1.6 Irrigation

Submitted by superadmin on 6 May, 2023 - 22:13

NCERT Class 8 Science Textbook for Blind Students made Screen Readable by Dr T K Bansal.

All living beings need water to live. Water is important for proper growth and development. Water is absorbed by the plant roots. Along with water, minerals, and fertilizers are also absorbed. Plants contain nearly 90% water. Water is essential because germination of seeds does not take place under dry conditions. Nutrients dissolved in water are transported to each part of the plant. Water also protects the crop from both frost and hot air currents. To maintain the moisture of the soil for healthy crop growth, fields have to be watered regularly.

The supply of water to crops at regular intervals is called irrigation. The time and frequency of irrigation varies from crop to crop, soil to soil and season to season. In summer, the frequency of watering is higher. Why is it so? Could it be due to the increased rate of evaporation of water from the soil and the leaves?

I am very careful this year about watering the plants. Last summer my plants dried up and died.

Sources of irrigation :

The sources of water for irrigation are - wells, tubewells, ponds, lakes, rivers, dams and canals.

Traditional Methods of Irrigation:

The water available in wells, lakes and canals is lifted up by different methods in different regions, for taking it to the fields.

Cattle or human labour is used in these methods. So these methods are cheaper, but less efficient. The various traditional ways are:
(i) moat (pulley-system)
(ii) chain pump
(iii) dhekli, and
(iv) rahat (Lever system)
[Figs. 1.4 a, b, c, d.

Pumps are commonly used for lifting water. Diesel, biogas, electricity and solar energy is used to run these pumps.

Figure 1.4 (a) : Moat

this is a pulley system the bucket is tie with rope to pull the water bucket

Figure 1.4 (b) : Chain pump

A pump consisting of a sprocket-operated endless chain fitted at close intervals with disks that lift the water by moving rapidly through a pipe in the direction of the desired flow

Figure 1.4 (c) : Dhekli

This method consists of a lever-rod rocking over the top of a vertical upright post. A suitable counter weight is tied on one side of the lever and a bucket is suspended from the other end into the well. Length of the lever rod on the side of the bucket is longer than that on the side of counter­weight. The bucket when filled is lifted a little to set the lever action. The bucket full of water moves up automatically due to moment of the counter weight

Figure 1.4 (d) : Rahat

This method was very common in Northern India. Still it can be noticed in U.P., Haryana and Punjab. Persian wheel consists of an arrangement of wheels and gears run by bullocks. An endless chain of several buckets is put on a big wheel. The lower end of chain of buckets remains under well water.</p> <p>As the wheel is moved by bullocks through a system of gears, the buckets filled with water come to the top and discharge water into a trough from where water flows to the fields. In this case pair of bullocks moves on circular path. By this method 3-5 hectare of land can be irrigated.

Modern Methods of Irrigation

Modern methods of irrigation help us to use water economically. The main methods used are as follows:

(i) Sprinkler System:
This system is more useful on the uneven land where sufficient water is not available. The perpendicular pipes, having rotating nozzles on top, are joined to the main pipeline at regular intervals. When water is allowed to flow through the main pipe under pressure with the help of a pump, it escapes from the rotating nozzles. It gets sprinkled on the crop as if it is raining. Sprinkler is very useful for lawns, coffee plantation and several other crops [Figure 1.5 (a)].

Figure 1.5 (a) : Sprinkler system

Figure shows a 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. It is then sprayed into the air through sprinklers so that it breaks up into small water drops which fall to the ground.

(ii) Drip system :
In this system, the water falls drop by drop directly near the roots. So it is called drip system. It is the best technique for watering fruit plants, gardens and trees [Figure 1.5(b)]. Water is not wasted at all. It is a boon in regions where availability of water is poor.

Figure 1.5 (b) : Drip System

Figure shows a Drip irrigation is sometimes called trickle irrigation and involves dripping water onto the soil at very low rates (2-20 litres/hour) from a system of small diameter plastic pipes fitted with outlets called emitters or drippers.