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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