Irrigation - definition - necessity -advantage - disadvantages.

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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 is
• artificial application of water
• to the root zone of the crop
• at right time
• in 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 in required quantity for the
optimum growth of agricultural crops so as to get
more crops per unit of water used.
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• FUNCTIONS
• Supplies moisture to the soil essential for,
  germination of seeds and chemical and bacterial
  processes during plant growth.
• Cools the soil and the surroundings thus making
  the environment more favorable for plant growth.
• Washes out or dilutes salts present in the soil.
• Softens the clods and thus helps in tillage
  operations.
• Enables application of fertilizers.
• Reduces the adverse effects of frost on crops.
• 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 of Crops
• Protection from Famine
• Improvement of Cash Crops
• Prosperity of Farmers
• Source of revenue
• Navigation
• Hydroelectric Power Generation.
• Water Supply
• General Communication
• Development of Fishery

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DISADVANTAGES

• Rising of Water Table
• 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 of
irrigation water at the rate of one cumec or
cusec throughout the base period. It is expressed
as acre/cusec or 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 to meet its
requirements. This does not have any relevance to
the area of the cropped field. It is expressed 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 d ha 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 _at_ 1/d cumec over B days 86400
B/d m3
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Equating the volume required and supplied, we
get, 100 ? 86400 B d i.e., ?
864 B d
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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
irrigation system 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