Irrigation by canals is more suitable in Northern India because

1. it is cheap
2. it irrigates larger area
3. the surface of the northern plain is flat with soft soil
4. it is perennial

Canal irrigation leads to the ground around it becoming unproductive because

1. due to waterlogging the capacity of the soil to absorb water decreases and the water which collects can ruin the crop
2. percolation of water through canal can lead to swamps
3. problem of salt effervescence due to over-flooding of the fields make the soil unsuitable for farming
4. all the above

Connect the correct pairs.

What is irrigation?