Chapter 5 methods of irrigation Dr. Thomas Abraham_19-3-14

AMBO UNIVERSITYINSTITUTE OF TECHNOLOGY

Department of Agricultural & Bioprocess Engineering

Principles of Irrigation & Drainage(Course Code : ABPE 462)

Chapter-5

Irrigation Methods

By Dr. Thomas Abraham

(Associate Professor, Dept. of ABPE

[email protected]

+251-938607569)

Irrigation Methods are mainly classified into :

1. Surface Irrigation or Gravity Irrigation 2. Subsurface Irrigation or Sub-irrigation 3. Sprinkler or overhead irrigation 4. Drip or Trickle irrigation

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Chapter-5

Irrigation Methods

1) SURFACE IRRIGATION Irrigation water flows across the field to the point of

infiltration Primarily used for field crops and orchards Water is applied to the soil surface and the water flows

by gravity either through furrows, strips or basins. Water is applied from a channel located at the upper

reach of the field. Loss of water by conveyance and deep percolation is

high and the efficiency of irrigation is only 40-50% at field level in surface method of irrigation.

Properly constructed water distribution systems to give sufficient control of water to the fields

And effective land preparation to permit uniform distribution of water over the field are very important.

Various Methods of Irrigation

SURFACE IRRIGATION Water is applied to the field in either the controlled or

uncontrolled manner. Controlled: Water is applied from the head ditch and

guided by corrugations, furrows, borders, or ridges. Uncontrolled: Wild flooding. Surface irrigation is entirely practised where water is

abundant. Low initial cost of development is later offset by high

labour cost of applying water. Deep percolation, runoff and drainage problems

1. Furrow irrigation

2. Border irrigation

3. Basin irrigation

Common types of surface irrigation

1.Furrow irrigation

Furrow irrigation - in which the water poured on the field is directed to flow through narrow channels dug between the rows of crops, instead of distributing the water throughout the whole field evenly.

The furrows must all have equal dimensions, in order to guarantee that the water is distributed evenly.

Like flood irrigation, furrow irrigation is rather cheap in areas where water is inexpensive.

Furrow irrigation

Furrow Irrigation In furrow irrigation, only a part of the land

surface (the furrow) is wetted thus minimizing evaporation loss.

Irrigation can be by corrugation using small irrigation streams.

Furrow irrigation is adapted for irrigating on various slopes except on steep ones because of erosion and bank overflow.

Furrow Irrigation (Contd.)

There are different ways of applying water to the furrow. As shown in Fig 3.1, siphons are used to divert water

from the head ditch to the furrows. There can also be direct gravity flow whereby water is

delivered from the head ditch to the furrows by cutting the ridge or levee separating the head ditch and the furrows.

Gated pipes can also be used. Large portable pipe(up to 450 mm) with gate openings spaced to deliver water to the furrows are used.

Water is pumped from the water source in closed conduits.

The openings of the gated pipe can be regulated to control the discharge rate into the furrows.

Furrow Irrigation by Cutting the Ridge

Furrow Irrigation with Siphons

Fig. 3.1: A Furrow System

Shape of furrows mainly depends on the type of soil and the size of the stream- Deep, narrow V-shaped furrow - suitable for sandy soil

Figure: Wide, shallow furrow suitable for clay soil

Design Parameters of Furrow Irrigation

The Major Design Considerations in Surface Irrigation Include:

Storing the Readily Available Moisture in the Root Zone, if Possible;

Obtaining As Uniform Water Application As Possible; Minimizing Soil Erosion by Applying Non-erosive

Streams; Minimizing Runoff at the End of the Furrow by Using

a Re-use System or a Cut -Back Stream; Minimizing Labour Requirements by Having Good

Land Preparation, Facilitating Use of Machinery for Land Preparation,

Cultivation, Furrowing, Harvesting Etc.

Furrow Irrigation Contd. The Specific Design Parameters of Furrow

Irrigation Are Aimed at Achieving the Above Objectives and Include:

a) Shape and Spacing of Furrows: Heights of ridges vary between 15 cm and 40 cm and the distance between the ridges should be based on the optimum crop spacing modified, if necessary to obtain adequate lateral wetting, and to accommodate the track of mechanical equipment.

The range of spacing commonly used is from 0.3 to 1.8 m with 1.0 m as the average.

Design Parameters of Furrow Irrigation Contd. d) Field Slope: To reduce costs of land

grading, longitudinal and cross slopes should be adapted to the natural topography.

Small cross slopes can be tolerated. To reduce erosion problems during rainfall,

furrows (which channel the runoff) should have a limited slope (see Table 3.1).

Table 3.1 : Maximum Slopes for Various Soil Types

Soil Type Maximum slopes* Sand 0.25 Sandy loam 0.40 Fine sandy loam 0.50 Clay 2.50 Loam 6.25

Source: Withers & Vipond (1974) *A minimum slope of about 0.05 % is required to

ensure surface drainage.

Border Irrigation

Border Irrigation

In this, Parallel ridges are made to guide a sheet of flowing water when the water moves down the slope.

The field is divided into several long parallel strips called borders that are separated by low ridges.

Field should be even surface over which the water can flow down the slope with a nearly uniform depth.

Every strip is independently irrigated by turning a stream of water at the upper end.

Then water spreads and flows down the strip in a thin sheet. Water moves towards the lower end without erosion

covering the entire width of the border. Sufficient moisture is provided to the soil to entire length of

the border. Border method is suitable for most of the soils, while it is

best suited for soils having moderately low to high infiltration rates.

However, it is not suitable for course sandy and clay textured soils.

1. Border Irrigation

Border Irrigation System

In a border irrigation, controlled surface flooding is practised whereby the field is divided up into strips by parallel ridges or dykes and each strip is irrigated separately by introducing water upstream and it progressively covers the entire strip.

Border irrigation is suited for crops that can withstand flooding for a short time e.g. wheat.

It can be used for all crops provided that the system is designated to provide the needed water control for irrigation of crops.

It is suited to soils between extremely high and very low infiltration rates.

Border Irrigation System

Border Irrigation

Border Irrigation Contd.

In border irrigation, water is applied slowly. The root zone is applied water gradually

down the field. At a time, the application flow is cut-off to

reduce water loses. Ideally, there is no runoff and deep

percolation. The problem is that the time to cut off the

inflow is difficult to determine.

2. Basin Irrigation

Basin method of irrigation is adopted mainly in orchards.

Usually round basins are made for small trees and square basin for large trees.

These basins allow more water to be impounded as the root zones of orchard plants are usually very deep.

Each basin is flooded and water is allowed to infiltrate into the soil.

Based on type of crop and soil, nearly 5-10 cm depth of water may be needed for every irrigation.

The advantage of basin method is that unskilled labour can be used as there is no risk of erosion.

Disadvantages : there is difficulty in using modern machinery and it is also labour intensive.

2. Basin Irrigation

Basin irrigation is suitable for many field crops. Rice grows best when its roots are submerged in

water and so basin irrigation is the best method to use for this crop.

Other crops which are suited to basin irrigation include:

Pastures, e.g. alfalfa, clover; Citrus, banana; Crops which are broadcast, such as cereals, and To some extent row crops such as tobacco.

Suitable crops

Basin Irrigation Diagram

I

rrigation time.

Size of Basins The size of basin is related to stream size and soil type(See

Table below). Table : Suggested basin areas for different soil types and rates of water flow Flow rate Soil Type Sand Sandy loam Clay loam Clay l/s m3 /hr .................Hectares................................ 30 108 0.02 0.06 0.12

0.20 60 216 0.04 0.12 0.24

0.40 90 324 0.06 0.18 0.36

0.60 120 432 0.08 0.24 0.48

0.80 150 540 0.10 0.30 0.60

1.00 180 648 0.12 0.36 0.72

1.20 210 756 0.14 0.42 0.84

1.40 240 864 0.16 0.48 0.96

1.60 300 1080 0.20 0.60 1.20

2.00 Note: The size of basin for clays is 10 times that of sand as the infiltration rate for clay is low

leading to higher irrigation time. The size of basin also increases as the flow rate increases. The table is only a guide and practical values from an area should be relied upon. There is the need for field evaluation.

Most common among surface irrigation Suitable for close growing crops like

groundnut, wheat, finger millet, pearl millet, paragrass etc.

In this method field is divided into small plots surrounded by bunds on all four sides.

Water from head channel is supplied into the field channel one after the other.

Each field channel supplies water to two rows of check basins and water is applied to one basin after other.

Check basin Method

In this, field is laid out into long, narrow, strips, bordering with small bunds.

Most common size of strips are 30-50 m length and 3-5 m width.

Borders are laid out along the general slope.

Water from the channel is allowed into each strip at a time.

This method is suitable for close growing crops and medium to heavy textured soils.

Not suitable for sandy soils.

Border Strip Method

It should be applied only to flat lands that do not concave or slope downhill so that the water can evenly flow to all parts of the field.

Yet even so, about 50% of the water is wasted and does not get used by the crops.

Some of this wasted water accumulates at the edges of a field and is called run-off.

In order to conserve some of this water, growers can trap the run-off in ponds and reuse it during the next round of flood irrigation.

Flood irrigation

In flood irrigation, a large amount of water is brought to the field and flows on the ground among the crops.

In regions where water is abundant, flood irrigation is the cheapest method

This low tech irrigation method is commonly used by societies in developing countries.

Flood irrigation

However a large part of the wasted water can not be reused due to massive loss via evaporation and transpiration.

One of the advantages of flood irrigation is its ability to flush salts out of the soil, which is important for many saline intolerant crops.

However, the flooding causes an anaerobic environment around the crop which can increase microbial conversion of nitrogen from the soil to atmospheric nitrogen, or denitrification, thus creating low nitrogen soil.

Surge flooding is an attempt at a more efficient version of conventional flood irrigation in which water is released onto a field at scheduled times, thus reducing excess run-off.

Flood irrigation

- Irrigation to crops by applying water from beneath the soil surface either by constructing trenches or installing underground perforated pipe lines.

In this system, water is discharged into trenches.

And allowed to stand during the whole period of irrigation for lateral and upward movement of water by capillarity to wet the soil between the trenches.

1.2. Subsurface or subirrigation

Conditions that favor subsurface irrigation An impervious subsoil at a depth of 2 m or more. A very permeable subsoil of reasonably uniform texture

permitting good lateral and upward movement of water. Permeable loam or sandy loam surface soil. Uniform topographic conditions and moderate slope. Existence of high water table. Irrigation water is scarce and costly. Soils should be free of any salinity problem. It must be ensured that no water is lost by deep

percolation. Subsurface irrigation is made by constructing a series of

ditches or trenches 60 to 100 cm deep. Width of the trenches is about 30 cm and vertical. Spacing between the trenches varies between 15 to 30 m

depending on soil types and lateral movement of water in soils.

Subsurface or subirrigation (cont..)

Various types of crops, particularly with shallow root systems are well adapted to subsurface irrigation system.

Wheat, potato, beet, peas, fodder crops etc.

Advantages Maintenance of soil water at favorable tension Loss of water by evaporation is held at

minimum Can be used for soils with low water holding

capacity and high infiltration rate where surface irrigation methods cannot be adopted and sprinkler irrigation is expensive.

Suitable crops

Presence of high water table. Poor quality irrigation water cannot be used-good quality water must be available.

Chances of saline and alkali conditions being developed by upward movement of salts with water.

Soils should have a good hydraulic conductivity for upward movement of water.

Limitations

Sprinkler irrigation is a method of applying irrigation water which is similar to natural rainfall.

Water is distributed through a system of pipes usually by pumping.

Water under pressure is carried and sprayed into the air above the crop through a system of:

Overhead perforated pipes, nozzle lines, or through nozzles fitted to riser pipes attached to a system of pipes laid on the ground.

Nozzles of fixed type or rotating under the pressure of water are set at suitable intervals in the distribution pipes.

Sprayed water wets both the crop and the soil and, hence, has a refreshing effect.

Water is applied at a rate less than the intake rate of soil so that there is no runoff.

Measured quantity of water is applied to meet the soil water depletion.

5.3. Sprinkler irrigation

Sprinkler irrigation is suited for most row, field and tree crops and water can be sprayed over or under the crop canopy.

Large sprinklers are not recommended for irrigation of delicate crops such as lettuce because the large water drops may damage the crop.

Suitable slopes Sprinkler irrigation is adaptable to any farmable

slope, whether uniform or undulating. Lateral pipes supplying water to the sprinklers

should always be laid out along land contour. This will minimize the pressure changes at the

sprinklers and provide a uniform irrigation.

Suitable crops

Sprinklers are best suited to sandy soils with high infiltration rates although they are adaptable to most soils.

Application rate from the sprinklers (in mm/hour) is always chosen to be less than the basic infiltration rate of the soil - so that surface ponding and runoff can be avoided.

Sprinklers are not suitable for soils which easily form a crust.

Suitable soils

A typical sprinkler irrigation system consists of the following components:

Pump unit Mainline Laterals Sprinklers   Suitable irrigation water A good clean supply of water, free of

suspended sediments, to avoid problems of sprinkler nozzle blockage and spoiling the crop by coating it with sediment.

Sprinkler System Layout

Components of Sprinkler Irrigation

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Sprinkler irrigation (cont..)

• Uniform application by “artificial rain”

• Good application efficiencies (0.7 – 0.8) – dependent on wind, temperature, humidity

• Fairly terrain independent (but design must take terrain into account)

• Can have a low labour content

However,

• High(ish) investment cost

• High maintenance cost due to pumping

• Can be complex to run

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Sprinkler irrigation: Criteria

• Must permit cost recovery within one to two years (and double investment in a short time)

• Must be suitable for use on small and irregular shaped plots

• Must require only simple maintenance and tools

• Have a low risk of component failure

• Be simple to operate

• Be durable and reliable – able to withstand rough and frequent handling without serious damage

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Sprinkler irrigation: System layout

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Sprinkler irrigation

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Sprinkler irrigation: Drag hose system

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Sprinkler

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Sprinkler irrigation: Spray pattern

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Sprinkler irrigation: Spray pattern

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Sprinkler Spray pattern: Variation in pressure

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Sprinkler irrigation: Variation in pressure

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Sprinkler irrigation: Hand move laterals

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Sprinkler irrigation: Drag hose system

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Sprinkler irrigation: Drag hose system

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Sprinkler irrigation: Centre pivot system

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Sprinkler irrigation: Centre pivot system

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Sprinkler irrigation: Centre pivot system

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Sprinkler irrigation: Centre pivot system

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Sprinkler irrigation: Linear move system

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Sprinkler irrigation: Linear move system

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Sprinkler irrigation: Linear move system

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Sprinkler irrigation: Mobile Raingun

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Sprinkler irrigation: Mobile Raingun

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Sprinkler irrigation: Appropriateness

Type Score Crops

Piped distribution 16 All

“Low tech” 16 All

Drag hose 15 All

Solid set 14 Orchards

Hand move laterals 12 All

Perforated pipe 11 Soft fruit and veg

Static gun 10 Cereals, Row crops

Side roll 7 Short cereals, row crops

Traveling gun 7 Cereals, Row crops

Boom 6 Cereals, Row crops

Centre pivot 5 Cereals, Row crops

Linear move 5 Cereals, Row crops

Side move 4 Cereals, Row crops

Raingun Irrigation System

Linear Move

Centre Pivot

Pivot of a Centre Pivot System

System Layout

Layout is determined by the Physical Features of the Site e.g. Field Shape and Size, Obstacles, and topography and the type of Equipment chosen.

Where there are several possibilities of preparing the layout, a cost criteria can be applied to the alternatives.

Laterals should be as long as site dimensions, pressure and pipe diameter restrictions will allow.

Laterals of 75 mm to 100 mm diameter can easily be moved.

Etc. - See text for other considerations

Design of Laterals

Laterals supply water to the Sprinklers Pipe Sizes are chosen to minimize the pressure

variations along the Lateral, due to Friction and Elevation Changes.

Select a Pipe Size which limits the total pressure change to 20% of the design operating pressure of the Sprinkler.

This limits overall variations in Sprinkler Discharge to 10%.

Lateral DischargeThe Discharge (QL) in a Lateral is

defined as the flow at the head of the lateral where water is taken from the mainline or submain.

Thus: QL = N. qL Where N is the number of sprinklers on the lateral and qL is the Sprinkler discharge (m3/h)

Selecting Lateral Pipe Sizes

Friction Loss in a Lateral is less than that in a Pipeline where all the flow passes through the entire pipe Length because flow changes at every sprinkler along the Line.

First Compute the Friction Loss in the Pipe assuming no Sprinklers using a Friction Formula or Charts and then:

Apply a Factor, F based on the number of Sprinklers on the Lateral.

Pressure at Head of Lateral

The Pressure requirements (PL)where the Lateral joins the Mainline or Submain are determined as follows:

PL = Pa + 0.75 Pf + Pr For laterals laid on Flat land

PL = Pa + 0.75 (Pf Pe) + Pr For Laterals on gradient.

The factor 0.75 is to provide for average operating pressure (Pa) at the centre of the Lateral rather than at the distal end. Pr is the height of the riser.

Pumping Requirements

Maximum Discharge (Qp) = qs N Where:

qs is the Sprinkler Discharge and N is the total number of Sprinklers operating at

one time during irrigation cycle. The Maximum Pressure to operate the system

(Total Dynamic Head, Pp) is given as shown in Example.

DRIP OR TRICKLE IRRIGATION

3.4.1 Introduction: In this irrigation system: i) Water is applied directly to the crop ie. entire field is

not wetted. ii) Water is conserved (iii) Weeds are controlled because only the places

getting water can grow weeds. (iv) There is a low pressure system. (v) There is a slow rate of water application somewhat

matching the consumptive use. Application rate can be as low as 1 - 12 l/hr.

(vi) There is reduced evaporation, only potential transpiration is considered.

vii) There is no need for a drainage system.

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 (Figure 60 in Notes).

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.

Trickle or drip irrigation (cont…)

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Drip irrigation: Layout

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Drip Irrigation System

• 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.

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Water Use for Trickle Irrigation System

• 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.

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Micro irrigation: Drip irrigation

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Micro irrigation: Root zone

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Micro irrigation: Infiltration

Sandy soil Clay soil

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Micro irrigation: Emitters

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Micro irrigation: Thick walled drip hose

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Micro irrigation: Thin walled drip hose

Drip Irrigation System

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.

Drip Irrigation

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 crops

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 slopes

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 soils

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.

Suitable irrigation water

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

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A typical drip irrigation system is shown in Figure 61 and consists of the following components:

Pump unitControl headMain lineLateralsEmitters or drippers. 

Drip System Layout

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.

Drip irrigation components

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.

Mainlines and laterals

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.

Cont…

Water Use for Trickle Irrigation System Contd. Karmeli and Keller (1975) suggested the following water use rate for trickle irrigation design ETt = ET x P/85   Where: ETt is average evapotranspiration rate for crops under

trickle irrigation; P is the percentage of the total area shaded by crops; ET is the conventional evapotranspiration rate for the crop. E.g.

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.

Emitters

Consist of fixed type and variable size types. The fixed size emitters do not have a mechanism to compensate for the friction induced pressure drop along the lateral while the variable size types have it.

Emitter discharge may be described by: q = K h x

Where: q is the emitter discharge; K is constant for each emitter ; h is pressure head at which the emitter operates and x is the exponent characterized by the flow regime.

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 Concluded 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.

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.

SUB-SURFACE IRRIGATION (Contd…) 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.