Define irrigation. Why is irrigation of crops essential? Mention the harmful effects of excessive irrigation.

Irrigation is the process of supplying water to crop plants by means of canals, wells, reservoirs, tube-wells, etc.

Irrigation is necessary in the areas where there is scarcity and irregular distribution of rain causing conditions like drought. It provides sufficient moisture for the germination of seeds, as seeds do not germinate in dry soil. It is also necessary for the growth and development of crop plants. The irrigation water tends to dissolve the nutrients present in the soil and forms a solution which is easily absorbed by the roots of the plants and helps in its growth.

Excessive irrigation causes water logging and increases surface salinity. In waterlogged soil, plants do not get proper aeration and die due to lack of air.