Club of Rome: Eco-nomics for an Ecological Civilization
New
1. Irrigation Methods are mainly classified into :
1. Surface Irrigation or Gravity Irrigation
2. Subsurface Irrigation or Sub-irrigation
3. Sprinkler or overhead irrigation
4. Drip or Trickle irrigation
2. SURFACE IRRIGATION
Irrigation water flows across the field to the
point of infiltration
Primarily used for field crops and orchards
Water is applied to the soil surface and the water
flows by gravity either through furrows, strips or
basins.
Water is applied from a channel located at the
upper reach of the field.
3. SURFACE IRRIGATION
Loss of water by conveyance and deep
percolation is high and the efficiency of
irrigation is only 40-50% at field level in
surface method of irrigation.
Properly constructed water distribution
systems to give sufficient control of water
to the fields
And effective land preparation to permit
uniform distribution of water over the field
are very important.
4. Water is applied to the field in either the controlled or
uncontrolled manner.
Controlled: Water is applied from the head ditch
and guided by corrugations, furrows, borders, or
ridges.
Uncontrolled: Wild flooding.
Surface irrigation is entirely practised where water is
abundant.
Low initial cost of development is later offset by high
labour cost of applying water.
Deep percolation, runoff and drainage problems
7. Furrow irrigation - in which the water poured on
the field is directed to flow through narrow
channels dug between the rows of crops, instead of
distributing the water throughout the whole field
evenly.
The furrows must all have equal dimensions, in
order to guarantee that the water is distributed
evenly.
Like flood irrigation, furrow irrigation is rather
cheap in areas where water is inexpensive.
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11. In furrow irrigation, only a part of the land surface
(the furrow) is wetted thus minimizing evaporation
loss.
Irrigation can be by corrugation using small irrigation
streams.
Furrow irrigation is adapted for irrigating on various
slopes except on steep ones because of erosion and
bank overflow.
12. There are different ways of applying water to the furrow.
siphons are used to divert water from the head ditch to the furrows.
There can also be direct gravity flow whereby water is delivered
from the head ditch to the furrows by cutting the ridge or levee
separating the head ditch and the furrows.
Gated pipes can also be used. Large portable pipe(up to 450 mm)
with gate openings spaced to deliver water to the furrows are used.
Water is pumped from the water source in closed conduits.
The openings of the gated pipe can be regulated to control the
discharge rate into the furrows.
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18. In this, Parallel ridges are made to guide a sheet of
flowing water when the water moves down the slope.
The field is divided into several long parallel strips
called borders that are separated by low ridges.
Field should be even surface over which the water
can flow down the slope with a nearly uniform depth.
Every strip is independently irrigated by turning a
stream of water at the upper end.
19. Then water spreads and flows down the strip in a thin
sheet.
Water moves towards the lower end without erosion
covering the entire width of the border.
Sufficient moisture is provided to the soil to entire
length of the border.
Border method is suitable for most of the soils, while
it is best suited for soils having moderately low to
high infiltration rates.
However, it is not suitable for course sandy and clay
textured soils.
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Basin method of irrigation is adopted mainly in
orchards.
Usually round basins are made for small trees and square
basin for large trees.
These basins allow more water to be impounded as the
root zones of orchard plants are usually very deep.
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Each basin is flooded and water is allowed to infiltrate
into the soil.
Based on type of crop and soil, nearly 5-10 cm depth of
water may be needed for every irrigation.
The advantage of basin method is that unskilled labour
can be used as there is no risk of erosion.
Disadvantages : there is difficulty in using modern
machinery and it is also labour intensive.
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27. Basin irrigation is suitable for many field crops.
Rice grows best when its roots are submerged in water
and so basin irrigation is the best method to use for this
crop.
Other crops which are suited to basin irrigation include:
Pastures, e.g. alfalfa, clover;
Citrus, banana;
Crops which are broadcast, such as cereals, and
To some extent row crops such as tobacco.
28. Most common among surface irrigation
Suitable for close growing crops like
groundnut, wheat, finger millet, pearl millet,
paragrass etc.
In this method field is divided into small plots
surrounded by bunds on all four sides.
Water from head channel is supplied into the
field channel one after the other.
Each field channel supplies water to two rows
of check basins and water is applied to one
basin after other.
29. In this, field is laid out into long, narrow,
strips, bordering with small bunds.
Most common size of strips are 30-50 m
length and 3-5 m width.
Borders are laid out along the general
slope.
Water from the channel is allowed into
each strip at a time.
This method is suitable for close growing
crops and medium to heavy textured
soils.
Not suitable for sandy soils.
30. It should be applied only to flat lands that
do not concave or slope downhill so that
the water can evenly flow to all parts of the
field.
Yet even so, about 50% of the water is
wasted and does not get used by the crops.
Some of this wasted water accumulates at
the edges of a field and is called run-off.
In order to conserve some of this water,
growers can trap the run-off in ponds and
reuse it during the next round of flood
irrigation.
31. In flood irrigation, a large amount
of water is brought to the field
and flows on the ground among
the crops.
In regions where water is
abundant, flood irrigation is the
cheapest method
This low tech irrigation method is
commonly used by societies in
developing countries.
32. However a large part of the wasted water can not
be reused due to massive loss via evaporation and
transpiration.
One of the advantages of flood irrigation is its
ability to flush salts out of the soil, which is
important for many saline intolerant crops.
However, the flooding causes an anaerobic
environment around the crop which can increase
microbial conversion of nitrogen from the soil to
atmospheric nitrogen, or denitrification, thus
creating low nitrogen soil.
Surge flooding is an attempt at a more efficient
version of conventional flood irrigation in which
water is released onto a field at scheduled times,
thus reducing excess run-off.
33. - Irrigation to crops by applying water
from beneath the soil surface either by
constructing trenches or installing
underground perforated pipe lines.
In this system, water is discharged
into trenches.
And allowed to stand during the whole
period of irrigation for lateral and
upward movement of water by
capillarity to wet the soil between the
trenches.
34. Conditions that favor subsurface irrigation
An impervious subsoil at a depth of 2 m or more.
A very permeable subsoil of reasonably uniform texture
permitting good lateral and upward movement of water.
Permeable loam or sandy loam surface soil.
Uniform topographic conditions and moderate slope.
Existence of high water table.
Irrigation water is scarce and costly.
Soils should be free of any salinity problem.
It must be ensured that no water is lost by deep
percolation.
Subsurface irrigation is made by constructing a series of
ditches or trenches 60 to 100 cm deep.
Width of the trenches is about 30 cm and vertical.
Spacing between the trenches varies between 15 to 30 m
depending on soil types and lateral movement of water in
soils.
35. Various types of crops, particularly with
shallow root systems are well adapted to
subsurface irrigation system.
Wheat, potato, beet, peas, fodder crops etc.
Advantages
Maintenance of soil water at favorable tension
Loss of water by evaporation is held at
minimum
Can be used for soils with low water holding
capacity and high infiltration rate where
surface irrigation methods cannot be adopted
and sprinkler irrigation is expensive.
36. Presence of high water table.
Poor quality irrigation water cannot be
used-good quality water must be
available.
Chances of saline and alkali conditions
being developed by upward movement
of salts with water.
Soils should have a good hydraulic
conductivity for upward movement of
water.
37. Sprinkler irrigation is a method of applying irrigation
water which is similar to natural rainfall.
Water is distributed through a system of pipes usually
by pumping.
Water under pressure is carried and sprayed into the air
above the crop through a system of:
Overhead perforated pipes, nozzle lines, or through
nozzles fitted to riser pipes attached to a system of
pipes laid on the ground.
Nozzles of fixed type or rotating under the pressure of
water are set at suitable intervals in the distribution
pipes.
Sprayed water wets both the crop and the soil and,
hence, has a refreshing effect.
Water is applied at a rate less than the intake rate of
soil so that there is no runoff.
Measured quantity of water is applied to meet the soil
water depletion.
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40. Sprinkler irrigation is suited for most row, field
and tree crops and water can be sprayed over or
under the crop canopy.
Large sprinklers are not recommended for
irrigation of delicate crops such as lettuce because
the large water drops may damage the crop.
Suitable slopes
Sprinkler irrigation is adaptable to any farmable
slope, whether uniform or undulating.
Lateral pipes supplying water to the sprinklers
should always be laid out along land contour.
This will minimize the pressure changes at the
sprinklers and provide a uniform irrigation.
41. Sprinklers are best suited to sandy
soils with high infiltration rates
although they are adaptable to most
soils.
Application rate from the sprinklers (in
mm/hour) is always chosen to be less
than the basic infiltration rate of the
soil - so that surface ponding and
runoff can be avoided.
Sprinklers are not suitable for soils
which easily form a crust.
42. A typical sprinkler irrigation system consists of
the following components:
Pump unit
Mainline
Laterals
Sprinklers
Suitable irrigation water
A good clean supply of water, free of suspended
sediments, to avoid problems of sprinkler
nozzle blockage and spoiling the crop by
coating it with sediment.
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Sprinkler irrigation (cont..)
• Uniform application by “artificial rain”
• Good application efficiencies (0.7 – 0.8)
– dependent on wind, temperature, humidity
• Fairly terrain independent (but design must
take terrain into account)
• Can have a low labour content
However,
• High(ish) investment cost
• High maintenance cost due to pumping
• Can be complex to run
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Sprinkler irrigation: Criteria
• Must permit cost recovery within one to two
years (and double investment in a short time)
• Must be suitable for use on small and irregular
shaped plots
• Must require only simple maintenance and tools
• Have a low risk of component failure
• Be simple to operate
• Be durable and reliable – able to withstand
rough and frequent handling without serious
damage
49. A typical drip irrigation system is
shown in Figure 61 and consists
of the following components:
Pump unit
Control head
Main line
Laterals
Emitters or drippers.
50. Pump unit takes water from the source and
provides the right pressure for delivery into the
pipe system.
The control head consists of valves to control the
discharge and pressure in the entire system.
It may also have filters to clear the water.
Common types of filter include screen filters and
graded sand filters which remove fine material
suspended in the water.
Some control head units contain a fertilizer or
nutrient tank.
These slowly add a measured dose of fertilizer into
the water during irrigation.
This is one of the major advantages of drip
irrigation over other methods.
51. Supply water from the control head into the fields.
They are usually made from PVC or polyethylene hose and
should be buried below ground because they easily
degrade when exposed to direct solar radiation.
Lateral pipes are usually 13-32 mm diameter.
Emitters or drippers are devices used to control the
discharge of water from the lateral to the plants.
They are usually spaced more than 1 metre apart with one
or more emitters used for a single plant such as a tree.
For row crops more closely spaced emitters may be used to
wet a strip of soil.
Many different emitter designs have been produced in
recent years.
The basis of design is to produce an emitter which will
provide a specified constant discharge which does not vary
much with pressure changes, and does not block easily.
52. The water savings that can be made using drip
irrigation are the reductions in deep percolation,
in surface runoff and in evaporation from the
soil.
These savings, it must be remembered, depend
as much on the user of the equipment as on the
equipment itself.
Drip irrigation is not a substitute for other
proven methods of irrigation.
It is just another way of applying water.
It is best suited to areas where water quality is
marginal, land is steeply sloping or undulating
and of poor quality, where water or labour are
expensive, or where high value crops require
frequent water applications.
