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IRRIGATION

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Definition

Irrigation may be defined as the process of

artificially supplying water to soil for full-fledged

nourishment of the crops.

In other words, it is the science of artificial

application of water to the land in accordance

with the 'crop requirements' throughout the

'crop period'.

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NECESSITY OF IRRIGATION

Scanty RainfallIn India, many areas like Rajasthan receives very less rainfall. These areas

need irrigation water, in such cases, irrigation works may be constructed at

the places where quantity of water is available and we can convey the water

to such areas where there is deficiency of water.

Non-Uniform Rainfall

In India, there is large spatial and temporal variation in precipitation. Thus,the rainfall is not uniform at all the zones. The rainfall during the winter is

very scanty and therefore rabi crops need the artificial supply of water by

the irrigation works.

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Increasing Yield in Dry Farming

Dry farming depends upon natural rainfall agriculture which deals with

rainfall only is called dry farming.

Practicing Crop Rotation

To bring in rotation of crops, i.e. if we want that the more number of crops

should be rotated then there, will be need of irrigation water.

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Controlled Water supply

As irrigation serves the following important purposes :

(a) It can save the crops from drying during short duration

droughts.(b) It washes out or dilutes salts in soil.

(c) It cools the soil and also the atmosphere and makes more

favorable environment for healthy plant growth

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In general, necessity of irrigation

1.inadequate rainfall

2.increasing yield of crops

3.growing perennial crops4.uneven distribution of rainfall

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EFFECTS OF IRRIGATION

Advantages of irrigation

1.increase in food production

2.optimum benefits3.general prosperity

4.afforestation.

5.Inland navigation6.Domestic water supply

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Disadvantages Of Irrigation

(a) Wasteful use of water

(b) Water logging

(c) Soil degradation in irrigated areas

(d) Contamination of water with harmful substances

(e) Damp climate and Ecological imbalances

( f ) Mosquitoes breeding

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sources of water

Surface water: It may be by flowing river or

from still waters of tanks, ponds, lakes, pools

or artificial reservoirs such as dams, barrages

and diversionary bunds with different storage

capacity.

Ground water: Water stored in the

underground is known as groundwater.

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Planning concepts of irrigation

schemesIrrigation projects in India are classified into three categoriesmajor medium &minor according to the area cultivated the classification criteria is as follows:-

1)Major irrigation projects: projects which have a culturable command area(CCA) of more than 10,000 ha but more than 2,000 ha utilize mostly surfacewater resources.

2) Medium irrigation projects: projects which have CCA less than 10,000 ha.But more than 2,000 ha utilizes mostly surface water resources.

3) Minor irrigation projects: projects with CCA less than or equal to 2,000 ha.utilizes both ground water and local surface water resources. Ground waterdevelopment is primarily done through individual and cooperative effort offarmers with the help of institutional finance and their own savings.

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Irrigation may broadly be classified into :

(a) Surface Irrigation- In this type of irrigation

water wets the soil surface

(b) Sub-surface irrigation-In this type of irrigation,

water does not wet the soil surface water comes

directly in touch with root zone of the crops,

IRRIGATION SYSTEMS

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1. Flow irrigation system: where the irrigation water is conveyed tothe irrigated land. This may again be classified into the following.

Direct irrigation: Where the irrigation water is obtained directly fromthe river, without any intermediate storage. This type of irrigation ispossible by constructing a weir or a barrage across a river to raise thelevel of the river water and thus divert some portion of the river flowthrough an adjacent canal, where the flow takes place by gravity.

Reservoir/tank/storage irrigation: The irrigation water is obtainedfrom a river, where storage has been created by construction anobstruction across the river, like a dam. This ensures that even whenthere is no inflow into the river from the catchment, there is enoughstored water which can continue to irrigate fields through a system ofcanals.

Surface Irrigation

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2. Lift irrigation system:Where theirrigation water is available at a level lower

than that of the land to be irrigated and

hence the water is lifted up by pumps or byother mechanical devices for lifting water

and conveyed to the agricultural land

through channels flowing under gravity

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Flow irrigation can be further subdivided into :

(a) Perennial irrigation

(b) Flood irrigation

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Perennial Irrigation

In this type of irrigation system, the waterrequirement for irrigation is supplied constantly

and continuously in accordance with croprequirements throughout the crop period.

In this system of irrigation, water is suppliedthrough the storage canal head works and canaldistribution system.

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Perennial canal system may be further sub-divided as follows :Direct Irrigation

When irrigation is done from direct run off of a river, or by diverting

the river run off water into some canal by constructing a diversion

weir or barrage across the river. For example, Ganga Irrigation canal

system.Storage Irrigation

When a dam is constructed across a river to store water during the

monsoon and the stored water is supplied in the off taking channels

during periods of low flow, it is called storage irrigation. For example,Ram Ganga dam project in UP. In coastal areas where rivers are not

perennial storage irrigation becomes a necessity. However, It is more

costly and difficult to construct.

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Flood Irrigation

This kind of irrigation is some times called as

Inundation irrigation.

In this method of irrigation soil is kept

submerged and flooded with water, so as to

cause thorough saturation of the land.

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Sub-surface Irrigation

In this system of irrigation the supplied water comes directly

in touch with root zone of the crops. This system of irrigation

may be employed usefully under the following conditions

(a) Topography conditions of area are uniform.

(b) Land slope is moderate.

(c) The quality of irrigation water is good.

(d) The soil in the roof zone is permeable in nature.

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Sub surface irrigation may be classified into two types

(a) Natural sub irrigation, and

(b) Artificial sub irrigation.

Natural Sub-irrigation

When underground irrigation can be achieved simply by natural processes.without any extra efforts it is called natural sub-Irrigation. In fact leakage

water from channel, etc. goes underground and during seepage through the

sub soil, it may irrigate the crop in the lower lands

Artificial Sub-irrigationThe open jointed system of drain is artificially laid below the soil so as to

supply the water to the crop by capillary action, then it is known as artificial

sub-irrigation. This process is not adopted in India because it is very costly.

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Modes of irrigation

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Border strip method

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In border strip irrigation, uses land formed into stripswhich are leveled across the narrow dimension, i.e. widthbut sloping along the long dimension, i.e. length, areformed.

Ridges or borders bound these strips. A border strip canbe formed as straight one or along the contour.

Accordingly border strip irrigation may be classified asstraight or contour.

During irrigation, water is turned into the upper end ofthe border strip, and advances down the strip.

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FURROW IRRIGATION

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Furrows are small channels, which carry water downthe land slope between the crop rows. Water infiltratesinto the soil as it moves along the slope. The crop isusually grown on ridges between the furrows

Water is applied to the furrows by letting in water fromthe supply channel, either by pipe siphons or bymaking temporary breaches in the supply channel

embankment. The length of time the water is to flow inthe furrows depends on the amount of water requiredto replenish the root zone and the infiltration rate of thesoil and the rate of lateral spread of water in the soil.

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Basin Irrigation

Basins are flat areas of land surrounded by low bunds.The bunds prevent the water from flowing to theadjacent fields. The basins are filled to desired depthand the water is retained until it infiltrates into the soil.Water may be maintained for considerable periods of

time

Basin method of irrigation can be formally divided intotwo, viz; the check basin methodand the ring basinmethod. The check basin method is the mostcommon method of irrigation used in India. In thismethod, the land to be irrigated is divided into smallplots or basins surrounded by checks, levees (lowbunds);

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Sprinkler irrigation

In the sprinkler method of irrigation, water is appliedabove the ground surface as spray. The spray isdeveloped by the flow of water under pressure throughsmall orifices or nozzles. The pressure is obtained bypumping with careful selection of nozzle sizes, operating

pressures and sprinkler spacing. High efficiency in waterapplication/distribution can be obtained with sprinklersystem.

Sprinkler systems are of generally two major typesviz. (i) rotating head system, and (ii) perforated pipesystem.

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Drip irrigation

As the name signifies, drip irrigation, also termed astrickle irrigation, involves the slow application of water tothe root zone of a crop. The method was initiated inIsrael and is now being tried in other countries.

In this method, water can be used very economically,since loss due to deep percolation and surfaceevaporation are reduced to the minimum. This method,therefore, is highly suitable to arid regions and orchardcrops. The successful raising of orchards even on saline

soils has been made possible by the drip system ofirrigation. The system can also be used for applyingfertilizers in solutions

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HISTORICAL DEVELOPMENT ANDIRRIGATION IN INDIA THROUGH AGES

The history of irrigation development in India

can be traced back to prehistoric times. Vedas

and ancient Indian scriptures made reference

to wells, canals, tanks and dams which werebeneficial to the community and their efficient

operation and maintenance was the

responsibility of the State

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In a monsoon climate and an agrarianeconomy like India, irrigation has played amajor role in the production process. There isevidence of the practice of irrigation since the

establishment of settled agriculture during theIndus Valley Civilization (2500 BC). Theseirrigation technologies were in the form ofsmall and minor works, which could be

operated by small households to irrigatesmall patches of land and did not require co-operative effort

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The spread of agricultural settlements to

less fertile and irrigated area led to co-

operation in irrigation development and the

emergence of larger irrigation works in theform of reservoirs and small canals

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In the south, Cholas as early as secondcentury to provide irrigation from the Cauveryriver. Wherever the topography and terrain

permitted, it was an old practice in the regionto impound the surface drainage water intanks or reservoirs by throwing across anearthen dam with a surplus weir, where

necessary, to take off excess water, and asluice at a suitable level to irrigate the landbelow

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MEDIEVAL INDIA

In the medieval India, rapid advances also tookplace in the construction of inundation canals.Water was blocked by constructing bunds acrosssteams. This raised the water level and canalswere constructed to take water to the fields. Thesebunds were built by both the state and privatesources. Ghiyasuddin Tughluq (1220-250 iscredited to be the first ruler who encourageddigging canals. However, it is Fruz Tughlug (1351-

86) who inspired from central Asian experience, isconsidered to be the greatest canal builder beforethe nineteenth century

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Irrigation is said to be one of the major

reasons for the growth and expansion of

the Vijayanagar empire in southern India

in the fifteenth century. It may be notedthat, but for exceptional cases, most of the

canal irrigation prior to the arrival of the

British was of the diversionary nature

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Irrigation had also increased employmentopportunities and helped in the generation ofsurplus for the maintenance of the army andthe bureaucracy. As agricultural development

was the pillar of the economy, irrigationsystems were paid special attention to, asirrigation was seen to be a catalyst forenhanced agricultural production. This is

demonstrated by the fact that all the large,powerful and stable empires paid attention toirrigation development.

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British rule

Irrigation development under British rulebegan with the renovation, improvement andextension of existing works, like the onesmentioned above. When enough experienceand confidence had been gained, theGovernment ventured on new major works,like the Upper Ganga Canal, the Upper Bari

Doab Canal and Krishna and Godavari DeltaSystems, which were all river-diversion worksof considerable size.

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The recurrence of drought and famines during the second halfof the nineteenth century necessitated the development ofirrigation to give protection against the failure of crops and toreduce large scale expenditure on famine relief

Between the two types of works namely productive andprotective, the former received greater attention from theGovernment.

The gross area irrigated in British India by public works at theclose of the nineteenth century was about 7.5 M-ha Of this,4.5 M-ha came from minor works like tanks, inundation canalsetc. for which no separate capital accounts were maintained.The area irrigated by protective works was only a little morethan 0.12 M-ha

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AT THE TIME OF INDEPENDENCE

The net irrigated area in the Indian sub continent, comprising theBritish Provinces and Princely States, at the time of independencewas about 28.2 M-ha , the largest in any country of the world.

The partition of the country, however, brought about sudden anddrastic changes, resulting in the apportionment of the irrigated area

between the two countries; net irrigated area in India and Pakistanbeing 19.4 and 8.8 M-ha respectively.

Major canal systems, including the Sutlej and Indus systems fell toPakistans share. East Bengal, now Bangladesh, which comprisesthe fertile Ganga Brahmaputra delta region also went to Pakistan.

The irrigation works which remained with India barring some of theold works in Uttar Pradesh and in the deltas of the South, weremostly of a protective nature, and meant more to ward off faminethan to produce significant yields.

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ie. modern well designed large scale irrigation systemswere developed mainly after the 18thcentury. Irrigationtechnology made rapid strides in the 20th century.

After independence, a massive effort was launched byGovernment of India to develop several dam reservoirsand canal networks. The importance attached toirrigation projects in Independent India can be gauged

by the fact that while inaugurating and dedicating theBhakra dam Pt. Nehru called it as "new temple ofresurgent India"

Cl ifi ti f il t

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Classification of soil waterGravitational water

Capillary waterHygroscopic water

1. Gravitational water: A soil sample

saturated with water and left to drain theexcess out by gravity holds on to a certainamount of water. The volume of water thatcould easily drain off is termed as the

gravitational water. This water is notavailable for plants use as it drains offrapidly from the root zone.

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2.Capillary water: the water contentretained in the soil after the gravitational

water has drained off from the soil is knownas the capillary water. This water is held inthe soil by surface tension. Plant rootsgradually absorb the capillary water andthus constitute the principle source of waterfor plant growth

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3.Hygroscopic water: the water that anoven dry sample of soil absorbs when

exposed to moist air is termed ashygroscopic water. It is held as a very thinfilm over the surface of the soil particles andis under tremendous negative (gauge)pressure. This water is not available toplants.

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Crop water requirement

It is essential to know the water

requirement of a crop which is the total

quantity of water required from its sowing

time up to harvest. Naturally differentcrops may have different water

requirements at different places of the

same country, depending upon theclimate, type of soil, method of cultivation,effective rain etc.

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crop periodbase period

The total water required for crop growth is

not uniformly distributed over its entire life

span which is also called crop period.

Actually, the watering stops same time

before harvest and the time duration from

the first irrigation during sowing up to the

last before harvest is called base period.

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DELTA

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DELTA

The total depth of water required to raise a

crop over a unit area of land is usually

called delta

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Rice

1000mm to 1500mm for heavy soils

1500mm to 2000mm for medium soils

2000 to 2500 for light soils or deep water table

1600mm for upland conditions

Wheat

250mm to 400mm in northern India

500mm to 600mm in Central India

Barley: 450mm

Maize

100mm during rainy season

500mm during winter season

900mm during summer season

Cotton: 400 500mm

Sugarcane

1400mm to 1500mm in Bihar 1600mm to 1700mm in Andhra Pradesh

1700mm to 1800mm in Punjab

2200mm to 2400mm in Madhya Pradesh

2800mm to 3000mm in Maharashtra

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Duty of water

The term dutymeans the area of land thatcan be irrigated with unit volume ofirrigation water.

Quantitatively, duty is defined as the areaof land expressed in hectares that can beirrigated with unit discharge, that is,1 cumec flowing throughout the baseperiod, expressed in days.

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Imagine a field growing a single crop

having a base period B days and a Delta

mm which is being supplied by a source

located at the head (uppermost point) ofthe field, as shown in Figures 2 and 3.

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The water being supplied may be through the diversion of

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The water being supplied may be through the diversion of

river water through a canal, or it could be using groundwater by pumping (Figure 4).

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If the water supplied is just enough to raise

the crop within D hectares of the field, then

a relationship may be found out amongst

all the variables as: Volume of water supplied = B*60*60*24 m3

Area of crop irrigated = D*104 m2

= 8.64 B metersd

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Factor affecting duty of water

Choice of the crop

Choice of the Variety

Conveyance efficiency of the irrigation system

Types of the Channel

Types of the regulating devices. Total area to be irrigated. Total volume of water available

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Type of crop: As different crops requiredifferent amount of water for maturity,

duties are also required. The duty would

vary inversely as the water requirement of

crop.

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Climate season and type of soil: Some

water applied to the field is expected to belost through evaporation and deep

percolation. Evaporation loss has a direct bearing on the

prevalent climate and percolation may beduring drier seasons when the water table is

low and soil is also dry. Percolation losswould be more for sandy soils than silty orclayey soils.

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Efficiency of cultivation methods: If the tillage

and methods of water application are faulty andless efficient, then the amount of water actuallyreaching the plant roots would be less. Hence, forproper crop growth more water would be requiredthan an equivalent efficient system. Also, if thewater is conveyed over long distances through

field channels before being finally applied to thefield, then also the duty will rise due to the lossestaking place in the channels.

CROP SEASONS KHARIF AND

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CROP SEASONS - KHARIF AND

RABI

Traditionally, there are three cropping seasons -rabi, kharif and zaid.

Rabi cropping season extends from October-

November to March-April, Kharif from June-July to September-October.

Zaid season spans during interregnum period

between rabi and kharif.

Major rabi crops are wheat gram, pea and

Major kharif crops are paddy and jowar.

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crop seasons and important crops

Season PeriodFrom-To

BasePeriod in

Days

Common Crops

Kharif 15th June-14"

Oct

123 Rice, Jowar, Cotton,, etc.

Rabbi 15" 0ct- 14"

Feb

122 Wheat, Gram, Linseed, etc

Hot weather 5" Feb-14" Jun 120 Only irrigated crops like

vegetables

EightMonthly 15"June- 14"Feb

245 obacco, Cotton, Groundnut, etc

Annual 1 5th June-14"

June

365 Sugarcane, Orchards, et

Frequency of Irrigation

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Frequency of Irrigation

Design Frequency The design frequency is equal to

(Net irrigation requirement in the effective crop root zone -

Moisture content of the same zone at the time of starting of irrigation)

Peak period moistures rate of crop

Amount of Water to Apply per IrrigationWith 'full irrigation' the amount of water required per irrigation is

computed as follows :

I =Dr (fcfm)

Irrigation efficiency

in which,

I=

Amount of water to be applied, cm, Dr = Depth of root zone, cm,

fc= Soil moisture content at field capacity, and

fm= Soil moisture content prior to irrigation.

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Command Area"The area which lies on down stream side of project to which water can reachby gravity action." There are the three types of commanded areas.

Gross Commanded Area (G.C.A)

The Gross commanded area is the total area lying between drainageboundaries which can be irrigated by a canal system.

This is defined as total area that can be irrigated by a canal system onthe perception that unlimited quantity of water is available. It is the totalarea that may theoretically be served by the irrigation system. But thismay include inhibited areas, roads, ponds, uncultivable areas etc whichwould not be irrigated.

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Cultivable Commanded Area (C.C.A)It is the net area, which can be irrigated by a canalsystem. It includes all land on which cultivation ispossible, though all area may not be under

cultivation at the time.

G.C.A. = C.C.A. + Uncultivable areaIrrigable Commanded Area (1.C.A)

It is the part of cultivable commanded area, whichcan be irrigated. All the C.C.A. cannot be irrigatedbecause of high elevation.

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Intensity of Irrigation It is the ratio of area irrigated per season to total

irrigable areas or small projects is based on this.

is defined as the percentage of the irrigation proposed tobe irrigated annually. Usually the areas irrigated duringeach crop season (Rabi, Kharif, etc) is expressed as apercentage of the CCA which represents the intensity of

irrigation for the crop season. By adding the intensities ofirrigation for all crop seasons the yearly intensity ofirrigation to be obtained

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Consumptive use

Cu use for a particular crop is defined as the

amount of water used by the plant in

transpiration( building of plant tissues etc) and

evaporation from the adjacent soils or plants,in any specified time.

Values of monthly Cu over the entire cropperiod are then used to determine the

irrigation requirement of the crop

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Effective rainfall (Re)

Re is defined as the precipitation falling

during the growing period of a crop that is

available to meet the evapo-transpiration

needs of crop.

It doesn't include the precipitation lost

through the deep percolation brloe the root

zone or the water lost as surface runoff

Consumptive irrigation requirement

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Consumptive irrigation requirement

(CIR)

It is the amount of the irrigation water

required to meet the evapo-transpiration

needs of the crop during its full growth

It is exclusive of effective rainfall , stored soil

moisture or ground water

Then CIR= Cu-Re

Net Irrigation requirement

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Net Irrigation requirement

(NIR)

NIR= Cu-Re + Water lost as percolation in

satisfying needs such as leaching etc.

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