NAMITHA M RID NO:2015664502
M.TECH ,LWMEAEC&RI , KUMULUR
TNAU
IRRIGATION METHODS, SOIL-WATER-PLANT RELATIONSHIPS
IRRIGATION
Artificial application of water to arid land for growing crops
Supplementary to rainfall when it is either deficient or
comes irregularly or at unreasonable times
Irrigation engineering: Multi-disciplinary science
encompassing hydrology, agriculture, geology,
climatology, river engineering, agronomy, forestry, social
science, hydraulics, river soil mechanics, snow hydrology
and groundwater hydrology
NEED FOR IRRIGATION
1. Deficient rainfall:
Rainfall (cm) Irrigation requirement
100 Rainfall needs to be supplemented by irrigation
100-50 Rainfall is insufficient. Irrigation is essential.
50-25 Irrigation is essentially required.
Less than 25 No crop can be grown without irrigation.
Contd…
2. Non- uniformity of rainfall
3. Augmentation of crop yields
4. Exacting water requirement
5. Cash crops cultivation
6. Assured water supply
7. Orchards and gardens
ADVANTAGES OF IRRIGATION
a) Direct benefits
• Increase in food output through higher yield
• Cultivation of cash crops
• Land value appreciates manifold
• Protection from famine irrigation makes agriculture and
economy drought proof
• Prevention of damage through floods
• Hydel power generation at dam sites and canal falls
Contd…
Rise of subsoil water level in dry areas
Means of communication where navigation is possible in
canals
Revenue from recreational facilities
Fish and wild life preservation and development of pisciculture
Lowers production risks
Makes agriculture competitive and profitable
Reduced risks of crop failures
Improve the nutrition of people
Contd…
b) Indirect benefits
• Increase in GDP
• Increase in revenue from sales tax on food grains
• Increase in employment
• Improvement in groundwater storage
• Increase in value of land property
• General development of country
• Farm laborers are benefited who get higher wages
• Rise to whole array of agro-based industries
DISADVANTAGES OF IRRIGATION
Climate becomes damp and cold, causing malarial
diseases
Over-irrigation coupled with poor drainage in an area
where water-table is high leads to water logging of the
area, causes efflorescence
Low land revenue in certain cases
Excessive seepage from unlined canals leads to water
logging of lands adjacent to canals
SOIL-WATER – PLANT RELATIONSHIP
Water is the basic input influencing crop
production
The amount of water required for a given
crop depends on:
State of development of soil
Quantity and type of fertilizer given
Quality of water used
Climatic conditions
Contd…
Soil- water- plant relationship Process that
requires to be regulated for maximization of yields
with a given unit of water
Understanding of Soil- Water- Plant relationship is
essential in order that water management principles
are applied to various climatic, soil and cropping
regions of both rain fed and irrigated lands
Contd…
A. Soil factors
a) Infiltration:-
• Influences selection of irrigation methods, slope
needed for the land, length of run, irrigation application
time etc.
• Soil water parameters affecting infiltration rates:-
Texture, Structure, Bulk Density, Sodium salts, Crop
grown, Irrigation water, Temperature, Tillage and Water
in soil
Contd…
b) Permeability:-
• Depends on soil texture and structure, presence of plant roots
and changes in temperature of water
• K= QL/A(H1-H2) where, Q= Discharge/ unit time
A= Cross sectional area through which water flows
H1-H2 = Hydraulic head L = Percolation path length
Contd…
Soil
Gravel (clean)
Coarse sand (clean)
Sand (mixture)
Fine sand
Silty sand
Silt Clay
K 1.0 or more
1.0-0.01
.01-.005 .05-.001
0.002-0.0001
0.0005-0.00001
0.00001 or lesser
Measured using Constant head permeameter and Variable
head permeameter
Contd…
c) Drainability and Leachability:-
• Principal factors in predicting the drainability of a
soil is its permeability and hydraulic gradient
• Leachability is directly related to drainability
d) Erodibility
Contd…
B. Plant factors
a) Rooting characteristics:-
• High water table limits the root growth due to lack of
sufficient aeration
b) Evapo-transpiration:-
• General rule is that 40,30,20 and 10 percent of the total ET
is removed respectively from each successively deeper
one-quarter of the rooting depth
Contd…
c) Effect of soil water level on crop growth and yield:-
• Crop growth and transpiration generally decreases as
the wilting point approaches
• The point at which growth or transpiration of a plant is
retarded for want of soil water, crop characteristics, low
or high evaporative demand etc.
Contd…
C. Water factors
a) When to irrigate:-
• Generally irrigation shall start when 50%, but not over 60% of
the available moisture is used from the root zone
• Design frequency = (Field capacity of soil in
effective crop root zone- moisture
content of the same zone at the
starting of irrigation)/ Moisture
use of root of crop in peak period
Contd…
b) How much water to apply:-
• The amount of water to be replaced is usually 40-50% of the
available water in the root zone of the soils having a uniform
available water capacity with depth
c) Water application method:-
• Influenced by quantity of available water supply, type of soil,
topography and crops to be grown
• Methods include controlled surface flooding method, sprinkler
method and drip method.
METHODS OF IRRIGATION
A. Sub- surface irrigation
Water applied beneath the ground by creating and
maintaining an artificial water table
30-75 cm below the ground surface
Consists of main field ditches, laterals, laid 15-30m
apart
Open ditches, mole drains or tile drains
Advantages of sub-surface irrigation
Minimum water requirement for raising crops and high yield
Minimum evaporation and deep percolation losses
Most economical method of irrigation and suitable for most crops
Involves no wastage of land
No interference in free movement of farm machinery
Cultivation operations can be carried out without concern for the
irrigation period
Little field preparation and labor
Disadvantages of sub-surface irrigation
Requires a special combination of natural conditions
There is danger of development of water logging
Possibility of choking of the pipe laid underground
High cost
Classification of sub-surface irrigation
1. Natural sub-irrigation:
• Applicable to low lying lands where the water table is high
• Water table is charged by seepage from irrigation canals
2. Artificial sub-irrigation:
• Very expensive method
• Water under pressure provided to crops by capillarity
through a network of buried perforated pipes
B. Surface irrigation
Most common type of irrigation
Water is applied to the field in varied quantities at different
times
Flow remains unsteady
Diverting a stream of water from the head of a field into
furrows or borders and allows to flow downward
Supplemented with efficient water disposal system
Advantages of surface irrigation
Allows use of machinery for land preparation,
cultivation and harvesting
Helps to store the required amount of water in the
capillary zone of the soil for supply to the root zone of
plants
Disadvantages of surface irrigation
Greater loss of water by surface runoff and deep percolation
Larger requirement of water per unit area
Water is lost in infiltration and deep percolation
Low efficiency due to imperfect control over the water flow
Inferior quality crops with a low yield
Wasteful use of water
Costly and time consuming land preparation
Classification of surface irrigation
1. Flooding method:
• Water is allowed to cover the surface of land in a
continuous sheet
• The flooding may be:
a) Wild flooding (uncontrolled flooding) :
• Primitive and most inefficient method
• Water is spread over the smooth or flat field without
much control over the flow or prior preparation
Contd…
• Water distribution is quite uneven
• Advantage: Low cost and does not interfere with tillage
Suitable for all medium to fine texture soils
• Disadvantage: Wasteful use of water
Non-uniform distribution of water
Excessive soil erosion on steeper slopes
Require drainage arrangement to reduce ponding
Contd…
b) Controlled flooding :
i. Free flooding (ordinary flooding) : Land is divided into
plots or kiaries of suitable size depending on porosity of
soil
Water is spread over the field from water course
Spreading may vary from less than 15m to more than
60m
Contd…
ii. Border flooding: Field is divided into narrow strips by low
parallel ridges on the sides
Width if strip: 5-15m ; Length of strip: 60-100m for sandy
loam, 100-120 for medium loam, 150-300 for clay loam
Longitudinal gradient: 0.02-0.05% for clay to clay loam,
0.20-0.40% for medium loam, 0.25-0.60% for sandy
loam to sandy soil
Contd…
iii. Check flooding: Applying water to relatively level check
basins enclosed by small bunds
Size of check basin: 3*2m to 3*3m or even large
iv. Contour lateral method: Best suited to steeper terrain
Dense network of contour laterals are laid with spacing
15-50m
Adopted mostly in close growing crops on sloping lands
Contd…
v. Zig zag method: Suitable for relatively level fields
Unsuitable for mechanical farming operations
Land is divided into square or rectangular plots; each
plot further sub divided with low bunds
vi. Basin flooding: Check method of flooding adapted to
orchards
Basins are made around one or more trees depending
on the soil condition and topography
adapted essentially to flat lands
Contd…
b)Contour farming:
• Adapted to hilly areas with steep slopes and quick falling
contours
• Land is divided into longitudinal curved plots, the bunds of
the plots following the contours
• Reduces runoff and soil loss
Contd…
c) Furrow method:
• Used for row crops
• A furrow consists of a narrow ditch between the rows of
crops
• Water is applied in small streams between rows of crops,
grown on ridges or in furrows
C. OVER HEAD IRRIGATION (SPRINKLER IRRIGATION)
• Simulates natural rainfall to spread water in the form of rain
uniformly over the land surface
• Water is spread in uniform pattern and rate less than the
infiltration rate of the soil
• No land leveling is required
• Suitable for all types of soil and almost all crops
• Not recommended for crops having high water requirement
(eg. Rice, jute )
Contd…
Helps to conserve water up to 50%
Can irrigate 2 to 3 times the area compared to surface
irrigation
Tried on large scale in Tamil Nadu, Karnataka, Haryana and
Punjab
Factors governing selection of sprinkler
i. Land of undulating topography (sandy dunes)
ii. Land of steep slopes and easily erodible soils by surface
irrigation
iii. Land with shallow soil cover, sandy soils or soils with
high infiltration rate
iv. Highly porous or relatively impermeable soils unsuitable
for proper water distribution by surface irrigation methods
Contd…
v. Limited water supply and high cost of water as in lift
irrigation
vi. Need for light and frequent irrigation
vii. Costly and unreliable farm irrigation
viii. Lands need to be brought into production quickly
without waiting for land development and construction
of channels
Sprinkler irrigation system
Water pumped under pressure, carried through high
pressure main line, let out through sprinkler nozzles placed
at regular intervals on lateral lines forming a gentle rain
Considerations: Agro-climatic conditions, general land
condition, maximum difference in elevation, cropping
pattern, irrigation and cover crop requirements, matching
pump and power unit, water supply source etc.
Contd…
Layout:-
• Depends on the slope and size of the farm and
location of water source
• Economical when source of water is at the centre of
the area
• Distance between laterals= 12m
• Distance between 2 sprinklers= 12m
Contd…
Water application rate:-
• Less than the infiltration capacity of the soil to be irrigated
• Depends on nature of soil, crop and topography
• Varies from 0.25 cm/hr for clay to 5.5 cm/hr for very light soils
• Application rate= (Discharge(lps)* 282.6)/(spacing
of sprinkler(m)* spacing of
laterals(m))
Contd…
Water application in each irrigation:-
• Determined by using not more than 50% available moisture in
the soil
• Area to be irrigated depends on type & pattern of sprinkler
and operating pressure adopted
Sprinkler losses:-
• Depends on wind velocity, temperature, fineness of spray,
humidity , soil texture and vegetation cover
Contd…
Capacity of the system:-
• To meet the peak demand of the area under crops during the
hottest and driest periods
• Capacity of pipe system depends on the rate of application of
water and the area to be irrigated in one setting
• System capacity, Q= (A*D*27.8)/(I*H*E)QDischarge (lps) ; AArea(ha)DDepth of water application(cm)IInterval between successive irrigation (days); HOperating hours (hr/day) ; EField application efficiency
Contd…
Operating pressure:-
• Size of droplets is limited by small nozzles
• Pressure: 2.75kg/cm2 for 3mm nozzle with additional 0.35 kg/cm2
pressure for each 0.75 mm increase in nozzle size
• Water pressure: 0.5 to 10 kg/cm2
Sprinkler spacing and distribution pattern:-
• Properly maintained for adequate water distribution
• Overlap of sprinkler throw is adequate
• Maximum move interval =18m
Contd…
Main and lateral pipe sizes:-
• Determined by the maximum rate of flow and nature and length of
pipes involved
• Variation of pressure in the lateral, due to friction loss= 20% of
operating head
• Pressure loss in main= 0.7kg/cm2
Pumping unit:-
• Selection of the pumping set is made from the characteristic
curve of the pump set supplied by the manufacturer
Contd…
Discharge of sprinkler:-
• Discharge of a sprinkler, Q= (Sl*Sm*R)/360, lps
Sl= Spacing (m) of sprinkler along laterals
Sm= Spacing (m) of laterals along the mains
R= Optimum application rate (cm/hr)
• Discharge of sprinkler nozzle, q= Ca√ (2gh), m3/s
a= Sectional area of the nozzle (m2)
H= Pressure head of nozzle (m) ; C= Coefficient of discharge
Contd…
• Water spread of sprinkler, R= 1.35 √ (dh)
R= Radius of the wetted area covered by sprinkler (m)
d= Diameter of nozzle (m)
H= Pressure head at nozzle (m)
Types of sprinkler systems
Based on portability:
1. Fully portable system
2. Semi-portable system
3. Permanent system
4. Semi- permanent sprinkler system
1. Sprinkler hop system
2. Pipe grid system
3. Hose pull system
Contd…
Based on spraying pattern:
1. Rotary head or revolving system
2. Perforated sprinkler system (perfo-spray system)
Based on arrangement of spraying:
1. Fixed head type
2. Rotary type
Sprinkler losses and efficiency
Sprinkler Losses:
• Losses: Evaporation, some deep percolation, drift of spray due
to wind, conveyance loss (negligible) etc.
• Evaporation loss is minimum at night and maximum at afternoon
• Windy and hot weather conditions increases losses
Efficiency:
• Varies according to climatic conditions
• 60% on hot day, 70% in moderate and 80% in humid climate
Advantages of sprinkler irrigation
• Saves water, irrigates more land
• Low water loss
• Effective water management
• Saving in land
• Saving in fertilizers
• Land leveling not necessary
• Soil conserved
• Soil condition is maintained
Contd…
• Soil is stabilized
• Better seed germination
• Frost control
• Instant irrigation
• Use of limited source
• Uniform application
• Controls climate
• Sport grounds
Contd…
Free aeration of root zone
Poor soils irrigated
Drainage problems eliminated
Improved soil fertility organism
Weeds and pests controlled
High crop yield and quality
Reduced labor requirement
Peoples participation
Limitations of sprinkler irrigation
• High initial cost
• Poor application efficiency in windy weather and high
temperature
• Higher evaporation losses in spraying water
• Not suitable for jute or rice
• Cannot be used with rotational supply systems of water
distribution in canal irrigated areas
• Water supply free of solids and debris is needed
Contd…
• Assured source of surface or groundwater supply is needed
• Cannot be used in low infiltration rate soils
• High power requirement
• Uniformity coefficient is low
• Poor distribution efficiency
• Use of recycled water is restricted for health reasons
• Equipment need careful handling
• Nozzles need screened water supply
D. BURIED IRRIGATION
• Substitute of canals by pipelines
• Water is delivered by a canal from the source to the irrigation
area
• Inside area is distributed by gravity pressure pipelines
• Water supplied to field pipelines by pumping: 400m spacing
between pipelines
• Field pipelines has hydrants, sprinklers or watering machines
Contd…
• Field pipelines: HDPE pipes 10-30cm in diameter at 0.75-1.25m
depth
• Operating under 6 atm pressure
• Water flows in pipelines due to the head created by the natural
gradient (>0.003)
• Maximum velocity of flow is not to exceed 3.5 m/s
• Non silting velocity,
V= (v2f)/( 0.0000232 u0.25 *8g) , kg/m3 v = current velocity of flow(m/s); u= fall velocity of sediment (mm/s)
Advantages of buried irrigation
It is a reliable method of irrigation for the control of:
Water losses from irrigation canal
Water logging
Salinization of lands
E. DRIP IRRIGATION
• Also known as Trickle irrigation
• Water is applied in the form of drops directly to the plants
through drip nozzles
• Water drops into the soil slowly and frequently to keep the
soil moisture within the desired range
• Particularly suited for soils with very low and very high
infiltration rates
• Maximize the water saving
Contd…
• Involves lateral spread of water on the surface by
conducting the water under pressure to a relatively closely
spaced grid of outlets and discharging water at virtually
zero pressure
• Irrigation is done through drippers fitted on small diameter
lateral lines, delivers water to the crop root zone
• Water is pre filtered for removing the suspended impurities
Drip irrigation system-components
1. Head tank:
• Water lifted is stored in head tank (3*3*3 m) resting on a raised
platform to maintain a pressure head of 3-5m
• Functions: Regulates the pressure and amount of water applied
Filter the water
Add nutrient material
Contd…
2. Main lines:
• Plastic main lines deliver water to sub mains
• 20-40mm diameter suitable for desired discharge
3. Laterals:
• Sub mains delivers water to laterals which I turn convey it to
emitters
• 10-20mm diameter, generally placed along plant row
• Perforated at a distance equal to the plant spacing, usually
20cm for vegetables and cotton
Contd…
4. Emitter:
• Applies water to the root zone
• Very low rate of flow, usually 1-9 lph
5. Chemical injection unit:
• To inject chemicals such as chlorine
• To ensure fertigation
6. Monitoring and control equipment:
• Includes controller, pressure gauges, tensiometers and a flow
meter , valves etc.
Contd…
7. Fertilizer tank:
• Tank filled with concentrated nutrient solution connected to
the head directly in front of filter unit
• Nutrient solution is introduced into the water flowing to the
trickle network
• Fertilizer dispenser injects fertilizers into the system at a
predetermined rate
Design of drip irrigation system
• In plantations, trickle lines are 6m apart with 3 emitters at
each point
• Design capacity should satisfy the peak irrigation water
demand of each and all crops to be irrigated within the
design area
Contd…
1. Irrigation water requirement:
• Mainly influenced by the crop ET rate, irrigation interval and
the water application uniformity
2. Emitter discharge ratio:
• For point source emitters, the discharge is < 12lph for single
outlet emitters
• For line source emitters, it is <12lph/m of the lateral
Contd…
3. Number and spacing of emitters:
• Depends on the emitter discharge rate, system capacity, soil
WHC, depth of irrigated crop root zone, lateral spread of water
from the emitters and desired water application uniformity
4. Operating pressure:
• Water is fed at a reduced pressure of 0.5-0.7 kg/cm2 using
pressure reducer
• Pressure in laterals= 0.15-0.20 kg/cm2 (low) to
1.0-1.75 kg/cm2(high)
Contd…
5. Water application uniformity:
• Affected by the operating pressure, emitter spacing, land slope,
pipeline size, emitter discharge rate and emitter variability
• Design emission uniformity,
Eu= 100 (1.0-(1.27Cv/n))(qm/qa), %Cv= Manufacturers coefficient of variation qm = Minimum emitter discharge rate for the minimum pressure in the
system (lph)qa = Average or design emitter discharge rate (lph)
• Recommended range of Eu= 95-70%
Contd…
6. Laterals:
• Usually 10-20mm in diameter and 300mm long
• Laid down slope for slopes < 5%
7. Varying size of outlet openings:
• Head loss occurring in a segmental pipe length l is:
hf = (flv2 )/ (2gd)
• The pressure available at any downstream section goes on
falling the size of the openings spaced at equal intervals should
be monotonically increased for getting a constant discharge
Advantages of drip irrigation
• Water saving
• Reduced losses
• Uniform water distribution
• Over-irrigation avoided
• No land leveling
• Application rate to suit need
• No soil erosion
• Weed control
• Land saving
Contd…
• Nutrient preservation
• Salinity control
• Marginal soil
• Use of unsuitable supply
• Less labor cost
• High surface temperature
• Leaf shedding minimized
Contd…
• Soil in most congenial form
• Uninterrupted cultivation operation
Higher yield
Improved water penetration
Energy saving
Disadvantages of drip irrigation
• High initial cost
• Drippers are susceptible to blockage
• High skill is required for design, installation, operation and
maintenance
• Not all crops respond to localized wetting only
• Sometimes poor anchorage of roots
• Proper management is required in saline soils
• Application of insoluble or slightly soluble fertilizers through the
flow is not readily possible
F. SEEPAGE LINE IRRIGATION
• Relatively new cost effective concept in irrigation
• Provides limited but assured irrigation facilities to crops
during critical times
• Seepage from wells were collected by pipelines to a central
pond
• Stored water is supplied to individual farms through
pipelines
G. SUCTION IRRIGATION
• A variant of drip irrigation
• Uniform and controlled water is supplied to the root zone of a
plant automatically
• Spindle shaped burnt clay emitters with neck on either side are
used
• Water seeps out of the wall of porous emitters and the plant
receives water directly at the root zone
REFERENCE
https://www.google.co.in/
R. K. , Sharma, T. K. , Sharma, Irrigation Engineering, Chand
publications.
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