Download - 56352-27253-SWC 302 - Lec 2&3 (1)
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Lecture 2
Irrigation - definition -necessity -advantage -
disadvantages.
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Irrigation
What? artificial application of water
Where to apply?
to the root zone of the crop
When to apply?
at right time
How much to apply?
in required quantity
What for?
for optimum crop yield
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Irrigation isartificial application of water
to the root zone of the crop
at right timein required quantity
for optimum crop yield.
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Irrigation may be defined as
the artificial application of
water to the root zone of the
crop at right time and inrequired quantity for the
optimum growth of agricultural
crops so as to get more crops
per unit of water used.
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FUNCTIONS:1. Supplies moisture to the soil essential for,
germination of seeds and chemical and bacterial
processes during plant growth.
2. Cools the soil and the surroundings thus making
the environment more favorable for plant growth.
3. Washes out or dilutes salts present in the soil.4. Softens the clods and thus helps in tillage
operations.
5. Enables application of fertilizers.
6. Reduces the adverse effects of frost on crops.7. Ensures crop success against short duration
drought.
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NECESSITY OF IRRIGATION
Throughout the crop period adequate
quantities of water is required near the
root zone of the plants for their growth Insufficient Rainfall
Uneven Distribution of Rainfall
Improvement of Perennial
Crops
Development of Agriculture in Desert
Area
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ADVANTAGES OF IRRIGATION
Stabilised Yield ofCrops
Protection from Famine
Improvement ofCash Crops
Prosperity ofFarmers Source of revenue
Navigation
Hydroelectric Power Generation.
WaterSupply General Communication
Development ofFishery
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DISADVANTAGES
Rising of WaterTable
Formation of Marshy Land
Dampness in Weather Loss of Valuable Lands
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Lecture 3
Duty of water - expression -
relationship between duty and
delta, Rooting characteristics
and Moisture use of crop
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MEASUREMENT OF WATER
Water is measured - at rests and in
motion.
Water at rest- reservoirs, ponds,tanks
volume units
- litre - l- cubic metre m3
- hectare- centimetre ha-cm
- hectare- metre ha-m.
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Water in motion - rivers, canals, pipeline,field channels
Rate of flow
- litre per second - lps- litre per hour - lph
- cubic metre per second - cumec
- cubic foot per second - cusec
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DUTY OF WATER(d ha/cumec)
The area that can be irrigated with a
continuous non-stop supply ofirrigation water at the rate of one
cumec or cusec throughout the base
period. It is expressed as acre/cusecor hectare/cumec.
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BASE PERIOD (B days)
The period over which irrigation
water is to be supplied for the
production of any crop.
Normally this is equal to the
period between the first and last
irrigation to a crop.
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DELTA ( cm)
The depth of water required by a
crop during the crop season tomeet its requirements. This does
not have any relevance to the
area of the cropped field. It isexpressed in mm or cm.
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RELATIONSHIP BETWEEN DUTY, DELTA AND
BASE PERIOD
Let be the depth of irrigation water required by a
crop in cm
B be the base period in days
d be the duty of water in ha/cumec.
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Then,
The volume of water required per ha of
cropped field = x 10000 = 100 m
100
The base period = B days
= B x 24 x 3600= 86400 B seconds
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The term duty explains that to irrigate dha of land water is to be supplied at the
rate of 1 cumec.
Therefore,To irrigate one ha the rate of flow required
= 1/d cumec.
The volume of water supplied @ 1/d
cumec over B days = 86400 B/d m3
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Equating the volume requiredand supplied,
we get,
100 = 86400 B
d
i.e., = 864 Bd
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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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GROSS DUTY OR INTAKE DUTY
Area irrigated by each cumec of water let
down at the head works of an irrigationsystem
NET DUTY OR DELIVERED DUTY.Area irrigated by each cumec of water
delivered at the field margin of an irrigation
system
Efficiency of the
irrigation system = Net duty /Gross duty.
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ROOTING CHARACTERISTICS AND MOISTURE USE OF CROP