PRACTICAL MANUAL ON WATER - ISCA

PRACTICAL MANUAL ON WATER

MANAGEMENT

Dr.S.Krishnaprabu Assistant professor,

Department of Agronomy,

Annamalai University, Tamil Nadu

2019

Ideal International E – PublicationPvt. Ltd. www.isca.co.in

427, Palhar Nagar, RAPTC, VIP-Road, Indore-452005 (MP) INDIA

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E-mail: [email protected], Website:www.isca.co.in

Title: PRACTICAL MANUAL ON WATER

MANAGEMENT

Author(s): Dr. S. Krishnaprabu

Edition: First

Volume: I

© Copyright Reserved

2019

All rights reserved. No part of this publication may be reproduced,

stored, in a retrieval system or transmitted, in any form or by any means,

electronic, mechanical, photocopying, reordering or otherwise, without

the prior permission of the publisher.

ISBN: 978-93-86675-97-2

PRACTICAL MANUAL ON WATER MANAGEMENT 1

Ideal International E- Publication

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ExNo: 1

DETERMINATION OF SOIL MOISTURE CONTENT BY

DIFFERENT METHODS

Soil moisture measurements are important in suitable scheduling of

irrigations& estimating the amount of water to be applied for each irrigation.

The principal method of expressing soil moisture are:-

i)Moisture present in the given soil.

ii) The stress or tension under which the water is held by the soil

The relationship between these two properties throughout the entire

moisture range gives a good deal of insight into the physical properties of a

soil.

Expressing the amount of soil moisture:

Soil Moisture on weight basis is based on the dry weight of the sample.

Soil Moisture percent by weight =

( ) ( )

( )

Moisture percent by volume =Moisture content Percent by weight Bulkdensity

Gravimetric method of Soil moisture measurement

The basic measurement of soil moisture are made on soil samples of a

known weight on volume. Soil samples are collected with a soil auger or

sampling tube. Thesamples are taken from the desired-depths at several

locations. They are collected in air tight aluminum containers. The soil samples

arc weighed & they are dried in an oven at 105°C for about 24hrs, until all the

entire moisture is dried off and also to have a constant weight of a sample.



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Then the dried sample is weighed again. The difference in weight is the amount

of moisture present in the soil sample.

Soil Moisture =

( )

Where,

W1 - Initial weight of soil sample (g)

W2 - Oven dried weight of soil sample (g)

It is expressed in percentage

Tensiometer:

It provides a direct measure of the tension with which water is held by

the soil. They measure the matric or capillary potential. It can also be used to

estimate the soil moisture content.

The tensiometer consists of a porous ceramic cup, filled with water

which is buried in the soil at any desired depth & connected to a water filled

tube to a monometer or vaccumguage. The scales are generally calibrated in

either hundred of an atmosphere or in centimeters of water. When the

tensiometer is placed in the soil where the tension measurement is to be made,

the bulk water in the porous cup comesinto hydraulic contact & tends to

equilibrate with soil moisture through the pores inthe ceramic cup. When

initially placed in the soil, water contained in the tensiometeris generally at

atmospheric pressure, exercise which draws out a certain amount of water from

the rigid & air tight tensiometer thus causing a drop in its hydrostatic pressure.

The pressure is indicated by the manometer or vacuum gauge. Increase insoil

water content reduces tension & lowers the reading.

Tension measurements by tensiometers are generally limited to matric

suction values of below 1 atm.

Ex. No. 2ESTIMATION OF SOIL MOISTURE BY ELECTRICAL



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RESISTANCE BLOCKS ANDNEUTRON MOISTURE METER

Gypsum blocks

The dependence of electrical conductivity of porous soild on the amount

of water forms the basis of this method. Porous block containing electrode

when embedded in soil, the moisture content of the porous body comes in

equilibrium with soil moisture. The electrical resistance between the two

electrodes varies with moisture of porous block which is in equilibrium with

soil moisture. The resistance is measured by a resistance meter. In wet soil the

resistance is low and in dry soil is high, with proper calibrations the moisture

from FC to WP can be readily determined.

The resistance blocks are made of various materials like Gypsum, nylon,

fibre glass, plaster of paris or combination of these materials. The blocks are

generally rectangular shaped. A consentient size of a gypsum block is 5.5cm

long, 3.75cm wide & 2cm thick. The most commonly used electrical resistance

instrument was developed by Bouyoucos (1949). Hence they are also called as

"Bouyoucos Moisture meter".

Limitations

In saline Soils danger of cracking of the block is possible due to high

shrinking nature and so each gypsum block has to be calibrated separately.

Neutron moisture meter

The neutron scattering method is a rapid means of making insitu

measurementof soil moisture.



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Principle

Measurement of the number of hydrogen nuclei, that are present in a

unit volume of soil, their number being direct function of the number of water

molecules contained in the same volume. This measurement is made by

inserting a source of fast neutrons & counting the slow neutrons produced. The

Neutron moisture meter consists of two principal parts.

1)A probe

2)A scale / rate meter

Probe

Lowered in acess tube inserted vertically in the soil & which contains a source

of fast neutrons & a detector.

Scale or rate meter

It is usually battery operated & portable to monitor the flux of slow

neutrons which is proportion to the soil water content.

In use, the probe is lowered into the access tube & counting rates are

determined at the desire depths. The count rate adjusted for the background &

standardized to counts made in a tank of pure water, are then calibrated against

volumetric determination of soil moisture content. It sources as a standard

absorbersfor checking the readings potential shield the equipments can be used

safely withreasonable care & attention to safety rules.



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Depth (cm) W1 W2 Moisture

content(%)

0-15 225 196 14.79

15-30 206 177.5 16.0

30-45 198 164.5 20.36

Principle

When the probe is placed inside the soil at desired depth, fast moving

neutrons are released by the source and it colloids with hydrogen nuclei of

water, returns slowly to the detector tube and be captured. As a result transient

break down of gas in tube and the production of short period pulse is measured.



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Ex No: 3DETERMINATION OF SOIL MOISTURE CONSTANTS

Soil moisture constant is nothing but the status of soil mass or changes

occurring in the soil mass after the irrigation (or) rainfall. In real sense we

cannot expect constants of soil moisture, since it is very dynamic & always

tend to change due to potential gradient or pressure gradient. These

phenomenon helps to find out the soil moisture status, the availability condition

of soil moisture, time & quantity of irrigation water to be applied etc.,

The soil moisture constant are

1. Saturation point or maximum water holding capacity (WHC)

2. Field capacity (FC)

3. Permenant wilting point (PWP)

4. Available soil moisture(ASM)

Saturation point or maximum water holding capacity: (WHC)

Immediately after surface irrigation or heavy down pour (or) good

amount of rainfall, subsurface pores are completely filled up with water. At this

stage all the micro & macro pores are filled with water. This condition is said

to be saturation point of soil. In saturation point, the water is held without any

force or tension or the tension is almost zero. At this point the gravitation force

tends to pull some water or part of water which move downwards due to

gravitational force. This water is known as gravitational water or free water.

Field capacity (FC)

This can be defined as the moisture content present in the soil surface

after the drainage of water due to gravitation force is stopped (or)ceased or

become very slow.Hence it can also be stated as the moisture content retained



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against the gravitational force. It can also be defined as the moisture present in

the microscopic or capillary pore which cannot be drained off due to gravity.

Normally it ranges from 1710th

atmosphere to 173rd

atmosphere for

coarse & fine textured soil. The field capacity is the upper limit of available

water to plants or maximum water available point to the plants. The field

capacity of soil is influenced by the soil texture or size of the soil particles,

structure, & amount of water applied.

After irrigation or rainfall, soil will reach its field capacity in two or

three daysdepending upon the soil texture. This time period to reach the field

capacity conditionis increased, if soils are fine textured & rich in organic

matter, which restricts thedownward movement of water.

Permanent wilting point (PWP)

It is the condition of soil moisture at which plant cannot extract water

from soil due to its high tension, the soil moisture condition at which water is

held so tight to the soil particles & this water cannot be removed by the plant

roots.

The plant cannot regain its turgidity even the water is made available to

the plants. This condition is called permanent wilting point. At this point soil

moisture tension will reach very high i.e. the moisture level held in the soil

particles with a tension of about 14 to 15 atmosphere. Wilting & dropping of

leaves are most common symptoms of PWP. Drought resistant crops will show

the symptoms like stunted plant growth, droping of leaves, change in leaf

colour, droping of flowers, fruits etc.



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Available soil moisture (ASM)

This is the moisture content between the FC & the PWP level. After

reaching PWP, the plant roots cannot extract water.

ASM can be defined as the water available in the capillary pores after

the cessation of gravitational water &upto the limit of permanent wilting point.

ASM =

ASM - Available soil moisture in root zone.

FC - Field capacity

PWP - Permanent wilting point

BD - Bulk density of soil g/cc

D - Depth of root zone in cm.

AWC = ∑( )

i =ith

layer

di = denotes depth of ith

layer

bdi = bulk density of ith

layer

n = number of layer



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Ex. No.4 MEASUREMENT OF IRRIGATION WATER

Measurement of waterinmotion,i.eflowinginrivers,canals,etc is

expressed in rate of flow units such as litres/second, 1hr/ hacm/s.

1m3 =1000L

i) Rectangular weir:

The discharge rate is calculated by the formula Q = 0.0184 LH3/2

(Suppressed rectangular weir). Where

Q = Discharge in litres / second

L = Length of the crest in cm crest-the bottom of weirnotch

H = The depth of water flowering over the weir crest in cm

ii) Trapezodial weir (or) Cipollete weir

Q = 0.0186LH3/2

iii) Triangular or v notch weir

Q = 0.0138 H5/2

a. Orifice

An orifice is a circular or rectangular opening provided in the structure.

Q = 0.61 x 10-3

A √ ,where

A = area of orifice in cm2

g = Acceleration due to gravity 1 sec2(980cm/sec

2)

H =Head causing flow in cm.



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b. Parshall flumes:

It is an open channel type measuring device. Sand or silt in the flowing

water does not affected its accuracy and velocity of the upstream has very little

influence. Itconsists of converging section at its upstream, a diverging section

at down stream. Two measuring walls, one by the side of the upstream at a

distance 2/3cm of converging length from the throat and the other by the side

of the downstream throat section are provided to determinate of discharge.

Stilling wells can be used in flumes if turbulence is present. When the flow is

smooth a plastic scale fixed to inside the flume, will be sufficient to measure

the lead. Parshall flumes of 3, 5, 15, 23 and 30 corn sizes are generally used in

filled measurements size is determined by its width of the throat.

Dilution method

Large quantity of chemical dye (tracer) is dissolved in running water

stream and its disappearance is evaluated. Nacl, sodium dichromate can be

used.



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Ex No:5 CALCULATION OF IRRIGATION WATER

Water is measured under two conditions at rest and in motion. Water at

rest reservoirs eg: ponds are measured in units of volume such as litre, -cubic

meter, hectare centimeter and measurement of water in motion ie flowing in

nivers, canals etc. is expressed in rate of flow units such as litres / second 1hr

hacm /s. 1m3 = 1000L

Hectare - Centimeter

A volume of water necessary to cover an area of I ha to a depth of 1m

i.e. 100 m3 = 100 1000 - 100000 litres.

Hectare - meter

A volume of water necessary to cover an area of 1 ha to a depth of 1m

i.e. 10000m3 = 10000 1000 = 10 million lakes.

Litre per second

A continuous flow amounting litre passing through a point each second.

Cubic meter per second

A flow of water equivalent to a stream 1m wide and 1 metre depth

flowing at a velocity of 1 meter per second.

There are four ways by which water can be measured,

1.Volumetric measurement

2.Velocity area method

3.Measuring structures

4.Tracer methods



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Volumetric method of water measurement

A simple way of measuring small irrigation streams or pumps is to

collect the flow in a container of known volume for a measured period of time.

For this, an ordinary bucket or board or cement truff is used as a container. The

time required to fill the container is noted. The rate of flow is measured by the

formula

Discharge rate (1/s) = ( )

( )

Q velocity = Area method

The rate of flow passing through a point in a open channel is determined

by multiplying the cross sectional areas of the flow channel by the average

velocity of water.

Q = a v

Where Q = discharge rate m /s

a = area of cross section of channel ism2 and

V = Velocity of flow (seconds)

The cross sectional area is determined by direct measurement velocity is

measured by.

a)Float method

This method is a rough estimation of flow in a channel. A long necked

bottle partly filled with water or a block of wood is used a float. Select a

straight 30m long fairly uniform, cross section channel. Measure the depth and

width in five different places with in trial section andarrive average cross

sectional area. A string is stretched across sectional area at each end of the

section at right angles to the direction of flow. The float is placed in the up



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stream at a short distance a head from the storming point. Note the initial and

final times when it croses the standing point and end point in the down stream.

The time taken by the float travel in 30 m iscalculated. Repeat this trace for

five times to arrive a average time of travel. Since the velocity of the float on

the surface of water will be greater than the average velocity of the stream, It is

necessary to correct the measurement by a constant factor of 0.85.

b.Current meter

Velocity of a water in a stream is directly measured by current meter. It

is a small instrument containing a revolving wheel or vane by the movement of

water.

The wheel is suspended by a cable for measurement in deep streams or

attached to a rod in shallow streams. The number of revolutions of the wheel in

a given time is noted and the corresponding velocity is recorded from a

calibration table.

c.Water meters

Water meters are available in different size to record the velocity of

water flows in a pipe. It consists of multi blade propeller made up of metal,

plastic or rubber, rotating in a vertical plane and geared to a totalizer in such a

manner that a numerical counter can totalize the flow in any desired volumetric

units.



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Ex No: 6 SURFACE METHODS OF IRRIGATION

It is the way of which water is applied effectively to the cropped field

without much application loss and to facilitate better environment for crop

growth.

The factors like soil texture, structure, porosity, infiltration rate, soil

depth, topography of land, rainfall, humidity, temperature wind velocity,

radiation, quantity and quality of water available, the flow velocity, nature and

value of crop, and spacing adopted influence the method of irrigation.

There are four methods of irrigation i.e surface, sub-surface, sprinkler or

overhead and trickle irrigation

A. Surface or Gravity irrigation:

It is the common method of irrigation practiced all over the world. In

this method water is applied directly to the surface by providing some checks

to the water flow.

1.Flooding

This method is exclusively suitable for lowland rice Water from the

channel is allowed into the field. Spreading of water is due to presence of water

in Rice field. This method needs enormous quantity of water and less labour

and have a very low water use efficiency by the crop.

2.Check basin method

It is the most common method among the surface method of irrigation

and it is suitable for crops like groundnut, ragi, cumbu, wheat, water grass etc.

In this method, Ac field is graded by bunds on all the four sides. The plot size

depends on soil texture and stream size of the channel. Water from the main

channel supplies water to thelateral channel which in turn supplies water to two

rows of check basin one afteranother.



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Advantages

Water can be applied uniformly and even with small streams.

Disadvantages

More land in wasted by forming bunds and channels. It requires more

labourers for forming basins and irrigations. Inter cultivation by implements is

difficult.

3) Ring basin method:

This method is suitable for coconut orchards etc. This method is similar

to check basin. In check basin, entire field is irrigated where as in the basin

method, againaround the trees are irrigated. The basins are rounded or square in

shape. Basins areconnected by irrigation channel which are connected to lateral

channels.



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Ex No. 7BORDER STRIP AND FURROW METHOD OF IRRIGATION

1.Border strip method:

This method is suitable for medium to heavy soil and for close growing crops

like cumbu, ragiIt is not recommended for light textured soils. In this method,

the field is laid out into long narrow strips, bordered with small bunds. End of

the strip may be closed, the borders are laid out along the general slopes of less

than 0.5 percent. The narrow strip facilitates the uniform flow of water.

2.Ridges and furrow irrigation:

This method is suitable to wide spaced row planted crops like sugarcane, cotton

tobacco, potato and vegetablecrops. Water is applied to the field in furrows

between the two ridges and the top of ridge is not directly wetted. The size

depends on soil type. Size & shape of furrows depend on crops grown and

spacing adopted for the crop.

3.Corrugation

This method is adopted for close growing crops, mostly rainfed of small

grain crops Typical corrugation has a channel of 10cm deep of 40-75cm apart.

Application of water through shallow furrow is known as corrugated furrow

irrigation.

4.Cablegation:

It is an automated method of surface irrigation and labour can be saved

compared to other surface method.

This system has a pipe and two outlets are positioned near the top side

of pipe are always open. The spacing between the gates corresponds to row

spacing at a t of oil. The pipe is laid on a precise grade along the top edge of

field. Water isalways allowed upto the top edge of field. Water is always

allowed upto half its height into pipe. Inside the pipe a movable plug is



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provided and its allowed to move down slope at a controlled rate. The upstream

end of the play is attached to a case on reel. The rate at which plug moves and

at which irrigation progress across the field. The water pressure provides force

to move plug. i.e. The rate of movement of plug is controlled to suit water

requirement of each furrow. Water always flows in the pipe below in level to

outlets excepts near plug. The obstruction caused by plug increases the height

of water in pipe and water comes out through the outlets. The outlets farther

from plug deliver at lower rates. Hence this system is fully automated it is a

comparatively a more efficient method in surface irrigation than any other

method.



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Ex No. 8 SPRINKLER AND DRIP IRRIGATION

Sprinkler / over head irrigation

Application of water in the form of spray or rain drops over the crop is

termed as sprinkler irrigation

i) Thismethod is suitable for all the crops except rice. Most commonly

adopted for plantation crops, cash crops and in orchards,

ii) Suitable to areas where water and labour are scarce

iii) Suitable for coarse textured soil

iv) Suitable to areas where soil erosion and surface run off are common,

v) Suitable to shallow soils where levelling operation is not possible.

Sprinkler system consists a pumping unit of mainline, sub-mains, lateral

and sprinklers. Centrifugal pump is used, when the distance from the pump

inlet to the water surface is less than 8m. The driving unit may be an electric

motor or an internal combustion engine. Water is conveyed under pressure,

from the water source by a pump, through a network of portable light weight-

quick coupling pipelines called main, sub-mains and laterals and sprayed on the

field through sprinklers mounted at regular intervals. Mainline conveys water

from the source and to it sub mains, the sub mains conveys -water to the lateral

which inturn supply water to the sprinklers. There are two types of sprinklers

are available namely rotating and field type.

Rotating head can be adopted for a wide range of application rates and

spacing. It consists small metal ring (Vane) with a spring. The water projected

through nozzle strike the metal ring which changes its direction by the help of

the spring attached to their which turn causes spray of water in all directions.

The sprinkler head is attachedto lateral pipes with the help of raiser pipe. The

higher of raiser pipe depends on the height of crop.



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In fixed head sprinklers the nozzle is stationary, spray water in one

direction and commonly used to irrigate small lawns, nurseries, orchards. Out

of total discharge from sprinkler. 2 to 8% may be lost by evaporation sprinkler

can discharge more than 1000 litres. In 1 hour and the throw distance is more

than 10m.

Mini / micro sprinklers are suitable for forest trees. Delivers 28 to 223

It/hr and the throw distance 0.9 to 4.0 in.

Types of sprinkler

a.Portable: The entire system can be moved from field.

b.Semi portable: Has portable pipe lines and pumping unit to field is

stationary.

c.Semi permanent: Has portable laterals, permanent main pipe line, and

stationary pumping unit.

Advantages:

1. The water loss is very minimum is no conveyance loss and hence it is

possible to increase the irrigatable area. Water saving efficiency is 25-

50% when compared to surface irrigation.

2. Land leveling is not necessary

3. It regulates the microclimate of the crop during freezing temperatures

4. Absence of surface run-off, since application rate is less than the intake

of soil.

5. Water can be applied at any controlled rate with uniform distribution

and with high water use efficiency.

6. Enhance the growth of the plant

7. Increase the yield of plantation crops and suitable for high altitude crops

like tea, coffee, cardomametc

8. Improves the quality of products.



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Disadvantages

1. It needs high initial investments

2. Not suitable to use for clayey soil

3. It needs electrical power

4. Wind drift may carry the water away from target plant

5. In the field square shaped corners are neglected since spray pattern in

circular.

6. Technical personal is needed for operation and maintenance

7. Mechanical difficulties are expected.

Drip / Trickle irrigation

Application of water drop to the root zone of crop. Drip system was

invented byengineer named. Blase in 1940 and he patened this in 1964.

This method is suitable for

i) Light (Sandy) soil / poorsoil

ii) Areas where water is deficit / Low annual rainfall

iii) Areas where discharge from the well is not available low lying areas

iv) In areas of water with high PH

v) Holds good for wide spaced crops like sugarcane cotton, maize,

Tobacco, potato, Chillies, coconut, plantation crops and in orchards

etc.

vi) Dry regions



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Drip system consists of a pump to lift water from the source. After lifting

thiswater it is stored head tank of 3m in size resting on a raised platform about

4 to 5m to maintain pressure. Central distribution system consists of value

water meters, fertilizer unit (fertilizer injected into the system) Filtration

system of prevent the clogging emmitters with salt clay silt microorganisms,

suspended organic and in organic otters. Mesh and sand filter are two types of

filters used.

Main pipe line is made up of PVC with a diameter of between 2.5 to

7.5cm andare available at a pressure rating of 2.5, 4.0, 6.0 and 10kg/cm2. The

main line designdepends on the topography, operating pressure, layout of

laterals, sub mains from eachflatlet along main line. Sub mains are attached to

main pipe line and distributes waterto laterals and its diameter is between 2.5 to

5.0 cm. Laterals are provided for eachrowof the crop and it size may be 0.9, 1.2

or 1.5 cm. The drippers uniformity shouldbe compact, inexpensive not vary

significantly with pressure. Large cross section areaold clogging relatively of

low discharge (2 to 4m). Emitters are of two types, point source system

discharge water from individual multiple outlets are space 1m apart.

Advantages

1. Seepage, percolation and evaporation loses are reduced.

2. Water use efficiency can be increased upto 40 percent

3. Suitable to all field types of wide space crops.

4. Suitable to all topography

5. Facilities easy infiltration due to the slow rate water of application

6. The root zone is always maintained to the field capacity.

7. Weed growth is restricted due to limited area of wetting.



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Ex. No. 9 ESTIMATION OF CROP WATER REQUIREMENT BY

VARIOUSMETHODS

Crop water requirement may be defined as scientific management

technique of a allocating irrigation water based on the individual crop water

requirement under different soil and climatic condition, with an aim to achieve

maximum crop production per unit of water applied over a unit area in unit

time.

Approach in Crop water requirement

There are several approaches for

i. Soil moisture regime approach

ii. Climatologic approach

iii. Remote sensing

i. Soil moisture regine approaches

These approaches involve determination of water content of the soil and

finding deficit in available moisture at which it is proposed to irrigate. When

the soil moisture reaches a pre fixed value, may be 40% of available soil

moisture degree of -ment can be estimated by gravimetric method, or by using

Neutron moisture :Tensiometer, Resistance blocks etc, and we can schedule

irrigation.

Gravimetric methods

This is a direct and reliable method, where samples are collected, weighed and

dried at 105-110°C for about 24 hrs until constant weight is obtained and

reweighted after drying the moisture lost is expressed as a percentage over dry

weight of the soil.



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Neutron moisture meter

The neutron probe has been used extensively in research situations to

determine soil moisture. A neutron probe or neutron moisture gauge contains a

radioactive source that sends out fast neutrons. There fast neutrons are about

with inthe probe measures the rates. However, every soil has some background

hydrogen. Sources that are not related to water, Calibration is important for

each soil. To measure soil moisture with a neutron probe is lowered to the

desired depth.

Tensiometer:

Tensiometers are instruments that are used to measure the soil water

tesion Basic principles of this method is that the capillary tension increased

with decrease in moisture content. Tensiometers or irrometers consist of a

porous cup made of ceramic material it is manometer. At the opening at the top

and tightly corked the porous up is buried to the material of the cup between

moisture depletes, water moves to the soil creating a vacuum in the tube which

units are converted into soil moisture percentage tensiometer works well with

in tensiometer works well within a narrow moisture range up to 0.8 bar. At low

moisture content tension increase and air may enter the system through the cup

affecting perfect functioning of the instrument.

Electrical Resistance methods:

It works on the principle based on the relationship between the

electricalresistance and moisture content of the soil electrical & resistance.

Increases with decrease in moisture content the stone blocks are most

widely used. Electrodes embedded depth in the block. This method is not

suitable for soils at having high salinity as resistance increase in salinity.



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II. Climatulogicalapproach:

The basic principles employed with this approach is estimation of daily

potential evapo - transpiration rates. Based on the ET, Irrigation in scheduled.

Remote sensing

When a single crop in grown in large area, irrigation scheduling can be

done with the help of remote sensing data. Reflectance of solar radiation by the

plants with sufficient amount of water is different from that of stressed plant.

With help of IR thermometer we can study the difference in thermal

temperature between normal and a stressed plant. The readings are compared

and calibrated.

Sensitive stages of different crops (Cereals & Millets)

Crops Critical stages / Sensitive stages

Rice Panicle initiation, heading & flowering

Sorghum Flowering & grain formation

Maize Prior to tasseling and grain filling

Cumbu Heading &flowering

Ragi Primordial initiation & flowering

Wheat Crown root initation, tillering& booting



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Oil seeds

Groundnut Flowering, peg initiation, penetration to the soil &

pod development

Sesame Blooming to maturity

Sunflower Two to weeks before &after flowering

Soybean Blooming & seed formation

Sunflower From rosette to flowering

Castor Full growing period

Cash crop

Cotton Flowering & Boll formation

Sugarcane Maximum vegetative stage

Tobacco Immediately after transplanting

Legumes:

Alfa-alfa Immediately after cutting for hay crops flowering for

seed crops

Peas & Beans Flowering & pod formation

Coconut Nursery stage & root enlargement

Potato Tuber initiation & maturity

Banana Throughout the growth

Citrus Flowering, fruit setting & enlargement

Mango Flowering

Coffee Flowering & fruit development



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Ex No. 10 IRRIGATION SCHEDULING

Irrigation scheduling is defined as frequency with which water is to be

applied based on needs of the crop & Nature of the soil.

Irrigation scheduling may be defined as scientific management

technique of allocating irrigation water based on the individual crop water

requirement under different soil and climatic conditions, with an aim to achieve

maximum crop production per unit of water applied over a unit area in unit

time.

where, IW = Depth of water to be applied.

CPE = Cumulative pan evaporation for a particular period

Theoretical approach of irrigation schedule:

1.Direct approach:

a) Depth interval & yield approach

b) Soil Moisture deficit & optimum moisture regime approach

c) Sensitive crop approach

d) Plant observation method

2.Indirect or predictive approach:

a. Critical stage or phenological stage approach

b. Meteorological or climatological approach

3.Mathematical approach

a. Estimation method approach

b. Simple calculation method

c. Simulation approach - Computing & modeling

d. Empirical approach



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4. System as a whole approach

a. Rotational water supply schedule

1. Direct approach

A. Depth interval & yield approach

In this method different depths of irrigation water at different time

intervals are tried without considering the soil & weather parameters.

The irrigation treatment which gives the maximum yield with minimum

depth & extended interval is chosen as the best irrigation schedule.

Disadvantages

Rainfall is not taken into account

Ground water contribution is not taken into account

Soil parameters are not taken for calculating irrigation requirement

&hence this approach has the lowest advantage.

B. Soil Moisture deficit &optimum moisture regime approach

This approach considers soil moisture content in the root zone of the

crop for fixing the schedule. The degree of depletion is measured through

percentage of available moisture by using gravimetric tensiometer, resistance

block, Neutron-Probe etc.,

Disadvantages

Soil moisture alone is taken into account

It cannot be taken for all type of soil in particular region.



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C.Scientific crop approach

The crop which are grown for the fresh leaves or fruits are more

sensitive to water shortage than the which are grow for their dry seeds or fruits.

On this sensitivity the crops can be indered as low, low to medium, medium to

high and high.

D.Plant observation method

Visual signs of dropping, curling, rolling of leaves, wilting of plants are

the common indicators. Growth indicators such as cell elongation rate, plant

water content, leaf water potential are used for scheduling irrigation.

Disadvantage

No accuracy in finding the crop water & need.

Sometimes sensitive symptoms are evident only after reaching almost.

The witting point. So, yield loss will occur.

i) Indicator plant technique

To know the stress symptoms earlier sensitive crops are planted in

random in the field & based on the tre symptoms noticed in such plants,

scheduling of irrigation can be made. This technique is called indicator plant

technique.

ii) Micro plot tech or indicator plot technique

The field soil is mixed with sand in 1:2 ratio& filled in the microplot

made in the field. The seed of the same crop & Variety is grown in microplots

with all similar cultural practices as that of the main crop. The crops in micro

plots show early stress symptoms than that of main field, because of more ratio

of sand.



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2. Indirect approach

A.Critical stage or phonological stage approach

The growth period of annual crop can be divided into four growth

stages.

a. Initial stage

b. Crop development stage

c. Mid season stage

d. Late season stage .

The stage at which the water stress cause severe yield reduction is

known as critical stage of water requirement It is also known as moisture

sensitive period.

B.Metrological approach

The basic principle employed with this is estimation of daily potential

evapo transpiration rates.

Short term evapotranspiration ratio at various stage of plant development.

a. Soil water retention characteristics

b. Permeable soil water deficit in respect to evaporative demand.

c. Effective rooting depth of the crop grown.

Irrigation scheduling is based an irrigation depth & cumulative pan

evaporation. The irrigation for different crops are fixed based on the soil &

climate conditions. The rate of IW/CPE which gives relatively best yield is

fixed for each crop by doing experiment with different ratios.



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Advantages:

Gives best correlation compared to other formulae where climatic

parameters are considered.

Disadvantages:

This approach is subjected to marked influence by the selecting pan site.

4. System as a whole approach

A traditional water supply is one of the techniques in irrigation

waterdistribution management. It aims at equal distribution of irrigation water

irrespective of location of the land in the command area by enforcing irrigation

line schedules.

According to the availability of irrigation water, stabilized field channels

& group wise irrigation requirement, time schedules are evolved. The irrigation

will be done strictly in accordance with the group-wise time schedules by the

block committees. Within the group, the time is to be shared by the formers

within the group by themselves.



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Ex. No.11 CALCULATION OF IRRIGATION EFFICIENCY

PARAMETERS

Irrigation efficiency indicates how efficiently the available water

supplied is

being used by the plant.

It depends upon design of irrigation system, degree of plant protection,

skill &care of irrigator, are the principles factor influencing efficiency of

irrigation

Loss of irrigation water occurred in conveyance & distribution system,

Non uniform distribution of water over the field, percolation below crop

root zone & with sprinklers irrigation evaporation from the spray &

retention of water on foliage, incase of large field loss may occur due to

lay runoff & end of irrigation borders & furrows.

The losses can be held to a minimum by adequate planning of irrigations

system, proper design of irrigation method adequate land preparation, &

efficient operation of system.

1. Water conveyance efficiency (WCE):

Used to measure the efficiency of water conveyance system associated

with canal network, water forces at the field channels, it is also applicable

water conveyedin channels from well.

EC=

EC= Water convenience efficiency percentage

Wf = water delivered to the irrigated plot (at the field supply channel).

Wd = water delivered from the source.



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2. Water application efficiency

WAE=

EA - Water application efficiency in percentage

Ws - Water stored in root zone of plants

Wf- Water delivered to the field at the field supply channel.

Water application efficiency below 100% are due to seepage losses from

field distribution channels &depercolation below the crop root zone. In general

water application efficiency decreases as the amount of water applied during

each irrigation is increases.

3. Water storage efficiency

The concept of water storage efficiency is useful in evaluating the water

storage efficiency Water storage efficiency become important when water

supplies are limited, when excessive time required adequate penetration of

water into the soil, also when sail problem exist, the water storage efficiency

should be kept eye to maintainflavourable salt balance.

Eg =

Es = Water storage efficiency percentage

Ws = water stored in root zone during irrigation

Wn - Water needed in root zone prior to irrigation.



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4.Water distribution efficiency:

It is the application of correct amount of water the field, also its uniform

distribution over field is important. Water efficiency indicates the extend to

which water is uniformly distributed along the run.

Ed (1-

) 100

Ed = water distribution efficiency percentage

= average depth of water stored along the run during irrigation

= average nururical deviation from

5.Water use efficiency:

Crop water use efficiency ratio of the crop yield 'y' to the amount of

water depletion by the crop, in the process of evapotraspination (ET) ratio of

crop yield.

Water use efficiency =

6.Field water use efficiency:

Ratio of crop yield (y) to the total amount of water used in field.

Field water use efficiency =

When,

WR = amount of water used in field.

How to increase the WUE:

The water utilized by crop is evaluated in terms of WUE. It can be

classified in to crop water use efficiency (Y/ET), field water use efficiency



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(Y/WR), physiologicalwater use efficiency (rate of photosynthesis / rate of

respiration). Ways to increase the WUEare,

1. Selecting proper crops and varieties. Crops differ widely in their dry

matterproduction. C4 plants like maize, sugarcane, sorghum have high

photosyntheticrate with high WUE compared to Ca plants like pulses,

oilseeds, wheat, rice etc.Within crop varieties differ in WUE. For

example in wheat, Kalyansona ishaving high WUE than Sonora-64.

2. Some agronomic practices like time of sowing, depth of sowing and

orientationof rows influence the WUE.

3. Climate influences the ET, yield and finally WUE

4. Irrigation practices like method of irrigation (among the surface

methodsfurrow and border strip method have high WUE), irrigation at

critical periods,proper scheduling of irrigation improves WUE.

5. Proper fertilizer application under adequate irrigation increases the yield

ofcrops and ultimately WUE.

6. Maintaining optimum plant population.

7. Proper management of pests and diseases.

Planting date:

In arid & semiarid regions planting date is an important cultural practice

to increase efficiency of water use. Main reason for using optimum rate for

sowing nsure good germination.

After the seed germinate, the moisture should be optimum for root

growth & root penetration to envelop more soil volume for nutrient uptake.

The dates indicate the right type of climate for shoot growth & optimum

utilization of moisture by root under normal rainfall condition.

Short season & early maturing crop species are after grown to escape the

drought of season.



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Competition for water starts when root system of crop & weed overlap.

Suitable technique for efficiency weed control have been developed

whichshould be available by increasing the water use efficiency of crop plants.

Efficient crop & water management includes judicious use of pesticides

& chemicals by proper use of from disturbing plane of nature by producing a

healthycrop plant.

Increasing water use efficiency in un irrigated area:

Includes tillage practious for moisture conservation are:

Deep tillage

Surface cultivation

Stubble mulching

Use of seedling equipments

Summer ploughing to control pest problem.



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Ex No. 12 ASSESSMENT OF QUALITY OF IRRIGATION WATER

The quality of water should be maintained in irrigation because, it

influencesthe chemical,&physical properties of soil, ultimately it influences the

productivity ofa crop. To assess the quality of irrigation water, the constituents

to be analysed are pH,Colour, EC, Soluble Sodium percentage (SSP), sodium

Adsorption Ratio (SAR), dissolved solids, such as Ca, Mg,

carbanates&Bicarbanates, cl, sulphate etc. We have to collect 1-2 liters of

water sample from the respective area in a polythene bottle to avoid chemical

reactions.

The quality of irrigation water is determined by the following

chemical characteristics:

1. Total concentration of soluble salts and total dissolved salts

2. Concentration of sodium relative or sodicity

3. Anionic composition of water, particularly consisting of bi-carbonate&

carbonate.

4. Concentration of boron, fluorine or other elements that may be toxic to

plant growth and retard the water uptake by a plant.

1. Total concentration of soluble salts:

The effect of salt on crop growth is believed to be mainly osmotic in

nature & hence related to total concentration rather than the concentration of

individual ionic species. There are two methods.

a) Total dissolved salts

b) Electrical conductivity.

Quality characterization of irrigation water based on EC.



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2. Concentration of Sodium:

a. Sodium absorption Ratio (SAR):

Sodium & its related elements (cations like Ca2+

& Mg2+

) SAR can be

calculated

SAR =

√

mq/litre

b. Soluble sodium percentage (SSP):

It is also similar to SAR, it can be calculated by,.

SSP=

3. Concentration of carbonates & bicarbonates:

4. Boron content

It is essential for plantgrowth, when Boron concentration is more 0.75ppm, it is

toxic, it is 2ppm, the affect will be severely toxic.

Management practices for quality of irrigation water:

1. Soil characters if soil texture is lighter the tolerance will be more.

2. Soil having high organic matter, the less tolerance, many crops shows

progressive decrease in yields with increase salinity.

3. Crops based on irrigation ovater, it is saline / any the crop can be grown

with tolerance limit.

4. Climatic condition - If the area is having high rainfall it leaches the

soils. Probably there should be furrow / sprinkler method of irrigation

should be used.



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Ex No. 13 IRRIGATION STRUCTURES

Irrigation structures are water distribution systems designed for easy and

efficient irrigation. These structures are used to convey, divert and control

irrigation water on the farm. Efficient structures will solve lalour, land and

water structures are

1. Conveyance structure

2. Water control and diversion structures

3. Crossing structures

4. Soil erosion control structures

1. Conveyance structures

They are the structures in which water is taken from the source through

canals, pipelines etc and applied to the field. They are two types of conveyance

structures.

a. Earthen channels:

It is the frequently used water conveyance channels on the farm can be

easily prepared by unskilled persons and require no equipments. It should be

build with stable side slopes and with strong banks the side slope should be flat

enough so that the banks will neither care in nor slide down when they are

saturated with water. The disadvantages are water loss is more (20-40%) weed

growth, sliting requires regular maintenance and it occupies more land area.

b. Lined channels:

The earthen channels are lined with impervious materials to prevent

excessive seepage loss and weed growth. The advantages are, water loss is

minimum, water move at faster rate, absence of weed growth, no wastage of



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land and maintenance costis less. The Disadvantages are, it needs high initial

investment. There are two types ofchannels.

i) Concrete lining:

Concrete lining is used as a permanent alternative for any other material.

A concrete mixture can be prepared by taking one part of cement, three part of

sand and four to five part of graded gravel from 1 to 3 cm size. The earthen

cannels of required size can be prepared, slopes can be tappered and

concentrate lining is made in order to avoid cracking. In alkali soil, alkali

resistant cement can be used.

ii) Brick/ stone masonry

Single layer brick or tiles or pebble may be used for lining channels. The

stones orbricks are laid flat on the compacted sides and bottom of the cannel

and joints are filled with cement mortar. The Mortar can be prepared by taking

one portion of cement with four portion of sand. The choice of brick / tiles /

stones depends on their availability and cost.

Brick / Stone / tile lined channels can be used when the discharge is 30

lps.

c) Procastconcrete channel sections:

They may be made in semi circular or half-pipes or U sections of one

matre or uore in length and 30-45 cm in diameter.

2. Water control and diversion structures:

These structures used for effective and easy control of irrigation water

on the farm. Besides, it checks erosion, minimize the water loss and save and

labour.



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i) Check gates:

Check structures consists of a masonry or metal wall build across the

channel and provided with a suitable check gate. Check gate is usually, a

precast made up of steel or wooden board and inserted into the slots on the

wall. Wooden boards are usually leaky and fanner shovels earth around them to

reduce leakage. Metal gates with specially designed rubber soil strips provide

tight water check the gate is provided with over or two handles depending on

the width of the gate to apply water from channels into a field it necessary to

naise the water level at least 8 to 12 cm above the ground surface.

ii) Check dams:

Canvas and plastic dams are supported on a pipe or wooden cross piece

with a loop at the bottom to anchor the dam. They can be removed after

irrigation, washed, and dried thus it can be used based on seasonal requirement.

iii) Diversion blocks:

They are constructed at the channel junction in order to carry water to

different farms or to different parts of the same farm. Two way or three way or

four way diversions are used depending upon the need.

iv) Turnouts:

The most common turnouts and siphon tubes may be either portable or

built in. It is used to take the water from channel into a field.

3. Crossing structures

To carry the irrigation water across the road hill sides and natural

depressions crossing structures are used. They are usually in the form of

straight pipe or anInverted siphon. Siphons are made up of concentrate or

vitrified clay pipes with suitable masonary structures at the inlet or outlet.



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4. Soil crosin control structures

When water is taken from uplands to the down slope severse soil erosion

occurs in the earthen channels the structures used to control erosion are.

i) Drop structures

Drop structures are used to discharge water in channel from a higher

level to a lower one a check gate is provided at the inlet of the drop structure of

control the water level at the upstream side of channel. Water enters the

structure through inlet passes through the vertical walls or the cut of walls and

falls into the stilling well the stilling basin controls the erosion and allows a

smooth flow.



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Ex: No: 14 DRAINAGE

It is the process of removal of excess water from the surface with a view

to avoid water logging and creates favorable soil conditions for optimum plant

growth water logging occurs due to heavy and containers rains excessive

application of water fauthery irrigation methods procolation and seepage four

nearby channels and reserviour. Presence of impervious layer and improper

layout leveling outlets etc water logging causes several changes in the soil they

are

a. Replacement of soil air with water and effect the availability of

oxygen to plant roots and microbes.

b. Lack of drainage promotes weed growth

c. Poor aeration reduces the availability of nutrients (Mg, Mn, Fe

&Zn)

d. Under aerobic conditions butric acid will be formed and it is

basic of plants.

e. It reduces the soil temperature.

f. Destruct the soil moisture

g. Reduces the activity of beneficial microbes

h. Difficult for cultural operations

i. Increases the incidence of pest and disease and some weeds

a. Uptake of water is slow.

b. Uptake of nutrients will be reduced

c. Shoot elongation to production of superdcal roots.

d. The proportion of arechymatous tissue in the roots which harmful

to plants.

Drainage structures should be



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i. Permanent

ii. Able to drain completely

iii. Minimum loss of cultivable area

iv. Minimum interference with cultural operations

Surface drainage:

Removing the excess water from the surface of the soils especially in

dry of sandy. Soils having less than 1.5% slope. The other types are

a.Lift drainage

To chain water from low lying area. Water can be derived by pumping

by mechanical means this method is costly.

b.Gravity drainage:

This system is practiced in wet land rice with gentle to moderate slope.

Water is drained from elevated areas to lower areas by gravity flow through the

outlet of various types. This method is less costly, easy and effective. Possible

to drain water from elevated areas only.

c.Field surface drainage:

The excess water received from the rain or irrigation is drained through

this method. The irrigated basins or furrows are connected with the drainage

channel at the lower elevation which is connected to main outlet and to form

pond from water harvesting.

d.Ditch Drainage: This method is suitable for rainfed crops ditches of

different dimension are constructed at distance to drain the excess water

accumulated on the surface.



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PRACTICAL MANUAL ON WATER - ISCA

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