Lecture 2Irrigation - definition -

necessity -advantage - disadvantages.

IrrigationWhat? artificial application of water Where to apply? to the root zone of the cropWhen to apply? at right timeHow much to apply? in required quantityWhat for?for optimum crop yield

Irrigation is •artificial application of water •to the root zone of the crop •at right time •in required quantity •for optimum crop yield.

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.

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.

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

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

DISADVANTAGES

• Rising of Water Table

• Formation of Marshy Land

• Dampness in Weather

• Loss of Valuable Lands

Lecture 3Duty of water - expression -

relationship between duty and delta, Rooting characteristics

and Moisture use of crop

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.

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

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.

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.

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.

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 daysd be the duty of water in ha/cumec.

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

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 @ 1/d cumec over B days = 86400 B/d m3

Equating the volume required and supplied, we get,100 ∆ = 86400 B

di.e., ∆ = 864 B

d

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

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.

ROOTING CHARACTERISTICS AND MOISTURE USE OF CROP