Drip Irrigation.pdf

Drip/Trickle Irrigation

Dr. Shahid Ali

History Primitive drip irrigation has been used since ancient times. Fan Sheng-Chih Shu written in China during the first century BCE, describes the use of buried, unglazed clay pots filled with water, sometimes referred to as Ollas, as a means of irrigation.[1][2] Modern drip irrigation began its development in Germany in 1860 when researchers began experimenting with subsurface irrigation using clay pipe to create combination irrigation and drainage systems. The research was later expanded in the 1920s to include the application of perforated pipe systems. The usage of plastic to hold and distribute water in drip irrigation was later developed in Australia by Hannis Thill. Usage of a plastic emitter in drip irrigation was developed in Israel by Polish-born Simcha Blass and his son Yeshayahu. Instead of releasing water through tiny holes easily blocked by tiny particles, water was released through larger and longer passageways by using velocity to slow water inside a plastic emitter. The first experimental system of this type was established in 1959 by Blass who partnered later (1964) withKibbutz Hatzerim to create an irrigation company called Netafim. Together they developed and patented the first practical surface drip irrigation emitter. In the United States, the first drip tape, called Dew Hose, was developed by Richard Chapin of Chapin Water matics in the early 1960s. Chapin Water matics was acquired by Jain Irrigation in 2006 and is housed under its US subsidiary Jain Irrigation Inc, USA. After its first introduction in California in the late 1960s, only 5% of irrigated land utilized this system by 1988. By 2010, 40% of irrigated land in California utilized this system. Modern drip irrigation has arguably become the world's most valued innovation in agriculture since the invention in the 1930sof the impact sprinkler, which offered the first practical alternative to surface irrigation. Drip irrigation may also use devices called micro-spray heads, which spray water in a small area, instead of dripping emitters. These are generally used on tree and vine crops with wider root zones. Subsurface drip irrigation (SDI) uses permanently or temporarily buried dripper line or drip tape located at or below the plant roots. It is becoming popular for row crop irrigation, especially in areas where water supplies are limited, or recycled water is used for irrigation. Careful study of all the relevant factors like land topography, soil, water, crop and agro-climatic conditions are needed to determine the most suitable drip irrigation system and components to be used in a specific installation.

The story of modern drip irrigation begins with a man named Simcha Blass. Born November 27, 1897 in Poland, Blass studied engineering before co-founding Mekorot, Israel's national water company, which provided water for Israel's southern Negev desert in the 1930's. Around the time that Blass was working on the first modern aqueduct in the Jordan Valley, a farmer he knew drew his attention to a large tree growing "without water". After digging around the apparently dry surface, Blass found a leaking pipe coupler was supplying water to this tree. In 1948, Blass bought up the pipes that England had used to extinguish fires during the London Blitz and shipped them home where they were used to construct a water system to supply 11 Israeli settlements and the Arab Bedouins in the Negev. After years of experimentation, a device, using water pressure and friction to control the water emitted from holes drilled at regular intervals in a plastic tube, ushered in the age of modern drip irrigation. With the advent of modern plastics in the late 1950's, Blass reopened his private engineering office with his son, Yeshayahu, and pursued the idea of commercial drip irrigation. His main goal was the creation of a product that ran the water from the pipe through an emitter with a larger and longer passageway that used friction to slow the flow to a steady drip. In the early 1960's Blass developed and patented the first practical plastic drip emitter.

Working at Kibbutz Hatzerim during this period, Blass and his son developed drip irrigation systems both in Israel and abroad. He soon found investors within the Kibbutz to purchase his technology and erect a facility for large scale manufacturing of drip tubing and emitters. Taking Blass's original "spaghetti" tubing, along with a new inline emitter developed with the aid of other engineers, they formed Netafim, the world's first drip irrigation company. In 1992, some 27 years later, DripWorks was founded on the principle that water is one of the world's most precious resources. From the beginning, Netafim has been one of our most dependable suppliers, providing the highest quality drip irrigation products available. Daniel Hillel Daniel Hillel As Dr. Daniel Hillel, recipient of the 2012 World Food Prize for his role in conceiving and implementing improved methods of food production with "micro-irrigation", said: "No one person invented drip irrigation." Still, it's clear that, for all his contributions, Simcha Blass is more than deserving of the title "Father of Modern Drip Irrigation".

Drip or trickle irrigation is a method of watering plants frequently and with a volume of water approaching the consumptive use of plants, thereby minimizing such conventional losses as deep percolation, runoff and evaporation.  Water plants by low pressure drippers or emitters put along the lateral. Water spreads laterally and vertically by silo capillary forces augmented by gravity force.

• Drip irrigation / trickle irrigation – involves dripping water onto the soil at very low rates (2-20 litres /hour),from a system of small diameter plastic pipes fitted with outlets called emitters or drippers. • Water is applied close to plants so that only part of the soil in which the roots grow is wetted. • With drip irrigation water, applications are more frequent (usually every 1-3 days). • This provides a very favourable high moisture level in the soil in which plants can flourish.

In this irrigation system: • Water is applied directly to the crop ie. entire field is not wetted. • Water is conserved • Weeds are controlled because only the places getting water can grow weeds. • There is a low pressure system. • There is a slow rate of water application somewhat matching the consumptive use. Application rate can be as low as 1 - 12 l/hr. • There is reduced evaporation, only potential transpiration is considered. • here is no need for a drainage system.

Advantages of drip Irrigation 1.High degree control of water application Field application efficiency: Drip system – 90% efficiency, Sprinkler system : 60-80 %,Surface methods :50- 60 %. The application efficiency for drip irrigation is based on the water desired in the root zone and is not based on the whole area as sprinkler and surface methods. 2. Considerable water saving 3. Advantages related to partial wetting (weed control, accessible farm, reduced fungus & insect problems, less crusting of soils).

Limitations • • • • • •

High initial investment Requires clearer water Salt accumulation at the periphery- no continuous leaching No change to the microclimate like sprinkler… Pipes are liable to mechanical damages Limited root development- localized to the wetted area.

4. To irrigate marginal soils 5. Requires lower line pressure- save energy requirement 6. Advantage of dry foliage High water potential , so that available to plants all the time.

7. Reduced salt concentration- possible to use poor quality water 8.Fertilizer application with high precision 9.Elimination of the need for Drainage.

While drip irrigation may be the most expensive method of irrigation, it is also the most advanced and efficient method in respect to effective water use.  Usually used to irrigate fruits and vegetables  System consists of perforated pipes that are placed by rows of crops or buried along their root lines and emit water directly onto the crops that need it.  As a result, evaporation is drastically reduced and 25% irrigation water is conserved in comparison to flood irrigation.  Drip irrigation also allows the grower to customize an irrigation program most beneficial to each crop.  Fertigation is possible.  Caution : Water high in salts / sediments should be filtered otherwise they may clog the emitters and create a local buildup of high salinity soil around the plants if the irrigation water contains soluble salts.

SOIL TYPE AND WATER MOVEMENT. THE APPLICATION OF WATER IS BY DRIPPERS

Suitable water

Suitable slopes Drip irrigation is adaptable to any farmable slope.  Normally the crop would be planted along contour lines and the water supply pipes (laterals) would be laid along the contour also.  This is done to minimize changes in emitter discharge as a result of land elevation changes. 

Suitable soils  Drip irrigation is suitable for most soils.

 On clay soils water must be applied slowly to avoid surface water ponding and runoff.  On sandy soils higher emitter discharge rates will be needed to ensure adequate lateral wetting of the soil.

Suitable crops Drip irrigation is most suitable for row crops (vegetables, soft fruit), tree and vine crops where one or more emitters can be provided for each plant.  Generally only high value crops are considered because of the high capital costs of installing a drip system. 

One of the main problems with drip irrigation is blockage of the emitters.  All emitters have very small waterways ranging from 0.2-2.0 mm in diameter and these can become blocked if the water is not clean.  Thus it is essential for irrigation water to be free of sediments.  If this is not so then filtration of the irrigation water will be needed.  Blockage may also occur if the water contains algae, fertilizer deposits and dissolved chemicals which precipitate such as Ca and Fe.  Filtration may remove some of the materials but the problem may be complex to solve and requires an experienced professional. 

Drip irrigation is sometimes called trickle irrigation and involves dripping water onto the soil at very low rates (2-20 litres/hour) from a system of small diameter plastic pipes fitted with outlets called emitters or drippers. Water is applied close to plants so that only part of the soil in which the roots grow is wetted (Figure 60), unlike surface and sprinkler irrigation, which involves wetting the whole soil profile. With drip irrigation water, applications are more frequent (usually every 1-3 days) than with other methods and this provides a very favourable high moisture level in the soil in which plants can flourish. Suitable crops Drip irrigation is most suitable for row crops (vegetables, soft fruit), tree and vine crops where one or more emitters can be provided for each plant. Generally only high value crops are considered because of the high capital costs of installing a drip system. Suitable slopes Drip irrigation is adaptable to any farmable slope. Normally the crop would be planted along contour lines and the water supply pipes (laterals) would be laid along the contour also. This is done to minimize changes in emitter discharge as a result of land elevation changes. Suitable soils Drip irrigation is suitable for most soils. On clay soils water must be applied slowly to avoid surface water ponding and runoff. On sandy soils higher emitter discharge rates will be needed to ensure adequate lateral wetting of the soil. Suitable irrigation water One of the main problems with drip irrigation is blockage of the emitters. All emitters have very small waterways ranging from 0.2-2.0 mm in diameter and these can become blocked if the water is not clean. Thus it is essential for irrigation water to be free of sediments. If this is not so then filtration of the irrigation water will be needed. Blockage may also occur if the water contains algae, fertilizer deposits and dissolved chemicals which precipitate such as calcium and iron. Filtration may remove some of the materials but the problem may be complex to solve and requires an experienced engineer or consultation with the equipment dealer. Drip irrigation is particularly suitable for water of poor quality (saline water). Dripping water to individual plants also means that the method can be very efficient in water use. For this reason it is most suitable when water is scarce.

Simcha Blass, an Israeli hydraulic engineer, is credited with the discovery and introduction of modern drip irrigation in the early 1930’s. Drip irrigation (also known as micro-irrigation) became more common with the introduction of plastics in the 1950’s. Plastic tubing provided an inexpensive, flexible means of delivering water to the root zone of plants and was widely used in greenhouses and for agriculture. As improvements were made to the materials and problems such as clogging were resolved drip irrigation began to gain popularity for residential and small commercial applications. The relative simplicity of drip irrigation even made it possible for homeowners and other non-professionals to install it. Benefits drip emitter Drip irrigation is arguably the most efficient method of providing water to trees, crops, gardens and landscapes. The efficiency of overhead irrigation, such as rotors, and pop-up spray heads is typically 50 percent and rarely exceeds 70 percent. The efficiency of a well-designed drip irrigation system can reach nearly 100 percent. Drip has numerous other benefits as well: • • • • • • •

It can be tailored to deliver the precise amount of water required by individual plants Evaporative losses are very low particularly when used in conjunction with mulch It is the best type of irrigation for windy conditions It uses less water since water is delivered only to the plants that need it It results in fewer weeds because the area between plants is not irrigated It reduces the incidence of foliar diseases It reduces or eliminates pollution from runoff

• • • • • • • •

It improves plant health by delivering fertilizer, and other chemicals precisely where they are needed It improves plant health by reducing fluctuations in soil moisture Its flexibility allows the system to adapt as plants grow or are added or removed It is well adapted for a wide variety of soil conditions and terrain It is often exempt from watering restrictions because it is so efficient Large areas can be watered all at once because of its low flow rate Installation and maintenance costs are typically much lower than for that of an underground sprinkler system It operates at pressures between 15 and 30 psi eliminating the need for a booster pump in low pressure systems

Disadvantages • Some contractors are reluctant to use drip irrigation despite its many advantages. The reason most commonly cited is the inability to see if it is working. Not only is there no obvious spray pattern as with overhead irrigation – drip irrigation is typically covered by a layer of mulch several inches thick. Other disadvantages include: • • • • •

Subject to damage from other landscaping activities Subject to chewing damage from rodents Subject to vandalism, particularly in areas that haven’t been mulched Can present a tripping hazard for children and pets (anchoring tubing and covering with mulch can reduce this problem) Emitters can become clogged effectively shutting off water to portions of the landscape (improvements to system filtration and self-cleaning emitters have eliminated many of these problems) • Can limit plan root growth to wetted drip area

Drip System Layout A typical drip irrigation system consists of the following components: Pump unit ,Control head, Main and submain lines, Laterals Emitters or drippers The pump unit takes water from the source and provides the right pressure for delivery into the pipe system. The control head consists of valves to control the discharge and pressure In the entire system. It may also have filters to clear the water. Common types of filter include screen filters and graded sand filters which remove fine material suspended in the water. Some control head units contain a fertilizer or nutrient tank. These slowly add a measured dose of fertilizer into the water during irrigation. This is one of the major advantages of drip irrigation over other methods. Mainlines, submains and laterals supply water from the control head into the fields. They are usually made from PVC or polyethylene hose and should be buried below ground because they easily degrade when exposed to direct solar radiation. Lateral pipes are usually 13-32 mm diameter. Emitters or drippers are devices used to control the discharge of water from the lateral to the plants. They are usually spaced more than 1 metre apart with one or more emitters used for a single plant such as a tree. For row crops more closely spaced emitters may be used to wet a strip of soil. Many different emitter designs have been produced in recent years. The basis of design is to produce an emitter which will provide a specified constant discharge which does not vary much with pressure changes, and does not block easily. Various types of emitters are shown in Figure 61 and Figure 62. Figure 63 gives an example of sublateral loops.

A drip system is usually permanent. When remaining In place during more than one season, a system is considered permanent. Thus it can easily be automated. This is very useful when labour is scarce or expensive to hire. However, automation requires specialist skills and so this approach is unsuitable if such skills are not available. Water can be applied frequently (every day if required) with drip irrigation and this provides very favourable conditions for crop growth. However, if crops are used to being watered each day they may only develop shallow roots and If the system breaks down, the crop may begin to suffer very quickly. Wetting patterns Unlike surface and sprinkler irrigation, drip irrigation only wets part of the soil root zone. This may be as, low as 30% of the volume of soil wetted by the other methods. The wetting patterns which develop from dripping water onto the soil depend on discharge and soil type. Figure 64 shows the effect of changes in discharge on two different soil types, namely sand and clay.

Wetting patterns for sand and clay soils with high and low discharge rates (CLAY) Wetting patterns for sand and clay soils with high and low discharge rates (SAND)

Wetted Area (Aw)

The wetted area depends up on: • flow rate, • soil type, • soil moisture, • vertical and horizontal permeability of the soil. Drip system is one of the latest methods and popular in areas where there is scarcity of water and salt problem. High efficiency can be achieved. ETc/dn = 0.9

Maintenance Drip irrigation systems require regular inspections and maintenance to achieve optimal performance. Drip irrigation should be inspected several times a season for: Clogged emitters – if clogging is a frequent problem install a filter at the beginning of the system. Upgrade emitters with turbulent flow emitters to reduce problems with clogging. High pressure – missing emitters may be an indicator of high pressure. A pressure regulator should be installed if missing or replaced if damaged. Emitter spacing – as plants grow emitters must be moved to accommodate expansion of the root zone. Emitters may be moved inadvertently during weeding and other horticultural practices. Missing emitters – any missing emitters should be replaced immediately to maintain the efficiency of the system. Missing emitters may be an indicator of high pressure – check to make certain a pressure regulator is installed and functioning. Damaged tubing – tubing can be cut or pinched as a result of horticultural practices or plant overgrowth. Damaged tubing may need to be replaced, straightened or moved.

• The Major Components of a Drip Irrigation System include: • a) Head unit which contains filters to remove debris that may block emitters; fertilizer tank; water meter; and pressure regulator. • b) Mainline, Laterals, and Emitters which can be easily blocked. • The design of drip system is similar to that of the sprinkler system except that the spacing of emitters is much less than that of sprinklers and that water must be filtered and treated to prevent blockage of emitters. • Another major difference is that not all areas are irrigated. • In design, the water use rate or the area irrigated may be decreased to account for this reduced area.

A typical drip irrigation system of the following components:  Pump unit  Control head  Main line  Laterals  Emitters or drippers. • Main line, sub main and lateral. The mainline has a pump to pressurize the system and possibly a chemical injector to conveniently apply nutrients through the distribution system. • Primary filter- for coarser materials • Primary pressure gauge • Discharge control valves • Flow meters • Secondary filter- for finer materials • Solenoid valve- for pressure automation. An emitter (dripper) is a device which applies water to the soil from the distribution system. Types of emitters: Line source Point source emitters OR They can be can be laminar flow type, turbulent flow type or pressure compensating type.

Emitter flow regime • A turbulent flow vortex emitter has increased pressure loss through the orifice compared to that operating in a laminar flow regime. • A pressure compensating emitter, aims at maintaining a constant distribution system. • The flexible membrane or diaphragm responds to pressure changes and keeps discharge constant with in the design specifications. • A trickle line may be designed to operate under a pressure as low as 0.4 atm and as high as 1 to 1.75 atm. • A pressure drop of 0.5 to 1.0 atm. may be anticipated in the head of the drip system, including the filter. • There is a further drop of pressure in the lateral • In the emitters the pressure is reduced to nil so that the water leaves the emitter at atmospheric pressure as a drip, at a flow rate of 2 to 10 litters per hour. Emitter discharge and its variation Average discharge or nominal discharge @ 1atm. and 20oc , this varies w.r.t pressure.

Manufacturer’s variation- coefficient of variation (cvf) and it varies between 0.02 and 0.5 of the nominal discharge. All pressure at the inlet should be dissipated to a level nearly equal to the atmospheric pressure, at the outlet. This is so by using:Long narrow flexible PVC or PE tubes (Micro tubes/capillary tubes) • Nozzles or orifices of small size, varying between 0.4 to 0.6mm. • Smaller perforations on the trickler line. • Spiral water paths (Coiled Microtubes or Screw threads)

Pump unit takes water from the source and provides the right pressure for delivery into the pipe system.  The control head consists of valves to control the discharge and pressure in the entire system.  It may also have filters to clear the water.  Common types of filter include screen filters and graded sand filters which remove fine material suspended in the water.  Some control head units contain a fertilizer or nutrient tank.  These slowly add a measured dose of fertilizer into the water during irrigation.  This is one of the major advantages of drip irrigation over other methods. 

Supply water from the control head into the fields.  They are usually made from PVC or polyethylene hose and should be buried below ground because they easily degrade when exposed to direct solar radiation.  Lateral pipes are usually 13-32 mm diameter.  Emitters or drippers are devices used to control the discharge of water from the lateral to the plants.  They are usually spaced more than 1 metre apart with one or more emitters used for a single plant such as a tree.  For row crops more closely spaced emitters may be used to wet a strip of soil.  Many different emitter designs have been produced inrecent years.  The basis of design is to produce an emitter which willprovide a specified constant discharge which does not vary much with pressure changes, and does not block easily. 

The water savings that can be made using drip irrigation are the reductions in deep percolation, in surface runoff and in evaporation from the soil.  These savings, it must be remembered, depend as much on the user of the equipment as on the equipment itself.  Drip irrigation is not a substitute for other proven methods of irrigation.  It is just another way of applying water.  It is best suited to areas where water quality is marginal, land is steeply sloping or undulating and of poor quality, where water or labour are expensive, or where high value crops require frequent water applications. 

Internally built in

Types of emitters w.r.t flow regimes

1.Orifice drippers: -The low discharge rate and pressure reduction are achieved by relatively small hole of 0.4 to 0.6 mm in diameter -The orifice dripper is relatively cheap but has the drawback that the small hole easily is clogged up by dirt . - orifice should be situated at the entrance –reduce clogging. -Orifice discharge equation:

Q  KA 2 gh

2. Long straight flow path tricklers - Microtubes • In this type of dripper polyethylene microtubes are used. • Resistance to flow is proportional to tube length.

•

• •

Suitable for undulating topo., where pressure variation is inevitable condition along the flow direction. Susceptible to rodents Suction problem – then clogging.

.

3 Long spiral flow path trickles

A micro tube wound in the form of a coil Can be - Pre - coiled micro tubes - Labyrinth emitters (internal spiral emitters) – whose principle is similar to that of long path emitters, they are called inline emitters.

•

In calculating the discharge of a micro tube dripper it is supposed that the pressure in the tube is reduced to nil and the flow is laminar.

The spiral flow in labyrinth tricklers produces centrifugal forces and a greater resistance to the flow.

•

In long path trickler:

Temperature has much influence on the discharge of long flow path drippers. As far as the flow is laminar, the discharge is inversely proportional to the viscosity of the water.

• The drawback of micro tube drippers is that the tolerable pressure variation in trickle line is lower than for orifice drippers – larger diameter pipes are required , • efficiency falls rapidly for small variation in pressure. Remedy: select appropriate tube length.

The diminishing increase of the discharge is the consequence of the fact that the flow becomes more and more turbulent under higher discharges, resulting in a decreasing influence of the viscosity of the fluid

Single-exit orifice type emitter

Multi-exit long path emitter

Single-exit long path emitter

Orifice –vortex type emitter

4. Vortex drippers The vortex dripper is an improved orifice dripper. Attempts have been made to increase the orifice diameter of orifice drippers, in order to reduce the tendency of clogging, by increasing the flow resistance by a spiral construction of the inlet. The water enters tangentially to the circumference of a circular chamber and causes a fluid to whirl around - centrifugal forces comes into operation and these forces produce greater resistance to the flow. The advantage of a vortex dripper is that its diameter (for same q and H) can be approximately 1.7 times larger than that for a simple orifice type. However, low discharge as 2.4 lt/hr at 10m of water pressure is difficult to obtain.

Other types of drippers • Twin-wall trickler (bi-wall trickle lines). • Large calibrated orifices with sleeve system.

Pipelines • Most of the plastic pipelines used in irrigation are composed of the following four kinds of materials.

-polyvinyl chloride (PVC) -polypropylene (PP)

-polyethylene, low density (PEb) and high density ( PEh)

-Acrylonitrile - Butadiene - Styrene (ABS)

• • •

PVC, PEb and PEh are by far the most widely used in trickle irrigation. PVC is more economical in large sizeshigher hydrostatic design stress. PE’s for lesser size and where flexibility is the issue

Criteria for the selection of plastic pipelines. 1. Pressure (class) rating (PR ) -This is the estimated maximum water pressure that pipe can withstand continuously with a high degree of certainty that failure of the pipe will not occur. 2. Maximum operating pressure (MOP) - which is the maximum

allowable operating pressure taking into account a safety factor (higher than the one entering in the determination of PR).

• Utmost PR could be equal to MOP. However this doesn’t provide allowance for water-hammer pressures. • PR & MOP = f ( Dia. , L , t) of pipe • SDR (Standard Dimension Ratio)- is the ratio of the average pipe diameter to minimum wall thickness. SDR = D / t For PVC and ABS pipes , SDR = Dout / tmin. For PE pipes , SDR = Din / t.

Relation between SDR, hydrostatic design stress ,S and pressure rating, PR - (ISO) • For PVC and ABS pipes: 2S = SDR - 1 or 2S = DO - 1 PR

PR

t

• For PE pipes 2S = SDR + 1 or 2S = DI + 1 PR

PR

t

Where, S = the hydrostatic design stress or the maximum tensile stress in the wall of the pipe due to internal hydrostatic water pressure that can be applied continuously with a high degree of certainty that failure of the pipe will not occur. DO and DI = outside and inside diameters respectively. t = wall thickness. Note: MOP < 0.72 PR

• For trickle irrigation, calculation of the peak demand is very complicated since only a part of the root system is irrigated. • When an unshaded surface is wetted by surface or sprinkler irrigation, a portion of the potential benefit of the water applied is lost through evaporation from the soil or transpiration from weeds. • Therefore, the figures of crop water requirements determined by conventional methods include the non-beneficial evaporation or transpiration. Consequently a reduction factor, kr, should be applied to the conventional ETcrop calculations.

1.Keller and karmeli ( 1974 ) suggest

Kr 

Whichever is the smallest

GC or 1 0.85

GC%

Kr

Kr

Kr

Keller and Karmeli

Freeman and Garoli

Decroix

0.12 0.24 0.35 0.47 0.59 0.70 0.82 0.94 1 1

0.10 0.20 0.30 0.40 0.75 0.80 0.85 0.90 0.95 1

0.20 0.30 0.40 0.50 0.60 0.70 * 0.80 * 0.90 * 1* 1*

2. Freeman and Garzoli suggest Kr = GC + 1/2 (1 - GC) 3. Decroix, proposes

Kr = (0.10+GC) or 1, which ever is the smallest GC = is the fraction of the total surface area actually covered by the foliage of the plants when viewed from directly above.

10 20 30 40 50 60 70 80 90 100

The net irrigation requirement

The overall application efficiency of trickle irrigation

IRn = ETcrop* kr +Lr – R R = Water received by the plant from sources other than Irrigation • R includes Rainfall ,stored soil water , GW contribution, seepage contribution etc. The gross irrigation requirement

Ea = ks.*Eu Where: ks = coefficient (<1) which expressed the water storage efficiency of the soil. deep percolation , other losses ks =

Average water stored in the root zone average water applied

IRg = IRn/Ea Ea = the irrigation efficiency. • Even if ideally all emitters have the same discharge at a certain pressure, the distribution will be irregular due to unavoidable pressure variation in laterals and due to emitters manufacturing errors.

Eu = coefficient (<1), which reflects the uniformity of application (distribution), discharge efficiency. It estimates the percentage of average depth of application required by a system to irrigate adequately the least watered plants.

EU  100

q lq 

q

Average of the lowest 25% field data of emitter discharge

Average of the lowest 100% field data

The variation in discharge rates between the different emitters is a function of the unavoidable pressure variations in the laterals, discharge characteristics or emitters and manufacturing errors .

Discharge Efficiencies in Drip Laterals (Baars, 1976) Pressure Orifice Trickler Long spiral path Long straight path variation trickler trickler H1/Hn

Emission uniformity

CV  f  EU  1001.0  1.27  n 

q  min imum  q  average q

 min imum EU  1001.0  1.27CV f (total)  q  average

1.05 1.10 1.15 1.20 1.25 1.30

Discharge variation Q1/Qn

Water losses %

Discharge Efficiency %

Q1/Qn

Water losses

Eu %

Q1 Qn

Water losses

Eu %

1.025 1.050 1.075 1.095 1.120 1.140

0.8 1.7 2.5 3.2 4.0 4.7

99.2 98.3 97.5 96.8 96.0 95.3

1.037 1.074 1.111 1.147 1.187 1.217

1.2 2.5 3.7 4.9 6.1 7.2

98.8 97.5 96.3 95.1 93.9 92.8

1.05 1.10 1.15 1.20 1.25 1.30

1.7 3.3 5.0 6.7 8.3 10.0

98.3 96.7 95.0 93.3 91.7 90.0

CVf = coefficient of manufacturing variation of the emitter, obtained from the manufacturer or by equation (CVf = /qav.), CVf(total) = system coefficient of manufacturing variation, N= minimum number of emitters per plant, qminimum = minimum emission rate computed from the minimum pressure in the system, based on the nominal flow rate-vs pressure curve, qaverage = average or design emission rate.

H1 = Hn = Q1 = Qn =

pressure at the first trickler pressure at the end trickler discharge of the first trickler discharge of the end trickler

Depth of application

Irrigation Interval

The maximum net amount of water that can be applied per irrigation

:

D  ( FC  PWP ) * Drz * MAD *

p ( FC  PWP ) * Drz * MAD * 100 T ET * Kr  R  Lr crop( peak)

P 100

P= the volume of soil wetted as a % of the total volume

Soil texture

Crop

Drz(m)

Tomatoes Vegetables Citrus Deciduous fruits Grapes

1-0 - 1-2 0-3 - 0-6 1-0 - 1-2 1-0 - 2-0

Sandy

1-0 - 3-0

clay loam

Sandy loam Loam

Silty clay

As a general rule the allowable moisture deficit is often taken as 0.3 (30%) for drought-sensitive crops and up to 0.6 (60%) for non-sensitive crops.

Clay

Available Moisture percentage by weight FC WP Available 9 4 5 (6-12) (2-6) (4-6) 14 6 8 (10-18) (4-8) (6-10) 22 10 12 (18-20) 98-12) (10-14) 27 13 14 (25-31) (11-15) (12-16) 31 15 16 (27-35) (13-17) (17-18) 35 17 18 (31-39) (15-19) (16-20)

Holding capacity by volume mm/m 85 (70-100) 120 (90-150) 170 (140-190) 190 (170-220) 210 (180-230) 230 (200-250)

Water Use for Trickle Irrigation System

Emitters 

Consist of fixed type and variable size types.  Karmeli and Keller (1975) suggested the The fixed size emitters do not have a  following water use rate for trickle irrigation design mechanism to compensate for the friction  ETt = ET x P/85 induced pressure drop along the lateral while  the variable size types have it.  Where: ETt is average evapotranspiration rate for crops  Emitter discharge may be described by: under  q=Khx trickle irrigation;  Where: q is the emitter discharge; K is  P is the percentage of the total area shaded by crops; constant for each emitter ; h is pressure head  ET is the conventional evapotranspiration rate for the crop. at which the emitter operates and x is the E.g. exponent characterized by the flow regime. If a mature orchard shades 70% of the area and the conventional ET is 7 mm/day, the trickle irrigation design rate is:  7/1 x 70/85 = 5.8 mm/day  OR use potential transpiration, Tp = 0.7 Epan where Epan is the evaporation from the United States Class A pan.

Water Distribution from Emitters 

Emitter discharge variability is greater than that of sprinkler nozzles because of smaller openings(lower flow) and lower design pressures.  Eu = 1 - (0.8 Cv/ n 0.5 )  Where Eu is emitter uniformity; Cv is manufacturer's coefficient of variation(s/x ); n is the number of emitters per plant.  Application efficiency for trickle irrigation is defined as:  Eea = Eu x Ea x 100  Where Eea is the trickle irrigation efficiency; Ea is the application efficiency as defined earlier.

Pressure Head at Manifold Inlet   

Like Sprinklers, the pressure head at inlet to the manifold: = Average Operating Head = 8.9 m + 75% of Lateral and Manifold head Loss = 0.75 (0.51 + 0.68)  + Riser Height = Zero for Trickle since no risers exist.  + Elevation difference = Zero , since the field is Level  = 9.79 m solution  Total Head for Pump  = Manifold Pressure = 9.79 m  + Pressure loss at Sub-main = 6.59 m  + Pressure loss at Main = 2.90 m  + Suction Lift = 20 m  + Net Positive Suction head for pump = 4 m (assumed)  = 43.28 m  i.e. The Pump must deliver 3.23 L/s at a head of about 43 m.

Micro-Spray Irrigation micro-spray 1Micro-spray is a cross between surface spray irrigation and drip irrigation. It has some of the advantages and some of the disadvantages of each type of irrigation. Like drip irrigation, microspray is considered a type of low-pressure irrigation typically operating with pressures between 15 and 30 psi. It is generally considered low volume with application rates of 5 to 70 gallons per hour (gph) (18.9 Lph to 264 Lph). Micro-spray typically creates a larger wetted area then drip irrigation making it well suited for irrigating ground covers, large flowerbeds and sandy soil. Micro-spray is delivered through micro tubing to a series of nozzles attached to risers. These risers may be fixed or designed to pop-up. In either case, it is easy to see that they are functioning, eliminating the most commonly voiced complaint about drip irrigation. It provides many of the same benefits as drip irrigation with a few exceptions: It is less likely to be exempt from watering restrictions because it puts out a higher volume of water than drip irrigation It is subject to evaporative losses and spray pattern disruption in windy conditions Higher flow rates make it more susceptible to overwatering and runoff Larger wetted areas may result in more weeds

Maintenance Micro-spray maintenance is similar to that of drip irrigation although it uses nozzles instead of emitters to deliver water. Nozzles are subject to clogging and disruption of flow pattern. Nozzles can be blown off due to high pressure; tampering with flow adjustments can result in flows that are too high or too low for the landscaped area being irrigated

Microsprinklers

Bubblers

Micro irrigation: Appropriateness

Micro irrigation: Appropriateness: Methods based on imported components • Manufactured drip emitters and microsprayer assemblies are carefully supervised and maintained. • Ancillary equipment such as screen and media filters, metering valves, pressure regulators and fertilizer injectors are used in various combinations.

Methods based on imported materials but local fabrication • Moulded plastic pipes or extruded plastic tubing are perforated manually and laid over the ground to simulate drip irrigation. • Vertical sections of plastic pipes (or even discarded plastic containers such as bottles) are embedded in the ground. • Thin-walled plastic vessels are filled with sand or gravel to provide mechanical resistance to crushing. • Slit plastic sleeves cover the perforated sections of the tubes to prevent root penetration into the outlet holes. • Sand filters prevent suspended particles or algae from clogging the outlets. • Auxiliary containers are used to dissolve and inject fertilizer into the irrigation water. • Vertical standpipes are used to deliver water from an underground pipe to small basins.

• Low-fired porous ceramic pots are placed on the surface or embedded in the soil within the root zone. When filled with water and dissolved fertilizers, the permeable clay receptacles ooze water and nutrients into the soil. • Sectioned ceramic pipes constitute line sources that feed elongated beds. • The technology must offer the farmer sufficient financial return or a reduction in labour demand, to justify the investment • Farmers need to grow high value crops for an assured market in order to cover costs • Increasing national or regional water shortage is an important factor motivating governments to promote the use of modern irrigation technologies

Clay pot method

• Governments must enact policies promoting the technologies for the smallholder, making it attractive to manufacturers and dealers to develop and promote them • Suitable systems must be relatively cheap and straightforward to operate and maintain • Farmers require effective technical support in the initial years – failure = ruin

What is Micro Irrigation? Slow & regular application of water directly to the root zone of plants through a network of economically designed plastic pipes and low discharge emitters. What are IDEal Micro Irrigation Systems (IMS)? IDEal Micro Irrigation Systems encompass low-cost drip and sprinklers. IDEal systems are assembled and packaged for small plots along with user-friendly instruction manuals that enable small holders to cultivate commercial crops. In other words, micro irrigation can maximize crop productivity and protect the environment through conserving soil, water and fertilizer resources, while also increasing farmer income. However, a majority of smallholders in developing countries are deprived of this technology due to its high capital cost and non-adaptability to small land holdings. Until recently, it has been too expensive to be affordable for poor families and too large for tiny plots of land. International Development Enterprises (IDE), a non-profit development organization, has overcome this problem by developing a range of small, easy-to-use, and affordable micro irrigation kits. IDEal Micro Irrigation Systems allow the production of high value crops with less time and money than traditional ways of c u l t i v a t i n g a n d i r r i g a t i n g commercial crops. An e x amp l e o f o n e o f t h e s e technologies is the low-cost IDEal Drip System, consisting of a network of plastic pipes with emitters. The emitters deliver water directly to the root zone in quantities that approach the consumptive use of the plants. Most of the components in a typical low-cost micro irrigation system are manufactured from polyvinyl chloride and various types of polyethylene and polypropylene. The manufacturing technology is based on a simple extrusion or injection molding process. Because of this, manufacturers of plastic pipes can easily adapt the technology to the needs of the smallholders and enable them to cultivate high-value cash crops with small amounts of water to increase their income. With the use of the technology, smallholders are able to increase their income up to two to three times what they make from traditional crops. With available water, farmers can also increase their productive area when using IDEal Micro Irrigation Systems.

Advantages of IDEal Micro Irrigation Systems (IMS) Some of the major advantages of IMS are given below:

4. Mainline: Pipe made of poly vinyl chloride (PVC) or 1. Water Source: The IDEal Drip System is a low-pressure polyethylene (PE) to convey water from the source to the system that uses gravity to increase water pressure. The water submain line. PE pipe material is normally made from highsource can be an overhead tank placed at a minimum of one density polyethylene (HDPE), low-density polyethylene meter above ground level for smaller systems up to 400 m2 area. (LDPE) and linear low-density polyethylene (LLDPE). The size Forlarger systems, the height of the tank should be increased. If of pipe depends on the flow rate of water in the system. the height of the tank is not increased, the system can be connected to a pump that lifts 5. Sub-main: Made of PVC / HDPE / LDPE / LLDPE pipe water from sources such as a well, farm pond, storage tank, or a to supply water to the lateral pipes. Lateral pipes are connected to the sub-main pipe at regular intervals. The size stream / canal. A manually operated of pipe depends on the flow rate of water in the system. pressure pump also can be used to lift water from a shallow water table (up to 7 meters) and used for the system. 6. Lateral: Pipes made of LLDPE or LDPE placed along the 2. Control Valve: A valve made of plastic or metal to regulate rows of the crop on which emitters are connected to provide required pressure and flow of water into the system. There are water to the plants directly. The lateral pipe size is from 12 valves of various sizes depending on the flow rate of water in mm to 16 mm in most IDEal Drip Systems. the system. 3. Filter: The filter ensures that clean water enters the system. There are different types of filters - screen, media and disc. Different sizes of filters are available depending on the flow rate of water in the system.

7. Emitters: A device through which water is emitted at the root zone of the plant with required discharge. Different types of emitters used in IDEal Drip Irrigation Systems are described below: i) Micro-tube: Straight or curled LLDPE tube with an inner diameter ranging from 1 to 1.2 mm. The discharge from the micro-tube is directly proportional to the operating pressure and inversely proportional to its length. The operating pressure that is required can be as low as 1-5 meters.

ii) Straight Connector: The straight connector is also called a joiner and is required to connect pipes. It can be either the equal joiner or reducing joiner including 12mm x 12mm, 12mm x 16mm, 25mm x 32mm, 32mm x 40 mm, and iii) Take-Off Tee: It is used to connect the lateral pipes to the sub-main pipe in larger systems. It is fixed in the wall of sub-main pipe with the help of a rubber washer called a gromate. It is available for different sizes of lateral pipes including 12mm and 16mm.

ii) Drip Tape / Built-in Dripper: It has built-in drippers / iv) Wooden Guide: It is used to protect the bottom of the suboutlets on the lateral line which give a continuous wetting strip. main pipe while the metal punch is used to punch a hole in the It is mainly used for row crops. The operating pressure required sub-main pipe from the top. is from 1-5 meters. 8. Fittings & Accessories: Various fittings required in IDS v) Metal Punch: It is used along with the wooden guide to are described below. punch a hole on the top of the sub-main pipe in order to connec i) Tee Connector: Tee Connector: Tee connectors of various the take-off tee to the sub-main pipe. sizes are required in IDEal Drip Systems to connect a branch to the main pipe, themain pipe to sub-main pipes, the lateral pipes to sub-main pipes, etc. The tee connectors can be either the equal tee or reducing tee type including 12mm x 12mm, 16mm x 12mm, 16mm x 16mm, 25mm x 12mm, and 32mm x 12 mm.

Sprinkler Head:A device through which water is emitted near the plant. There are three types of sprinklers as given below: i) Micro-Sprinkler: It has a small rotating device to spray water as light precipitation. It covers an area with radius of 3-4 meters. Operating pressure required is 5-10 meters. ii) Mini Sprinkler: It has a small rotating device to spray water as light precipitation. It covers an area with a radius of 6-8 meters. The operating pressure required is 5-15 meters. iii) Impact Sprinkler: It is made of metal or plastic and has a spring which makes the hammer move, rotating the sprinkler. It covers an area with a radius of 10-12 meters and operating pressure required is 10-20 meters.

Drip Kit

Micro Sprinkler

Mini Sprinkler

Design Inputs: IDEal Drip System kits are designed to provide high irrigation efficiency and uniform distribution of water and nutrients for high value crops as compared to conventional flood irrigation systems. If a larger system is required by the farmer, it can be designed within the allowable discharge variation limit by using the following procedure. The inputs required to make an effective customized drip micro irrigation system are as follows: 1. Layout of the area 2. Details of the water source and soil type 3. Agronomic details (plant spacing, crop period, season, canopy, etc.) 4. Climatic data (rainfall, temperature, evapo-transpiration, etc.) By using this information, a complete drip micro irrigation system can be designed which will give the following outputs.

Design Outputs: By using this information, a complete drip micro irrigation system can be designed which will give the following outputs. 1. Detail layout of the system in the field 2. Emitter selection and placement 3. Size and length of mainline, sub-main and lateral pipes 4. Pumping and filtration requirement 5. Operating schedule for irrigation. 6. Material and cost estimate Water Requirement 6.3.5 Operating Time / Irrigation Schedule The water requirement of plants depends on many factors viz. temperature, humidity, soil type, wind velocity, growth stage, shade / sun, etc. Plants absorb soil moisture and transpire it to the atmosphere during the process of photosynthesis. Some amount of water is retained in the plant tissue and the rest of the soil moisture gets evaporated to the atmosphere. Drip irrigation involves frequent application of water, even on a daily basis. Therefore, water requirement of the plant per day is equivalent to the rate of potential evapo-transpiration per day. Evapo-transpiration is the quantity of water transpired by the plants plus the quantity of water retained in the plant tissue and water evaporated from the soil surface. The reference values for evapo-transpiration are normally available for a particular area at the nearest meteorological observatory. Water requirement can be calculated as:

WR (Liters per day) = ET x Kc x Cp x Area, where ET is evapo-transpiration (mm per day) Kc is crop factor Cp is canopy factor Area in sq. meter

Example: Calculate peak water requirement for grapes planted at the spacing of 2 m by 2m. Assume peak ET for the area as 6 mm per day, crop factor for grape 0.8 and canopy factor 0.8. Peak water requirement per day = 6 x 0.8 x 0.8 x 2 x 2 = 15.4 liters per day per plant It is called peak water requirement because it is calculated on the basis of the highest rate of evapo-transpiration which normally occurs in the high temperatures and windy conditions of summer. However, daily water requirements will depend on the daily rate of evapo-transpiration which is less during winter and higher in summer. The drip system has constant discharge at the given pressure. Therefore, operating time can be varied to provide the required amount of water depending on the season. Operating (irrigation) time is the duration of irrigation system operation that provides the required amount of water for the plants. It can be calculated as follows: Water requirement (liters per day) Irrigation time (hrs / day) = ————————————————————Application rate (liters per hour)

Example 1 Calculate irrigation time for a papaya tree with daily water requirement of 10 liters per day per plant and provided the microtube system with a discharge rate of 4 liters per hour. 10 Irrigation time (hrs / day) = —— = 2.5 hrs / day 4

Example 2 Calculate the irrigation time required for a 100 sq. meter vegetable plot with a daily water requirement of 400 liters and a microtube system discharge rate of 200 liters per hour. 400 Irrigation time (hrs / day) = —— = 2 hrs / day

Selection of Emitter The emitter is the most important part of a drip system because it delivers water at the desired rate to the plant and maintains water application uniformity over the entire irrigated area. An emitter should match particular field conditions including type of crop, spacing of the plants, terrain, water requirement, water quality, operating time, pressure head, etc. Some of the criteria that can be applied to the selection of dripper are given below: 1. Reliability against clogging and malfunctioning 2. Emission uniformity 3. Simple to install and maintain 4. Pressure compensation in case of undulated terrain 5. Percentage area wetted 6. Flow rate 7. Operating pressure 8. Cost

Design of Lateral In most of the drip systems LLDPE laterals of 12 mm to 16 mm size are used. An important point to consider while designing the lateral pipe is the slope of the field. If the average slope of the field is less than 3% in the direction of the lateral, laterals can lie along the slope. However, if the slope of the field is more than 3%, laterals should be used along the contours. Additionally, friction loss along the laterals must stay within the allowable limit. This limits the length laterals can be along each side of the sub-main line. The desirable limit for emitter flow variation is less than 10%, but depending on the crop, variation of 10 to 20% is acceptable. For 10% variation in discharge, approximately 20% variation in the available head is acceptable. Taking into consideration all of these limitations, the maximum allowable length of laterals can be calculated from flow equations like the Hazen-Williams equation (using C 150): To cover the range of emitter discharge and spacing, a parameter called Specific Discharge Rate (SDR) is used. It is actually flow per unit length of the lateral. It can be calculated as given below.

The following tables give allowable lengths for 8 mm, 12 mm, 14 mm & 16 mm pipe at different pressure head and lateral flow rates.

Note : The above figures are for flat land (zero slope.) Pipe length adjustments must be made if the slope is above zero. Use lateral pipes along the contour line and shorter sub-main pipe against the slope and longer sub-main down the slope so that discharge variation is within desired uniformity levels.

Design of the sub-main The sub-main pipe is designed similarly to the lateral lines because it is also a perforated pipe whose discharge reduces along the length of the pipe. Depending on the flow rate, various sizes of PVC / HDPE / LLDPE pipes are used as sub-main pipes in micro irrigation system. For IDEal Drip System klits, 16 mm, 32 mm and 48 mm Lay Flat LLDPE pipe is used for the sub-main pipe. The calculation of the allowable length at different pressure heads and flow rates for 32 mm, 48 mm, 63 mm and 75 mm is given below.

Design of Main Line Design of the main line involves determining the diameter of the pipe and class / thickness. It depends upon flow rate, operating pressure and topography. As per the irrigation scheduling of the sub-main units, the main line flow can be determined by selecting the sub-mains that will operate concurrently. The main line size is selected so that allowable pressure variations due to frictional losses are within the limit for the economic pipe sizing. Frictional head loss can be calculated using the Hazen-Williams equation as given below.

Selection of Filter The filtration requirement depends on the size of the flow path in the emitter, quality of water and flow in the mainline. IMS Kits use screen filters because water is stored in a storage tank. For large systems, depending on water quality, different filters or combination of filters can be used. For large flow requirements filters can be connected in parallel using manifolds so that pressure loss across the filters is within limits. Four types of filters are mainly available in different sizes (filtration area) as described below. 1. Screen (Mesh) Filter: It is made of plastic or metal and different sizes are available for different flow rates from 1 m /hr to 40 m /hr. It is used for normal water with light inorganic impurities. It is also called a surface filter. 2. Sand (Media) Filter: It is made of M.S. metal and available in different sizes similar to the screen filter. It is used for water with suspended particles and organic impurities like algae. Either sand or gravel can be used as the media for filtration. It is also called a depth filter. and is used in series with the screen filter. 3. Disc Filter: It is made of plastic and has round discs with micro water paths, staked together in a cylinder so that impurities can not pass through the discs. It combines surface and depth filters. 4. Hydro-cyclone: It is made of M.S. metal and has a conical shaped cylinder to give centrifugal action to the flow of water so that heavy impurities settle. It is used in conjunction with the screen filter to filter sandy water along.

Selection of Pump / Total Head Requirement The head (pressure) required at the inlet of the mainline or filter is calculated as follows: Head (m) = Operating pressure (m) + Mainline friction loss (m) + fittings loss (m) + Filter loss (m) + (-) Elevation difference (m).

For a centrifugal pump the total head requirement is calculated as follows: Total Head (m) = Suction head (m) + Delivery head (m) + Operating pressure (m) + Mainline friction loss (m) + fittings loss (m) + Filter loss (m) + (-)Elevation difference (m).

The horsepower requirement is calculated as follows: Flow (lps) x Total Head (m) Horsepower (HP) = ————————————————————————75 x Motor efficiency x Pump efficiency Efficiency of the motor and pump differ for different makes and models. Approximate motor efficiency can be assumed at 80% and pump efficiency at 75% for a mono-block pump. However, in order to procure a pump from the market, the required flow and total head should be mentioned to the supplier / manufacturer so that he can select a suitable model from the same or lower horsepower category.

The following general checks can be carried out periodically depending on the local condition and water quality: 1. Clogging of emitters / micro sprinklers and wetting pattern 2. Placement of emitters / micro-tubes / micro sprinklers 3. Leakages in pipes, valves, filter, fittings, etc. 4. Flushing & cleaning of filter by opening and cleaning the screen 5. Flushing of sub-main & laterals by releasing the end caps

Crop

Yield Increase (%)

Water saving (%)

Bananas

52

45

Grapes

23

48

Sweet lime

50

61

Pomegranate

98

45

Papaya

75

68

Tomato

50

39

Watermelon

88

36

Okra

16

40

2

60

Chillies

44

62

Sweet Potato

39

60

Beetroot

7

79

Radish

2

77

Sugar cane

33

56

Cotton

26

53

Cabbage

Micro irrigation

• Excellent efficiency (>0.9) • “little and often” - plants have ideal water all the time • As little as 30% of the root zone is wetted

• • • • • •

Not sensitive to slope Good for mineralised water Good for injected fertiliser But Very expensive Needs well filtered water Can be complex to operate ands maintain

SUB-SURFACE IRRIGATION 

Applied in places where natural soil and topographic condition favour water application to the soil under the surface, a practice called sub-surface irrigation. These conditions include:  a) Impervious layer at 15 cm depth or more  b) Pervious soil underlying the restricting layer.  c) Uniform topographic condition  d) Moderate slopes. 

The operation of the system involves a huge reservoir of water and level is controlled by inflow and outflow.  The inflow is water application and rainfall while the outflow is evapotranspiration and deep percolation.  It does not disturb normal farm operations. Excess water can be removed by pumping.

Glossary of Terms Backflow prevention device – a device that prevents contaminated water from being sucked back into the water source should a reverse flow situation occur. Bubbler – a water emission device that tends to bubble water directly onto the ground or that throws water a short distance. Control valve – a device used to control the flow of water. Control valves turn water to the individual zones on and off. Drip irrigation – a method of irrigation using the slow application of water under low pressure through tube openings or attached devices just above, at or below the soil surface. Drip line – the circle that could be made on the ground around a tree below the tips of the outermost branches of the tree. Diaphragm emitter – emitters that contain a stretched membrane with a small opening. When particles plug the opening, pressure builds stretching the membrane until the particle is forced out. The membrane and opening then return to normal size. Emitter – a dispensing device in a micro-irrigation system that regulates the flow of water released to the soil at the plant’s roots. Emitters are sold by flow rates and typically are ½, 1, 2 and 4 gph. They may be found as high as 5, 7, 12, 18 and even 24 gph. Filter – a canister device with a screen of a specified mesh to catch particles large enough to clog emitters. Fittings – the array of coupling and closure devices used to construct a drip system including connectors, tees, elbows, goof plugs and end caps. Fittings may be of several types including compression, barbed and locking. Flow – the rate or amount of water that moves through pipes in a given period of time. Flow is expressed in gph, gallons per hour with micro-irrigation (drip) devices as opposed to the gpm, gallons per minute rate used for high-pressure sprinkler systems. Goof plugs – insertable caps to plug holes in mainline and microtubes where drip devices have been removed or aren’t needed.

Mainline – tubing used in the drip system and is sometimes called lateral line. It is a soft polyethylene material and comes in ½ or ¾ inch diameters. Micro-irrigation – an updated term adopted by the American Society of Agricultural Engineers for drip or trickle irrigation that also includes micro-spray and other new devices operating at low pressures. Water is applied frequently just above, on or below the surface of the soil at low flow rates with the goal of placing a quantity of water in the root zone that nearly approximates the consumptive use of the plant. Microspray – a low pressure sprayer device generally placed on a stake that is designed to wet soil with a fan or jet of water. Microtubes (spaghetti tubes) – the ¼ inch flexible pipe used to link emitters or sprayers to the mainline. Plastic stakes are frequently used to hold the tubes and the dispensing device attached to the end in place. Mister – a device that delivers fog-like droplets of water often for cooling purposes. Pressure – the force propelling water through pipes. Common household static (non-flowing) pressure is 50 to 70 psi (pounds per square inch). Irrigation systems operate under dynamic (flowing) water pressure that is reduced with elevation gain and friction loss through rubbing on the sides of pipes. Long lengths of pipe generally result in low pressure at the ends of the run. Divide a large irrigation zone into smaller ones, minimize attached components, or choose larger diameter pipe to assure adequate dynamic operating pressures. Pressure-compensating emitter – an emitter designed to maintain a constant output (flow) over a wide range of operating pressures and elevations. Pressure-sensitive emitter – an emitter that releases more water at the higher pressures and less at lower pressures found with long mainlines or terrain changes. Pressure regulator – a device that reduces incoming water pressure for low-pressure drip systems. Typical household water pressure is 50 to 60 psi while drip systems are designed to operate at around 20 to 30 psi depending on the manufacturer. Turbulent flow emitter – emitters with a series of channels that force water to flow faster not allowing particles to settle out and plug the emitter. Zone – the section of an irrigation system that can be operated at one time by means of a single control valve.

Emitters or drippers: These are devices used to control the discharge water from the lateral to the plants. They are usually spaced more than 1 meter apart with one or more emitters used for a single plant such as a tree. For row crops more closely spaced emitters may be used to wet a strip of soil. The aspect of an emitter that should be kept in mind to decide its efficiency is that it should provide a specified constant discharge which doesn’t vary much with pressure change and doesn’t block easily. Emission devices The actual application of water in a micro- irrigation system is through an emitter. The emitter is a metering device made from plastic/brass or other material that delivers a small but precise discharge. The quantity of water delivered from these emitters is usually expressed in volume flow per time units (i.e. L/h, L/min, m3 /h etc.). These emitters dissipate water pressure through the use of long-paths, small orifices or diaphragms. Some emitters are pressure compensating meaning they discharge water at a constant rate over a range of pressures known as pressure compensating drippers. Emission devices deliver water in three different modes: drip, bubbler and micro-sprinkler. In drip mode, water is applied as droplets or trickles. In bubbler mode, water `bubbles out' from the emitters. Water is sprinkled, sprayed, or misted in the micro-sprinkler mode. Emitters for each of these modes are available in several discharge increments. Some emitters are adapted to apply water to closely spaced crops planted in rows. Other emitters are used to irrigate several plants at once. There are emitters that can apply water to a single plant. Drip irrigation Depending on how the emitters are placed in the distribution line (mainly LDPE lines), the drip mode can be further delineated as a line source or a point source. The line source type emitters are placed internally in equally spaced holes or slits made along the line. Water applied from the close and equally spaced holes usually runs along the line and forms a continuous wetting pattern. This wetting pattern is suited for close row crops. The point source type emitters are attached external to the lateral pipe. The installer can select the desired location to suit the planting configuration or

place them at equally spaced intervals. Water applied from the point source emitter usually forms a round deep wetting spot. The point source wetting pattern is suited for widely spaced plants in orchards, vineyards and for landscape trees or shrubs. Types of Emitters An emitter is a device which applies water to the soil from the distribution system. The two major categories of emitters are point source and line source. Both categories have been successfully used in various cropping situations. There are numerous attributes sought in an optimum emitter. It should be available in small increments of discharge that is, on the order of 1 L/h. The flow should be controlled within narrow limits as a function of operating pressure to able to properly balance applied water with crop water use. A large flow area will be more resistant to clogging by particles which pass through the screening and filtration system or bacterial slime than a small flow area. The emitter should resist degradation due to temperature fluctuations and solar radiation, both of which are expected in typical installations. The manufacturer should specify a useful life for the emitter during which it will operate according to design specifications. This will allow the designer to make more accurate cost projections for system operation and will be useful in development of a maintenance and replacement schedule. Examples of different point and line source emitters are given in the following sections. Line source emitter Line source emitters are suitable for closely spaced row crops in fields and gardens. Line source emitters are available in two variations: A thin walled drip line has internal emitters molded or glued together at set distances within a thin distribution line (Figure 1a). The drip line is available in a wide range of diameters, wall thickness, emitter spacing and flow rates. The emitter spacing is selected to closely fit plant spacing for most row crops. The flow rate is typically expressed in gallons per minute (L/h). Drip lines are either buried below the ground or laid on the surface (Figures 1b). Burial of the drip line is preferable to avoid degradation from heat and ultraviolet rays and displacement from strong winds. However, some specialized equipment to install and extract the thin drip distribution line is required. The thick walled drip hose (Figure 2) is a robust variation of the thin walled drip line. The internal emitters are molded or glued to the drip hose. It is more durable because of its considerable thickness. The diameter of the drip hose is similar to that of the thin walled drip line. Unlike the thin wall drip line, the drip hose emitter spacing is wider and it operates at a higher pressure. The emitter discharges ranges from 0.75 to 7.5 L/h. Thick walled drip hose is typically laid on the ground and retrieved at the end of the cropping season. Point source emitters Point source emitters (Figure 3) are typically installed on the outside of the distribution line. Point source emitters dissipate water pressure through a long narrow path and a vortex chamber or a small orifice before discharging into the air. The emitters can take a predetermined water pressure at its inlet and reduce it to almost zero as the water exits. Some can be taken apart and manually cleaned. The typical flow rates range from 1 to 12 or more L/h. Bubbler irrigation Bubblers (Figure 4) typically apply water on a "per plant" basis. Bubblers are very similar to the point source external emitters in shape but differ in performance. Water from the bubbler head either runs down from the emission device or spreads a few inches

water through small orifices. Most bubbler emitters are marketed as pressure compensating. The bubbler emission devices are equipped with single or multiple port outlets. Most bubbler heads are used in planter boxes, tree wells, or specialized landscape applications where deep localized watering is preferable. The typical flow rate from bubbler emitters is between 7 and 75 L/h.