Methods of Irrigation ANGRAU PRASHANTH

8/3/2019 Methods of Irrigation ANGRAU PRASHANTH

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TERM PAPER ON

APPLICATION OF WATER METHODS OF IRRIGATION

SUBMITTED TO:

Dr. Praveen Rao,

Professor&Head,

Dept. of Agronomy,

College of Agriculture, Rajendranagar.

SUBMITTED BY:

Pasunoori Prashanth,

PhD Scholar,

I.D.NO. RAD/11-10,

Dept. of Agricultural Extension

Methods of Irrigation

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Scientific irrigation aims at efficient use of irrigation water in conjunction with

other essential inputs to enhance and sustain crop production. The manner in which

irrigation water is applied to the land is commonly referred to as method of irrigation.

Several irrigation methods are adopted towards this end under different circumstances.

Selection of appropriate irrigation method for any given combination of physical and

socioeconomic conditions involves numerous complex and often conflicting

considerations. Since, the economic considerations along with physical conditions and

cropping pattern are necessarily specific to each location; an irrigation system optimal

in a particular region may not be so in another. Applicability of a particular irrigation

method depends on several physical, human and economic factors.

Physical factors: Important physical factors associated with selection of irrigation

method include soils, crops, climate, topography, water quality and availability, depth of

water table, field size, maintenance and repairs.

Human and economic factors: Major factors involved are labour and management

skills, availability and cost, capital and energy costs in relation to expected returns.

Surface irrigation methods

In the surface methods of irrigation, water is applied directly to the soil surface

from a channel located at the upper reach of the field. Water may be distributed to the

crops in border strips, check basins or furrows. Two general requirements of prime

importance to obtain high efficiency in surface methods of irrigation are properly

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constructed water distribution systems to provide adequate control of water to the fields

and proper land preparation to permit uniform distribution of water over the field

Surface irrigation (gravity irrigation) is the most ancient method of irrigation

and this method still holds good for more than 95 per cent of the irrigated area in theworld. It can be defined as the process of introducing a stream of water at the head of a

field and allowing gravity and hydrostatic pressure to spread the flow over the surface

throughout the field. To move forward, the flowing water must have a downward slope

in the direction of flow. This is, generally, provided by running water over a sloping

land surface. The soil surface thus serves the dual role of water conveyance and

distribution. Field area nearest to the water inlet receives the greatest opportunity time

and hence the greatest depth of infiltration, whereas the down field farthest from inlet

receives least. This non uniformity is most pronounced in coarse (sandy) soils, in which

the infiltration rate is so high that much of the water entering the field infiltrates near

the inlet and relatively little water remain for farther reaches of the field. On the other

hand, fine textured soils (clayey) exhibit low infiltrability leading to significant flow of

applied water to the lower sections of field, while higher section (near the inlet) remains

insufficiently watered. The distribution of water is obviously affected by the slope and

length of run.

Water application efficiency is usually higher on fine textured (clayey) soils than

on coarse textured (sandy) soils because of their lower infiltration rates and more water

retention per unit depth within the root zone. However, clayey soils are more prone to

excessive wetness, compaction and impeded aeration. Land levelling and smoothing are

essential operations for successful surface irrigation. On regularly sloping lands, graded

long furrows and borders can significantly reduce levelling cost. Surface systems have

both advantages and disadvantages over others.

Advantages

• Initial capital investment for a surface irrigation system is, usually, lower

than for sprinkler or drip systems

• Surface irrigation systems have relatively low energy requirements in

routine operations

• Certain fruits and vegetables which can be damaged by sprinkling

because of leaf scorch from salt residue of sprinkled water can 'be safely irrigated

by surface systems

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• Surface systems can avoid wind drift and canopy interception losses

common in sprinkler irrigation

• Allows use of machinery for different operations

• Most important advantage of surface irrigation is its mechanical

simplicity and easy adaptation to small land holdings.

Disadvantages

• Costly and time consuming land preparation

• Low application efficiencies due, to wastage of water

• Water table raise and water logging

• Salinisation

1. WILD FLOODING

This is the primitive and least controlled of all the surface irrigation systems.

Water from the ditch is diverted to the upper part of the plot and allowed to spread over

the land in accordance with the natural topography.

After the water leaves the ditches, no attempt is made to control the flow. Hence,

it is called as wild flooding. Distribution of water is highly uneven. Consequently, part

of the area becomes waterlogged, while other part remains dry leading to uneven pattern

of crop growth. This method is applicable to inundation irrigation system or for pastures

or forage crops where water is not limiting or high value crops do not justify adoption

of better methods.

Advantages

Land not require precise land leveling and grading

Water application is quite easy and cheap

Skilled labour is not required

Disadvantages

Flooding is uncontrolled

Uniform wetting of land can not be achieved

Greater amount of water accumulates in lower spots

Excessive loss of water by percolation and run off may occur

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Sensitive crops may get damaged by excess water accumulation in lower parts

of the field.

2. Check basin irrigation

Check basin irrigation is the most common method of irrigation in India and in

many other countries. This is the simplest in principle of all methods of irrigation. There

are many systems in its use, but all involve dividing the field into smaller units so that

each has a nearly level surface. Ridges-are-constructed around the areas forming basins

within which the irrigation water can be controlled. The basins are filled to the desired

depth and the water is retained until it infiltrates into the soil. The depth of water may be

maintained for considerable periods of time by allowing the water to continue to flow

into the basins.

The distinguishing features of various uses of check basin method of irrigation

involve the size and shape of the basins and “whether irrigation is accomplished by

intermittent or continuous" collection of water in the basins. The ridges or bunds may be

temporary for a single irrigation as in the pre-sowing irrigation of seasonal crops. They

may be semi-permanently constructed for the repeated use in the case of paddy fields.

The size of ridge will depend on the depth of water to be impounded as well as on the

stability of the soil when wet.

Water is conveyed to the field by a system of supply channels and lateral field

channels. The supply channel is aligned on the upper side of the area and there is

usually one lateral channel for every two rows of check basins. Water from the laterals

is turned into the beds and is cut off when sufficient water has been administered into

the basin. Water is retained in the basin until it soaks into the soil. The size of the

irrigation stream is not critical as long as it is sufficient to provide coverage of the entire

strip in a relatively short time span required to apply the desired amount of water into

the soil. As the infiltration rate of soil increases, stream size must be increased or the

size of the basins reduced in order to cover the area within a short period of time. A

large size irrigation stream will permit a comparatively larger size of the basin.

The size of check basin may vary from one square metre, used for growing

vegetables and other intensive cultivation, to as large as two hectares or more, used for

growing rice under wet land conditions. When the land can be graded economically into

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nearly level fields, the basins are rectangular in shape. In rolling topography the ridges

follow the contours of the land surface. The contour ridges are connected by cross

ridges at intervals. The vertical interval between contour ridges usually varies from 6 to

12 cm. in case of upland irrigated crops like wheat and 15 to 30 cm in case of low land

irrigated crops .like rice.

Advantages

i.Since in this method the entire area is not flooded, it ensures -high water use

efficiency.

ii. Excessive seepage loss can be avoided by adopting this practice

iii. Damage to plants and loss of soil nutrients do not occur in this practice:..

Disadvantages

i. The major disadvantage of check basin method of irrigation is that the ridges interfere

with the movement of animal drawn or tractor drawn implements for inter culture

operations or harvesting of crops.

ii. Considerable land is occupied by ridges and lateral field channels and crop yields are

substantially reduced.

iii. The method impedes surface drainage.

iv. Precise land grading and shaping are required.

v. Labour requirement in land preparation and irrigation are much higher.

vi. Ridges interfere with the movement of animal-drawn or tractor-drawn implements

for interculture or harvesting of crops

vii. it is not suitable for irrigated crops which are sensitive to wet soil conditions around

the stems of' plants

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Soils, Land Topography: Check basin irrigation is suited to smooth gentle and uniform

land slopes and for soils havening moderate to slow infiltration rates. Steep slopes

require complex layouts and heavy land levelling.

Crops: Both row crops and close-growing crops are adapted to be used with basins as

long as the crop is not affected by temporary inundation or is planted in beds so that it

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will remain above the water level. The method is especially adapted to irrigation of

grain and fodder crops in heavy soils where water is absorbed very slowly and is

required to stand for a relatively long time to ensure adequate irrigation. It is also

suitable in very permeable soils which must be covered with water rapidly to prevent

excessive deep percolation losses at the upstream end.

Practically all irrigated paddy is grown in basins. Check basins are useful when

leaching is required to remove salts from the soil profile. The method enables the

conservation of rainfall and reduction in soil erosion by retaining a large part of the rain

in the basin to be infiltrated gradually, without loss due to surface runoff. The method

usually results in high water application and distribution efficiencies if the desired net

depth of irrigation can be estimated adequately and if the size of the irrigation stream is

measured properly. The low efficiencies obtained in check basin irrigation in India are

due to inadequate land levelling and uncontrolled water application.

In irrigating orchards, square to contour basins may be used as in other crops.

When the plants are widely spaced the ring method of basin irrigation is adopted. The

rings are circular basins formed around each tree. The ring basins are small when the

plant is young. The size is increased as the plant grows.

Check basin irrigation is suited to smooth, gentle and uniform land slopes and

for soils having moderate to slow infiltration rates. Steep slopes require complex layouts

and heavy land levelling. Both row crops as well as close growing crops are adapted to

basins as long as the crop is not affected by temporary inundation. The method is

especially adopted for, irrigation of grain and fodder crops in heavy, soils where water is

absorbed very slowly. It is also suitable in very permeable soils which must be covered

with water rapidly to prevent i excessive deep percolation loss of water at the upstream

end.

Ring basin irrigation: In irrigation orchards, square or contour basins may be used as in

other crops. When the plants are widely spaced the ring method of basin irrigation may

be adopted. The rings are circular basins formed around each tree. The ring basins are

small when the plant is young. The size is increased as the plant grows. An advantage of

the ring method is that the entire area is not flooded, thus obtaining high water use

efficiency. Usually there is one basin to a tree. In rectangular and contour basins,

however, however may be one basin to a single tree or two or more trees.

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Border strip method

The border method of irrigation makes use of parallel ridges to guide a sheet of

flowing water as it moves down the slope. The land is divided into a number of long

parallel strips called borders that are separated by low ridges. The border strip has little

or no cross slope but has a uniform gentle slope in the direction of irrigation. The

essential feature of border irrigation is to provide an even surface over which the water

can flow down the slope with a nearly uniform depth. Each strip is irrigated

independently by turning into a stream of water at the upper end. The water spreads andflows down the strip in a sheet confined by the border ridges. The irrigation stream must

be large enough to spread over the entire width between the border ridges without over

topping them. When the advancing water front either reaches the lower end, or a few

minutes before or after that, the stream is turned off. The water temporarily stored in the

border moves down the strip and infiltrates into the soil, thus completing the irrigation.

It is adapted to most soils where depth and topography permit, 1 the required land

leveling at a reasonable cost and without any permanent reduction in soil fertility. It is,

however, more suitable to soils having moderately low to moderately high infiltration

rates. It is generally not used in coarse sandy soils that have very high infiltration rates.

It is also not well suited to soils having a very low infiltration rate. This method is

suitable to irrigate all close growing crops like wheat, barley, fodder crops and legumes.

It is, however, not suitable for crops like rice which requires standing water during most

part of its growing season.

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Straight and contour borders

If the borders are constructed along the general slope of the field, they are

known as straight borders or slope borders, and if they are constructed across the

general slope of the field they are called contour borders. When fields can be levelled to

desirable land slopes economically and without affecting its productivity, graded

borders are easier to construct and operate. In case where land slope exceeds safe limit,

fields are undulating and levelling is not feasible, borders may be laid across the slope.

The design of a contour border is the same as that of a straight border. Each contour

border is level crosswise and has a uniform longitudinal gradient as in a straight border.

The width and length of a contour border are identical to that of a straight border for a

particular set of conditions.

In laying contour borders, the field is divided into a series of strips on the

approximate contour, and each strip is levelled as an independent area. Thus, a series of

strips are formed in successive elevations around the slope. The vertical interval

between the adjacent benches should, as far as possible, be limited to 30 cm, but should

not exceed 60 cm. The height of ridge should be sufficient to check both the normal

irrigation stream and run-off.

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Soils, Land Topography & wetting pattern: The border method of irrigation is

adapted to most soils where depth and topography permit the required land levelling at a

reasonable cost and without permanent reduction in soil productivity. It is, however,

more suitable to soils having moderately low to moderately high infiltration rates.

Usually it is not used in coarse sandy soils that have very high infiltration rates because

of the stringent limitations in design: It is also not well suited to soils having a very low

infiltration rate, since to provide adequate infiltration opportunity time, without surface

runoff at the lower end, the irrigation stream may be too small to completely over the

border strips.

The border method is suitable to irrigate all close growing crops like wheat,

barley, fodder crops and legumes. It is, however, not suitable for crops like rice which

requires standing water during most parts of its growing season.

Border Specifications and Stream Size

Successful operation of the border method requires that the system is designed

and operated properly. Proper design requires consideration of the hydraulics of flow in

borders which are described in the following article. However, some general

suggestions on width, length and slope of borders and size of irrigation streams are

presented in this article.

Width of border strip. The width of a border usually varies from 3 to 15 metres,

depending on the size of the irrigation stream available and the degree of land leveling

practicable. When the size of the irrigation stream available is small, the width is

reduced.' It is, however, not economical to keep the width less than about three metres;

as otherwise, too many ridges will have to be formed per unit area of the field surface.

Border length. The length of the border strip depends upon how quickly it can be

wetted uniformly over its entire length. This in turn depends on the infiltration rate of the soil, the slope of the land, and the size of the irrigation stream available. For

moderate slopes and small to moderate size irrigation streams, the following border

lengths are suggested:

Sandy and sandy loam soils: 60to 120 metres

Medium loam soils : 100 to 180 metres

Clay loam and clay soils : 150 to 300 metres

Border slope. The borders should have a uniform longitudinal gradient. Excessive

slopes will make the water run to the lower and quickly, causing insufficient

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irrigation at the upstream end and deep percolation losses and breach the bund at the

downstream. They also cause soil erosion in borders. On the other hand, too flat

slopes will result in the very slow movement of the border stream, causing deep

percolation losses at the upper reaches and inadequate wetting downstream.

Recommended safe limits of land slopes in borders are given below:

Sandy loam to sandy soils : 0.25% to' 0.60%

Medium loam soils : 0.20% to 0.40%

Clay to clay loam soils : 0.05% to 0.20%

Size of irrigation stream. The size of the irrigation stream needed depends on the

infiltration rate of the soil and the width of the border strip. Coarse textured soils with

high infiltration rates require large streams to spread water over the entire strip

rapidly and avoid excessive losses due to deep percolation at the upper reaches. Fine

textured soils with low infiltration rates require smaller streams to avoid excessive

losses due to runoff at the downstream end and deep percolation at the lower reaches.

Advantages

i. It is easy to construct border ridges even with some simple farm implements like a

bullock drawn A-frame ridger or tractor-drawn disc ridger.

ii. Labour requirement in irrigation is greatly reduced as compared to the conventional

check basin method of irrigation.

iii. Uniform distribution and high water application efficiencies are possible if the

system is properly designed.

iv. Large irrigation streams can be efficiently used.

v. Operation of the system is simple and easy.

vi. Adequate surface drainage is provided if outlets are available

Disadvantages

i. It requires an extensive land grading which is too expensive.

ii. It is mainly suitable for deep soils with the availability of large flow of water.

iii. Drainage may be essential.

iv. Water wastage is frequently observed.

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Furrow irrigation

The furrow method of irrigation is used in irrigation of row crops with furrows

developed between the crop rows in the planting and cultivating processes. The size and

shape of the furrow depends on the crop grown, equipment used and spacing betweencrop rows. Water is applied by running small streams in furrows between the crop rows.

Water infiltrates into the soil and spreads laterally to , irrigate the areas between the

furrows. The length of time water takes to flow in the furrows depends on .the amount

of water required to replenish root zone and the infiltration rate of the soil. Both large

and small irrigation streams can be used by adjusting the number of furrows irrigated at

anyone time to suit the available flow. In areas where surface drainage is necessary, the

furrows can be used to dispose off the run-off from rainfall rapidly.

Irrigation furrows may be classified into two general types is based on their

alignment. They are (i) straight furrows, (ii) contour furrows. Based on their size and

spacing furrows, may be classified as deep furrows and corrugation.

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a. Deep furrows

As mentioned above, deep furrows are of two types i.e. straight furrows and

contour furrows.

i. Straight furrows

Straight furrows, like borders, are laid down across the prevailing land slope. They are

best suited to sites where the land slope does not exceed 0.75 per cent. In areas of

intense rainfall, however, the furrow grade should not exceed 0.5 % so as to

minimisethe erosion hazard.

Straight furrows, like borders, are laid down the prevailing land slope. They are

best suited to sites where the land slope does not exceed 0.75 per cent. In areas of

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intense rainfall, however, the furrow grade should not exceed 0.5 per cent so as to

minimise the erosion hazard. The ranges in furrow slopes for efficient irrigation in

different soil types are the same as those recommended for borders.

In fine textured soils having very low infiltration rates, the furrows usually levellengthwise. With level furrows, the same stream size is maintained until the required

amount of water is applied. The water is ponded in the furrows until it is absorbed by

the soil.

ii. Contour furrows

Contour furrow method is similar to the graded furrow method in that the

irrigation water is applied in furrows, but the furrows carry water across the sloping

field rather than down the slope. Contour furrows are curved to fit the topography of the

land. The furrows are given gentle slope along its length as in the case of graded

furrows. Field supply channels rundown the land slope to feed the individual furrows

and are provided with erosion control structures.

Suitability to crops, soils and Land Topography:

Furrow irrigation can be used to irrigate all cultivated crops planted in rows, including

orchards and vegetables. Amongst the common cultivated crops of India, the method issuitable for irrigating maize, sorghum, sugarcane, cotton, tobacco, groundnut, potatoes,

and other vegetables. Furrows are particularly well adapted to irrigating, crops which

are subject to injury from pounded surface water or susceptible to fungal root rot.

Furrow irrigation is suitable, to most soils except sands that have a very high infiltration

rate and provide poor lateral distribution of water between furrows.

The furrow method maybe adapted to use, without erosion, on a wide range of natural

slopes by carrying the furrows across a slopping field rather than down the slope. The

method reduces labour requirements in land preparation and irrigation. Compared to

check basin method, there is no wastage of land in field ditches.

Furrow irrigation requires proper land grading. The land must be graded so that

water can travel the entire length of the row without ponding. This means that the high

and low spots must be removed and the land given enough slope to let the water flow

down the furrows. Once level, care in tillage operations can keep the land levelled.

Furrows can be spaced to fit the crops grown and the standard machines used for

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planting and cultivating. Crops like potatoes, maize and cotton have furrows between all

rows. Vegetable crops such as lettuce, carrots, and onions often have two or more rows

between furrows. Wide spaced crops, like melons, fruits trees and berries generally

require more than one furrow between crop rows. Furrows should be spaced close,

enough to ensure that water spreads to the sides into the ridge and root zone of the crop

before it moves down below the root zone.

In heavy black soils a combination of border strip irrigation with furrows is

usually preferred. These soils crack badly, so it is desirable to have furrows within the

border strips, so cracking will not allow the water to escape from furrow to furrow. The

border ridges are sufficiently large to confine the flow within the strip and the furrows

distribute it uniformly. Another advantage is that the furrows provide uniform drainage

during heavy monsoon rains and erosion is kept at a minimum.

Contour furrow method can be successfully used in nearly all irrigable soils. The

limitations of straight furrow irrigation are overcome by contouring to include sloping

lands. Light soils can be irrigated successfully across slopes up to 5 per cent. Where the

soils are stable and will not be cultivated (as in orchards), slopes up to eight to ten per

cent can be irrigated by contour furrowing. All row crops·, including grains, vegetables

and various cash crops, are adapted to this method.

The topography must be uniform enough to permit a head ditch that can feed the

entire area of contour-furrow. It must also be regular enough to permit installing a waste

ditch to carry off surplus irrigation water and rain water. Fields should be smoothed as

much as possible by land grading and by using a float, or land plane, before contour

plantings are laid out.

Contour-furrows for row crops are installed annually. But in orchards and other

permanent contour plantings, the same furrows and ditches are used every year, and

they may be considered as a permanent part of the water handling system. Furrows and

waste ditches should be cleaned out and prepared for the rainy seasons immediately

after crops are harvested.

Contour furrows may be used on most soil types, except on light sandy soils and

soils that crack. The ridges between furrows in sandy soils may break and wash out,

overloading the furrow below, which also breaks. This may continue all the way down

the slope causing heavy erosion damage. Soils that crack provide channels for water,

causing similar down slope furrow breaks. Hence their use is limited on steep slopes in

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sandy soils and heavy black soils.

In heavy rainfall areas the length of furrows should be short enough to dispose

off the runoff safely without breaking the furrows. Erosion control structures are needed

to carry the surplus water down the slope. Contour furrow irrigation .used inconjunction with contour bunding and terracing provides an insurance against furrow

breaks. Land which is too steep for contour furrows may sometimes be graded to

levelled strips (bench terraces) across the slope on which the furrows can be

constructed. Land with slopes upto 25 per cent or more can be benched to permit the

production of irrigated crops.

Advantages

i. Water in the furrows contacts only one half to one fifth of the land surface, therebyreducing puddling and crusting of the soil, and evaporation losses.

ii. Early sowing is possible which is a distinct advantage in heavy soils.

iii. It can be safely adopted on the sloppy lands by opening the furrows across the slope.

iv. This .method reduces labour requirement in land preparation and Irrigation.

v. Compared to check basin method, there is no wastage of land in field ditches.

Disadvantages

i. It requires skilled labourers to operate. .

ii. It may cause serious erosion, if excess water flows over the ridges.

iii. Difficult to carry on mechanical operations.

iv. Water in the furrows contacts only one-half to one-fifth of the land surface, thereby

reducing puddling, and crusting of the soil, and evaporation losses

v. Earlier cultivation is possible which is distinct advantage in heavy soils.

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Methods of Irrigation ANGRAU PRASHANTH

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