviced when the pressure difference between the inlet and outlet exceeds 5 m. Automatic back-flushing filter systems require periodic visual inspection of the filtering elements against wear and presence of persistent contaminates. Backflushing filter components: control hydraulic valves, solenoids and rotating brushes or vacuum suckers, may require periodic servicing and lubrication. Most of them include
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a small water filter to prevent blockage of solenoid ports and valve control chambers. This filter needs frequent manual cleaning. Automatic back-flushing media filters require special attention. They fluidize and resettle the filtering media with every flushing cycle. The discharge of back flushed media filters should be within the specified range of each model. For a typical 48" diameter tank, the range is 70 - 95 m3/h, higher than the filtering capacity of 50 – 70 m3. Below the lower margin, contaminants tend to infiltrate deeper into the media bed. Flow rates higher than the recommended upper threshold can lead to coning and canalization of the filtering media. To effectively back-flush a filter, an adequate flow rate is critical particularly for sand filtering media. It should be large enough to fluidize and lift the filtering media, while pushing out just only a minor amount of sand through the flushing discharge manifold. Media filters must be routinely inspected to check the height of the filtering media in the tank. During the back-flushing process, a portion of the media is drained-off. When the void tank volume is greater than ⅓ of the total volume, the missing media should be replenished.
14.4.5. Maintenance of Fertigation systems 14.4.5.1. Evaluating System Performance Excessive fertilization can induce salinity damage as well as antagonistic interference between nutrition elements. The precision of nutrient application can be checked in four procedures: a. Collecting water samples from the dripper laterals downstream from the injection point, and comparing the sample analysis with the desired concentration. b. Analyzing an extracted soil solution. c. Analyzing the nutrient content of soil samples. d. In detached beds it is common to collect drainage samples and compare them with samples of water collected from emitters. If the nutrient concentration of the drainage samples is significantly lower than the dripper’s emitted solution, the rate of the injected nutrients should be increased. The likelihood of leaching nutrients by excess water should also be examined. If nutrient level in drainage is higher than in the dripper emission, there may be excess nutrient injection or deficit in water application.
14.4.5.2. Maintenance of Chemical Injection Devices The fertigation equipment is exposed to corrosive nutrient solutions. Metallic components like epoxy coated fertilizer tanks, injection pump components, controlling valves and pressure gauges corrode and should be replaced frequently. Some injection pumps have to be lubricated periodically. In diaphragm fertilizer pumps the diaphragm should be inspected for integrity and flexibility. Inflexible diaphragms will not perform perfectly.
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14.5. Chemical Water Treatments Chemical water treatments keep the system clean and running. They can be applied as a preventive measure or as a corrective treatment after the clogging occurred. The treatments can be classified into three groups: a. Acidification b. Oxidation c. Sterilization
14.5.1. Acidification Acidification lowers water pH. This eliminates precipitation of insoluble salts of the cations calcium, magnesium, Iron and manganese with the anions bi-carbonate, carbonate, sulfate and phosphate. In low pH levels, the solubility of these salts is relatively high and the rate of precipitation is reduced significantly. The required concentration of the acid in irrigation water for attaining satisfactory results depends on the levels of bi-carbonates and sulfates in the water. The customary range is 0.5% - 1.5% in continuous acidification.
14.5.2. Oxidation The dominating oxidizing agents are diverse chlorine compounds. Oxidation is implemented for decomposing of sustained organic matter and preventing development of algae and colonies of microorganisms as persistent clogging factors. In water containing organic matter, iron, sulfur and manganese bacteria, routine oxidation with chlorine is obligatory. Chlorination can be accomplished continuously with 2 – 5 ppm of active chlorine in the water or intermittently as “shock treatment” when the build-up of slime in the system is accelerated. “Shock treatment” with 15 – 30 ppm chlorine is applied for 20 – 30 minutes. An upper threshold of 15 ppm is suggested to prevent damage to diaphragms in certain compensating emitters and hydraulic valves. A fast on-farm test indicates if the applied chlorine amount was sufficient. If the measured residual chlorine level in the distal ends of the laterals is above 0.5 – 1 ppm, sufficient chlorine had been applied. Copper sulfate is another oxidizing agent, particularly efficient in suppressing algae development in surface water reservoirs.
14.5.3. Sterilization Sterilization is a specific treatment customary in sub-surface drip irrigation systems for eliminating root intrusion into the drippers. This is done by applying the chemical Trifluralin (TreflanTM). Treflan movement in the soil is negligible and restricts sterilization to the immediate vicinity of the dripper, thus preventing damage to the root system of the grown crop. The customary application regime is 2 – 4 applications per season. The frequent applications are given in coarse textured soils. The recommended amount per application is 125 mg per dripper. Injection time is 30 – 90 minutes, depending on lateral length. Use of Treflan impregnated drippers or filters can substitute its injection into the drip system.
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15. NOMOGRAMS FOR ESTIMATION OF HEAD LOSSES IN PIPES AND ACCESSORIES
Fig. 15.1. Nomogram for calculation of head losses in water flow in pipes
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Fig. 15.2 Nomogram for calculation of head losses in LDPE pipes. Class designation relates to the working pressure (PN) in bar. 1 bar = 10 m Adapted from "Plassim" brochure
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Fig. 15.3 Nomogram for calculation of head losses in HDPE pipes. The class designation relates to the working pressure (PN) in bar. 1 bar = 10 m. Adapted from "plassim" brochure
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Fig. 15.4 Nomogram for calculation of head losses in PVC pipes. The class designation relates to the working pressure (PN) in bar. 1 bar = 10 m. Adapted from "Plastro" brochure 126
Fig. 15.5. Nomogram for calculation of local head losses in valves and other accessories and fittings
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16. BIBLIOGRAPHY American Society of Agricultural Engineers (2001). Collapsible Emitting Hose (Drip Tape) — Specifications and Performance Testing. ANSI/ASAE S553 MAR01. American Society of Agricultural Engineers (2003). Design and Installation of Micro irrigation Systems. ASEA EP405.1 FEB03 Ascough, G. W., and G. A. Kiker (2002). The Effect of Irrigation Uniformity on Irrigation Water Requirements. Agricultural Research Council - Institute for Agricultural Engineering, PO Box 2252, Dennesig 7601, South Africa School of Bio-resources Engineering and Environmental Hydrology, University of Natal, Private Bag X01, Scottsville 3209, South Africa. Attanayake, M. A. M. S. L and J. P. Padmasiri. (1994). An Appropriate Iron Removal Technology. 20th WEDC Conference: Colombo, Sri Lanka. Ayers, R. S. and D. W. Westcot. (1985). Water Quality for Agriculture. FAO Irrigation and Drainage paper 29, FAO Rome. Barber, S. A., A. Katupitiya and M. Hickey. (2002). Effects of Long-Term Subsurface Drip Irrigation on Soil Structure. Charles Stuart University, School of Agriculture, Wagga Wagga, NSW. Barth, G. (2004), Slow Flow Sand Filtration (SSF) for Water Treatment in Nurseries and Greenhouses. The Nursery Papers, South Australian Research and Development Corporation, Adelaide. Bassoi, L. H. et al. (2003). Grapevine Root Distribution in Drip and Micro-sprinkler Irrigation. Scientia Agricola, v.60, n.2, p.377-387, Apr./Jun. Benami, A. and A. Ofen. (1993). Irrigation Engineering. Agripro, Kfar Galim 30865, Israel. Boman B. and S. Shukla (2001) Materials and Installation of Delivery Pipes for Irrigation Systems University of Florida, IFAS Extension. Boman B. and S. Shukla (2004). Hydraulic Considerations for Citrus Microirrigation Systems, Circular 1425. University of Florida, IFAS Extension. Boman, B. J., P. C. Wilson, and E. A. Ontermaa (2002). Understanding Water Quality Parameters for Citrus Irrigation and Drainage Systems. Circular 1406, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Bresler, E. (1978). Analysis of Trickle Irrigation with Application to Design Problems. Irrig. Sci. 1: 3-17. Broner I. And M. Alam. (2003). Subsurface Drip Irrigation (SDI). Colorado State University Cooperative Extension. www.ext.colostate.edu. Burke, K. And Parlevliet G. (2002). Irrigation of Native Cut Flowers in Western Australia. Department of Agriculture, Western Australia. Burt, C. M., J. T. Barreras (2001). Evaluation of Retrievable Drip Tape Irrigation Systems. ITRC California Polytechnic State University, San Luis Obispo 93407. Burt, C. M. and S. W. Styles. (1999). Drip and Micro Irrigation for Trees, Vines and Row Crops ITRC, Bioresearch and Agricultural Engineering Dept., California Polytechnic State University, San Luis Obispo, 93407. Chapin R. D. (2000). A Worldwide Problem -" Drip Irrigation vs. Relief Food" An update. Chapin Living Waters Foundation. 364 N. Colorado Ave. Watertown, NY 13601 2000. Chaurette J. (2005) Centrifugal Pump Systems Fluid Design Inc. 128
Corr Tech Incorporated (2002) Engineering Guide. Dvir, Y. (1997). Flow Control Devices. Control Appliances Books. Lehavot Habashan 12125, Israel. Gerstl, Z. (1998). A Study to Compare the Release of Trifluraline into Irrigation Systems for the Purpose of Root Intrusion Prevention. Institute of Soil and Water, ARO, Volcani Center, Bet Dagan, Israel. Gleick, P. Et al. (2002). The World’s Water 2002 - 2003. Pacific Institute for Studies in Development, Environment and Security. Oakland, California. Hagin, J., M. Sneh and A. Lowengart-Aycicegi (2002). Fertigation – Fertilization through Irrigation, IPI Research Topics No. 23. International Potash Institute, P.O.Box 1609 CH-4001 Basel, Switzerland. Haman D.Z, F. Izuno and F. S. Zazueta ( 2003). Valves in Irrigation Systems, Cir 824. University of Florida, IFAS Extension. Haman, D. Z., A. G. Smajstrla and F. S. Zazueta. (1989). Screen Filters in Trickle Irrigation Systems. University of Florida, Florida Cooperative Extension Service. Haman, D. Z., A. G. Smajstrla and F. S. Zazueta. (1989). Settling Basins for Trickle Irrigation in Florida University of Florida, Florida Cooperative Extension Service. Haman, D. Z., A. G. Smajstrla and F.S. Zazueta (1994). Chemical Injection Methods for Irrigation. Florida Cooperative Extension Service. Hammami, M. et al. (2002). Approach for Predicting the Wetting Front Depth beneath a Surface Point Source: Theory and Numerical Aspects. Irrig. and Drain. 51: 347–360 (2002). Hanson, B. and D. May. (1998). Drip Irrigation Increases Tomato Yields in Salt-Affected Soil of San Joaquin Valley. UC Cooperative Extension. California Agriculture, Volume 57, No 4. Hanson, B. R., D. M. May and L.J. Schwankl. (2003). Effect of Irrigation Frequency on Subsurface Drip-Irrigated Vegetables. HortTechnology January-March 2003. Hanson, B. R., G. Fipps, E. C. Martin (2002). Drip Irrigation of Row Crops: What is the State of the Art? Kansas state University. Hartz, T .K. (1996). Drip Irrigation Improves N Efficiency. University of California, Davis. Hla, A. K. and T. F. Scherer (2003). Introduction to Micro irrigation. North Dakota State University Fargo, North Dakota 58105 Hoitink, A. J. and M. S. Krause. (1999). New Approaches to Control of Plant Pathogens in Irrigation Water. Special Circular 173-00 Ohio State University Extension Service. Intermediate Technology Consultants (ITC). (2003). Low Cost Micro irrigation Technologies for the Poor – Final Report, Oct 2003. Jayalath, J., J. Padmasiri, S. Kulasooriya, B. Jayawardena, W. Fonseka, and L. Wijesinghe. (1994). Algae Removal by Roughing Filter. 20th WEDC Conference: Colombo, Sri Lanka. Kemble, J. K. and D. C. Sanders. (2000). Basics of Vegetable Crop Irrigation. Department of Horticulture, Auburn University. Kidder, J. And E. A. Hanlon. (1998). Neutralizing Excess Bicarbonates From Irrigation Water. Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Kremmer, S. and E. Kenig. (1996). Principles of Drip Irrigation. Irrigation & Soil Field Service, Extension Service, Ministry of Agriculture, Israel (in Hebrew). 129
Kuroda M. (2005) Planning and Designing of Micro irrigation in Humid Regions. International Commission on Irrigation and Drainage (ICID). Laemmlen, F. (1998). Proper Use of Drip Tape and Fertigation will Maximize Celery Yields. 624 West Foster Road, Suite A, Santa Maria, CA 93455. Lamm, F. R. (1998). Advantages and Disadvantages of Subsurface Drip Irrigation. Northwest Research-Extension Center, Kansas State University, Colby, Kansas.
[email protected]. Luke, G. And T. Calder. (2000). Blockages in Irrigation Lines. Division of Resource Management, South Perth, Department of Agriculture, Western Australia. Maas, E. V. (1984). Salt Tolerance in Plants. In: The Handbook of Plant Science in Agriculture. B.R. Christie (ed.). CRC Press, Boca Raton, Florida. Mahbub A., P. T. Todd, F. R. Lamm and D. H. Rogers. (1992). Filtration and Maintenance Considerations for Subsurface Drip Irrigation (SDI) Systems. Kansas State University Agricultural Experiment Station and Cooperative Extension Service Manhattan, Kansas. New Mexico State University Cooperative Extension Service, College of Agriculture and Home Economics (2001) Drip Irrigation for Row Crops Circular 573. Peacock, B. (2000). Amending Soil and Water Chemistry in Drip Irrigated Table Grape Vineyards. University of California, Tulare County, Cooperative Extension. Phene, C. J. (1999). Subsurface Drip Irrigation Part I: Why and How? Irrigation Journal, April 1999. Pitts, D. (1996). Field Evaluation of Micro Irrigation System Performance. SWFREC Report No. IMM-96-OO. Southwest Florida Research and Education Center, University of Florida, Immokalee, FL. Pitts, D. J., D. Z. Haman and A. G. Smajstrla. (1990). Causes and Prevention of Emitter Plugging In Micro Irrigation Systems. Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Poffley, M. (1997). Growing Vegetables Using Black Plastic Mulch and Trickle Irrigation. Agnote 367, Horticulture Division, Darwin. Reed, D.W. ed (1996). A Growers Guide to Water, Media and Nutrition for Greenhouse Crops. Ball Publishing, Batavia, Illinois. Russo, D, J. Zaidel, A. Laufer and Z. Gerstl (2001). Numerical Analysis of Transport of Trifluralin from a Subsurface Dripper. Soil Science Society of America Journal 65:1648-1658. Rust, M. And K. McArthur. (1998). Slow Sand Filtration. Water Treatment Primer. Environmental
Information Management, Civil Engineering Dept. Virginia Tech. Salgado, E. A. and M. A. Toro. (1995). Spatial Distribution of Avocado Roots under Drip and MicroSprinkler Irrigation. Proc. World Avocado Congress III, 1995 206 – 208 Sanders, D. C. (2001) Drip or Trickle Irrigation Systems: An Outline of Components. Department of Horticultural Science, College of Agriculture & Life Sciences North Carolina State University. Sanders, D. C. (2001). Drip or Trickle Irrigation Systems: An Operations and Troubleshooting Checklist. North Carolina State University. Sands G. (2001). Soil Water Concepts. University of Minnesota. Sanjines, A. and R. Ruskin (1991). Root Intrusion Protection for Subsurface Drip Emitters. ASAE paper No. 91-2047.
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Sapir E. and M. Sne (2001) Sprinkler Irrigation. Centre for International Agricultural Development Cooperation (CINADCO), Ministry of Agriculture, Israel. Savva A. P. and K. Frenken. (2002). Planning, Development, Monitoring and Evaluation of Irrigated Agriculture with Farmer Participation, Vol. 4. FAO, Sub-regional Office for East and Southern Africa, Harare. Shock, C. (2003). Efficient Irrigation Scheduling. Malheur Experiment Station, Oregon State University 595 Onion Avenue Ontario, OR 97914. Shock, C. C., E. Feibert, and L. Saunders (2002). Irrigation Frequency, Drip Tape Flow Rate, and Onion Performance. Malheur Experiment Station, Oregon State University Ontario, OR 97914. Smajstrla, A. G., and D. S. Harrison. (1998) Tensiometers for Soil Moisture Measurement and Irrigation Scheduling. Circular 487, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Smajstrla, A. G., B. F. Castro, G. A. Clark. (1999). Energy Requirements for Drip Irrigation of Tomatoes in North Florida. Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611. http://edis.ifas.ufl.edu .edis.ifas.ufl.edu. Sne, M. (2005). Drip Irrigation. Centre for International Agricultural Development Cooperation (CINADCO), Ministry of Agriculture, Israel. Sne, M. (2006) Micro Irrigation in Arid and Semi-Arid regions – Guidelines for Planning and Design. International Commission on Irrigation and Drainage (ICID), 48 NyayaMarg, Chanakyapuri, New Delhi110 021 India. Solomon, K. S. (1992). Subsurface Drip Irrigation: Product Selection and Performance. Subsurface Drip Irrigation Theory, Practices and Applications. California State University Fresno, CATI Publication Number 92-1001 pp 3-25. Solomon, K. S. and G. Jorgensen. (1993). Subsurface Drip Irrigation, California State University Fresno, CATI. Stryker J. (2005). Backflow Preventers. Jess Stryker’s Irrigation Tutorials. Tamasi, J. (1986). Root Location of Fruit-Trees and its Agro-technical Consequences. Akademiai Kiado, Budapest, Hungary. Van Voris, P., D. A. Cataldo and R. Ruskin (1988). Protection of Buried Drip Irrigation Devices from Root Intrusion through Slow-Release Herbicides. Proceedings, 4 Intl Micro irrigation Congress, Albury-Wadonga, Australia, October 23-28, 1988. Wilcox, L. V. and C. C. Magistad. (1943). Interpretation of Analyses of Irrigation Waters and the Relative Tolerance of Crop Plants. Regional Salinity Laboratory, Bureau of Plant Industry, Soils and Agr. Engineering, Agricultural Research Administration, U. S. Department of Agriculture, Riverside, California. Wu, I-pai, H. M. Gitlin. (1979). The Manufacturer’s Coefficient of Variation Emitter Flow for Drip Irrigation. Cooperative Extension Service, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. Zoldoske, D., R. K. Striegler, G. T. Berg, G. Jorgenson, C. B. Lake, S. G. Graves, and D. M. Burnett (1998). Evaluation of Trellis System and Subsurface Drip Irrigation for Wine Grape Production: A Progress Report. CATI Publication #980401.
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Commercial Brochures and CD-ROMs Agridor Amiad Arad Ari Arkal Bermad Chapin-Watermatics Dorot
Ein Tal Eldar-Shani Galcon Haifa IDE Irrometer Mezerplas NaanDan
Netafim Plassim Odis Plastro Queen Gil Soil Moisture T-Tape Wade Rain
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17. GLOSSARY Acidification: Increasing the acidity of a solution (including soil solution) by addition of hydrogen ions (by acids or acidic agents). Air Gap: A backflow preventing technique of physical separation or maintaining air gap between two piping systems or hydraulic devices. Allowable Depletion: The percentage from Plant Available Water (PAW) that can be depleted from the active plant root zone before irreversible damage is brought about to the plant. Anti-Siphon Valve: A control valve with a built-in atmospheric vacuum breaker. Atmospheric Vacuum Breaker: A backflow prevention device that introduces air into the irrigation system when the system pressure drops to atmospheric pressure or below, to prevent back siphonage. Back Pressure: Increase of pressure downstream above the pressure at the upstream side of the connection with the supply network that would cause a reversal of the flow direction. Back Siphonage: Reversal of water flow due to pressure reduction upstream, which generates a negative pressure below the downstream pressure in the system. Backflow: Reverse flow of water in a piping system. Backflush: reverse water flow through a filter, ion exchange column, or membrane intended to remove clogging particles. Booster Pump: A pump installed in the mainline inlet for increasing the pressure in the irrigation system when the pressure in the supply system is not high enough. Bulk Density: Mass per unit volume of undisturbed soil, dried to constant weight at 105 degrees C0 expressed as g/ml. Capillarity: Moisture movement in the soil in any direction through the fine pore spaces and as films around particles. The water is drawn into small diameter virtual tubes by the adhesive forces between the liquid and the tube walls. Chemigation: Application of chemicals like fertilizers, disinfectants, oxidizers, acidifiers, soil amendment agents and pesticides through the irrigation system. Coefficient of Uniformity (Cu): A measure of the uniformity of water distribution in a defined surface area, from emitters that deliver water through the atmosphere expressed as percentage. The CU is a comparison of the average precipitation of all catchment vessels and the deviation from that average. Crop Coefficient (Kc): The decimal fraction designating the ratio between a specific crop water requirement and the reference evapo-transpiration Et0. Deep Percolation: The vertical movement of water caused by gravity downward through the soil profile, below the root zone. Design Emission Uniformity: The anticipated emission uniformity relating to the emitter’s Cv and the expected pressure variation. Design Pressure: The minimum pressure required for proper operation of an irrigation system. Diameter of Coverage: Average diameter of the area wetted by emitter spreading water through the atmosphere in wind-less conditions. Diaphragms: Flexible membranes in automatic valves, fertilizer injectors and compensating emitters that regulates the passage of water through the device.
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Double Check Valve (DCV): A device containing two independent, inline, positive seating, spring loaded check valves, two shut-off valves and ball valve test cocks. Drought: A period of dryness and insufficient soil moisture that causes extensive damage to crops and prevents their successful growth. Effective Rainfall: The amount of rain that is stored in the root zone. Electrical Conductivity: an indicator to the concentration of soluble salts in the soil solution. Elevation Gain: Pressure gained as water flows downhill from its source or a reference point. Encrustation (Soil Surface Sealing): The phenomenon in which the surface of a soil is compacted, dispersed and rearranged by the impact of raindrops. Although the surface seal is only few mm thick it dramatically reduces the infiltration rate of water. Erosion: The removal of soil particles from soil surface by weathering, running water, moving ice, wind and mass movement. Evapo-Transpiration (ET): The sum of the water amount lost through the evaporation of moisture from the soil and plant surface and the transpiration of water from the plant. Field Capacity: The percentage, per weight or per volume of the water retained in the soil after irrigation or rain when the rate of downward movement has substantially decreased, usually one to three days after irrigation or rain. Flush Flow: High initial momentary flow through a drip lateral required to flush the lateral and emitters before the working pressure is built-up. Hydraulic Conductivity: The rate at which water will move through soil in response to potential gradient. Infiltration (Intake) Rate: The dynamic rate at which irrigation or rain water applied to the soil surface will move into soil depth. The rate declines proportionally to the square root of time elapsed from the initial phase of surface hydration. Interception: The pattern and amount of precipitation that does not reach the soil surface due to blocking by the vegetation. Kilowatt-hour (KWh): A unit of electric power equivalent to the energy released by one thousand watts acting for one hour. Laminar Flow: Fluid flow that is characterized by straight flow lines in constant direction. In pipes it can be regarded as a series of liquid cylinders in the pipe, where the innermost ones are the fastest, and those near the pipe wall are the slowest. Mostly happens in low flow velocities. Leaching Requirement: the quantity of irrigation water required for removal of salts from the root zone to maintain a favorable salt balance for plant development. Maximum Allowed Depletion (MAD): The fraction of plant available water (PAW) that may be depleted from the active plant root zone without stress to the plant. Microclimate: Climate conditions in limited area that differ from the typical climate prevalent in the surrounding area. Micro-Sprayers: Inclusive designation of micro-jets, spinners, rotators, ray-jets, misters and foggers. Micro-Sprinklers: Miniature sprinklers discharging water in flow rate range of 20 – 200 l/hour. Mini-Sprinklers: Small sprinklers discharging water in flow rate range of 120 – 500 l/hour
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Mulch: 1. Organic material applied to the soil surface to protect soil from raindrop impact, improve infiltration of rain, reduce runoff, evaporation from soil surface and soil temperature fluctuations. 2. Plastic sheets used to cover the soil surface for isolating the crop from the soil surface or to facilitate efficient soil fumigation under the sheets. Neutron Probe: An instrument used to estimate soil moisture by measuring the rate of attenuation in pulsated neutron emissions that depends on soil water content. Normally Closed Valve: An automatic valve through which no water will flow unless external actuation is applied that trigger the valve to open. Most electric valves are of the normally closed type. Normally Open Valve: An automatic valve through which water will flow unless external actuation is applied to close the valve. Most hydraulic valves are of the normally open type. Orifice: Discharge hole in an emitter or lateral. Ozonation: The process of applying ozone (O3) to a liquid for disinfection purpose. Pan Evaporation: Evaporative water losses from a standardized pan used to estimate crop evapotranspiration and assist in irrigation scheduling. Percent Area Wetted: The area wetted by irrigation as a percentage of the total area in the plot. Percolation Rate: The rate at which water moves through porous media, such as the soil. Permanent Wilting Point (PWP): The amount of water in the root zone, as percentage of the soil weight or volume at or below which the plant will permanently wilt without recovery. Plant Available Water (PAW): The amount of water held within the root zone after gravitational drainage has ceased, less the amount of water that adheres tightly to soil particles and defined as the permanent wilting point. Porosity: The percentage of the soil volume that is occupied by pore spaces. Potable Water: Water from any source that has been approved for human consumption, domestic or drinkable water by the authorized health agency. Pressure Relief Valve: A valve that will be opened when its inlet pressure exceeds a preset value. Pressure Vacuum Breaker (PVB): A backflow prevention device that introduces air into the system to prevent back siphonage. employs a spring loaded seat for positive opening to atmosphere. PSI: A pressure unit in the imperial unit system, Abbreviation for pounds per square inch. Pump Curve: A graphic representation of the performance of a pump correlating the rate of flow against the total head. The efficiency of the pump can be obtainable at selected points along the curve. Reduced Pressure Backflow Preventer (RPBP): A device consisting of two positive seating check valves, and an automatically operating pressure differential relief valve located between the two check valves. It is installed between two shut-off valves. RPBP protects from backflow caused by both backpressure and back siphonage. Reducer: A fitting used to change from certain pipe diameter to a smaller one. Reference Evapo-Transpiration (Et0) of Low Crops: Represents the rate of evapo-transpiration from an extensive surface of cool-season grass cover of uniform height of 12 cm, actively growing, completely shading the ground, and not short of water. Reference Evapo-Transpiration (Etr) of Medium Height Crops: represents the rate of evapotranspiration from an extensive surface of alfalfa or similar agricultural crop of uniform height of approximately 50 cm, actively growing, completely shading the ground, and not short of water. On the average ETr is 10% - 30% greater than ETo. 135
Regulated Deficit Irrigation (RDI): Irrigation management strategy where the plant root zone is not filled with water to field capacity level or the plant water requirement is not fully met. Residual Chlorine: The total amount of chlorine remaining in water, sewage, or industrial wastes at the end of a specified contact period following chlorination; expressed in ppm units. Runoff: The flow of water over the soil surface when rainfall (or irrigation) rate exceeds the infiltration rate of the soil. Runoff can detach and remove soil particles and thus cause erosion. Runtime: Length of time available to operate an irrigation system or an individual zone for a single irrigation event. Saturated Flow: The movement of water in saturated soil (when all the pores are filled with water). Snaking: Laying of loosened laterals to allow temperature induced contraction and elongation. Soil Auger: A metallic device used for drilling into the soil and removing soil samples for analysis. Soil Probe: A soil-coring tool that allows an intact soil core to be removed from the soil profile for examination. Soil Profile: A cross-section of the whole depth of the soil at a specific site, exposed by digging a soil pit. Solenoid Valve: An automatic valve actuated by electrical signals operates under low voltage (24v AC) which may be remotely actuated and controlled via a cable or wireless from the central controller. Solvent Welding: The act of chemically fusing pipe and fittings together using solvent and cement. Spaghetti Tubing: Small tubing used in drip and trickle systems to carry water from the lateral to the emitter and from the emitter to a specific plant. Substrate: A mineral or organic material that provides anchoring medium and reservoir of water and nutrients for the plants. Sub-Irrigation: applying irrigation water below the soil surface (or the growing bed) either by raising the water table into the root zone or by use of buried perforated or emitter bearing laterals. Surface Tension: The force acting on molecules at the surface of a liquid resulting from the attraction of the liquid molecules to each other. Surge: An energy wave in pipelines caused by abrupt opening or closing of valves. Throttle: A restriction of the cross-section of water passage in valves, pipes and other water passageways. Total Dissolved Solids (TDS) - A measure (in mg/l units) of the mineral salts that will be deposited after the water had completely evaporated. Total Dynamic Head (TDH): The sum of operation head, friction head and elevation head. The total energy that a pump must incorporate in the water to guarantee optimal function of the irrigation system. Total Suspended Solids (TSS): A measure of all suspended solids in a liquid, not including the dissolved salts, expressed in mg/l. Trajectory: The angle, relating to soil surface, of the water spattered out into the air from the emitter's nozzle. Transitional (Semi Turbulent) Flow: A mix of laminar and turbulent flow, with turbulence in the center of the pipe, and laminar flow near the walls. Each of these flows behaves in different manners in terms of their frictional energy loss while flowing.
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Turbulent Flow: Flow pattern in which vortices, eddies and wakes make the flow unpredictable. The flow regime is characterized by random direction changes as well as rapid variation of pressure and velocity in space and time. Turbulent flow happens in general at high flow velocities and causes higher friction head losses than the same flow rate in laminar flow. U.P.V.C. Pipe: Unplasticized Polyvinyl Chloride pipe. Has better endurance and flexibility than ordinary PVC pipes. Water Hammer: The surging of pressure that occurs when a valve is suddenly closed or by high velocity of water flow. The surging may cause the pipes to vibrate or to burst in extreme circumstances. Water Use Efficiency (WUE): The amount of dry vegetal matter produced per unit of applied water. Expressed as g/m3 (grams of dry matter per m3 of applied water). Watering Window: The span of hours and days of the week that water is available for irrigation.
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