Irrigation, the artificial application of water to soil to produce plant growth. In the broadest sense, irrigation includes watering a lawn or garden. However, the term usually means the supplying of rather large amounts of water to grow crops in arid (dry) regions.
Under extremely arid conditions, irrigation takes the place of rainfall. In regions where rainfall is scant, irrigation may provide an alternative to dry farming. Where rainfall is abundant but uncertain, irrigation gives protection against occasional droughts. Under all circumstances, irrigation is a method of producing crops on a controlled schedule of cultivation and harvest.
Any crop may be grown with irrigation. Lowland rice—the leading source of food for about half of the world's population—is grown on land flooded with water. Sugar beets, alfalfa, and various fruits are typical irrigated crops in the western United States.
The world's rapid population growth has greatly increased the need for food. Irrigation is therefore important as a means of opening new lands to agriculture. Also, higher crop yields are possible on old lands when irrigation is carried on scientifically.
Irrigation is used throughout the world. It is most common in regions having less than 20 inches (500 mm) of rainfall a year. Irrigation also is practiced to some extent in regions where rainfall is 20 to 40 inches (500 to 1,000 mm) a year. Most of the irrigated land in the United States is in the West.
