Irrigation, artificial application of water to soil to promote plant growth. Irrigation is vital for agricultural land with inadequate rainfall. The practice dates back at least to the canals and reservoirs of ancient Egypt. There are 3 main irrigation techniques: surface irrigation, in which the soil surface is moistened or flooded by water flowing through furrows or tubes; sprinkler irrigation, in which water is sprayed on the land from above; and subirrigation, in which underground pipes supply water to roots.
See also: Agriculture.