Class 8 Science


Table of Contents

Plants need plenty of water to grow. Farmers need to supply water to crops at regular intervals. This practice is called irrigation. Different types of crop require different amount and frequency of irrigation. Kharif crops need more water than rabi crops.

Sources of Irrigation: Wells, tube-wells, ponds, lakes, rivers, canals, etc.

Traditional Methods of Irrigation

In traditional method, human or animal labour is used.

Moat (Pulley System)

This is composed of a pulley and a rope. A bucket is tied to one end of rope. Another end of rope is pulled through over the pulley in order to draw water.

Chain Pump

Chain pump is composed of a wheel which is turned with the help of a chain. Many circular discs are fitted along with the chain. Movement of discs along with the chain helps in drawing water.


Dhekli is composed of a long wooden beam which turns around a lever. A bucket is fitted at the longer end of the beam. The shorter end is pressed and raised by foot to fill and lift water.


Rahat is also called Persian Wheel because it came from Persia. Rahat is composed of a big wheel with buckets fitted on the rim. Rahat is turned with the help of cattle; which helps in drawing water from a reservoir.

Manual pumps are now being replaced by motor-driven pumps. Such motors are powered either by electricity or by diesel engine.

Modern Methods of Irrigation

Sprinkler System

The sprinkler system is composed of a series of pipelines. Vertical sprinklers are fitted at suitable gaps on the pipes. Water is pushed through the pipes with the help of a pump. The nozzle of the sprinkler keeps on rotating. It results in a jet of water being sprinkled on plants. Sprinkler system is ideal for irrigation on uneven land.

Drip Irrigation

In this system, pipes are laid near the base and along the queue of plants. The pipes have small holes at frequent gaps. The holes facilitate gradual dripping of water on the base of plants. This method is ideal for areas which are suffering from shortage of water.

Importance of Irrigation

Protection from Weeds

Weeds: Any unwanted plant which grows along with crops is called weed. While some weeds are poisonous, many are not harmful. However, weeds compete with plants for various resources; like sunlight, air, water and nutrients. Weeds hamper the normal growth of plants. Hence, removal of weeds is necessary for a good harvest.

Weeding: Removal of weeds is called weeding. Weeding is usually done manually or by using a trowel. Weeds are also removed during ploughing. Weedicides are the chemicals which destroy weeds. 2, 4 – D is an example of weedicide. Weedicides are sprayed before flowering and seeding in weeds. A farmer needs to take precautions to prevent any harm from weedicide. The farmer needs to wear protective cloths and masks while spraying a weedicide.


Harvesting involves cutting the mature crop. Traditionally, harvesting is done manually by using sickles. Combine harvesters are used on large farms. A combine harvester does harvesting and threshing at one go.

Threshing: Separation of grains from harvested crop is called threshing. Threshing is done by threshing machine or by cattle.

Winnowing: Separation of grains and chaff is called winnowing. Winnowing is done manually or by machines.


Proper storage of harvested crop is necessary to prevent damage from moisture and pests. Grains are generally dries in the sun before being stored. Silos of different sizes are used for storing grains. Fruits and vegetables and other perishable items are stored in cold storage. Pesticides are also used while storing grains.

Food from Animals

Animals are important source of food for us. Many animals are reared for milk. Some animals are reared for meat, e.g. goats and poultry. Fish is an important source of meat. Honey is obtained from honeybees.

Animal Husbandry: Animal husbandry involves rearing of animals for food and other products.

Methods of Irrigation