IRRIGATION (Lat. irrigatio, from irrigate, to irrigate, from in, in rigarc, to moisten: con. neeted with Goth. rigs, AS. neon, 01T(1. regan, Ger. Prgen. Eng. ruin, and probably with Gk. pptrEtv, breehcin. to wet). In agriculture, the method of increasing the productiveness of soils by an artificial supply of water. The practice of irrigation is very ancient. There is evidence to show that works for the storage and distribution of irrigation water were constructed in Egypt as early as B.C. 2000. Extensive works, intended for irrigation on a large scare, existed in times of remote antiquity also in Assyria, MesopW tamia, Persia, India, Ceylon, China, and other parts of the earth, as well as in Peru and ..11exieo in the Western Hemisphere. Remains of ancient irrigation works are found in the Southwestern United States (New Mexico and Arizona). In all of these regions irrigation is necessary for successful agriculture, because the rainfall is insufficient for the needs of ordinary crops. Irrigation is also required even in humid regions for crops, such as rice and cranberries, which require a large amount of water.
The area of the earth's surface over Nvh ieh the rainfall is deficient (less than 20 inches or 500 millimeters), and irrigation consequent ly a necessity for successful agriculture, i; very extensive. In addition to this vast area in which, as a rule, agriculture is impossible without irrigation, there are considerable areas in the so-called humid regions in which the irregularity of the rainfall makes irrigation profitable. The extent to which the *arid lands
can be reclaimed depend; upon the water-sup ply available for irrigation. It has been es timated that there is sufficient water to irrigate only about one-tifth of the arid region of the United States, or from 150.000.000 to 200. 000,000 acres. Of this irrigable area probably less than 10.000,000 acres have already been re claimed. In Europe irrigation prevails chiefly in the south, where it was introduced by the, Romans. It is most extensively and systemati cally practiced in Lombardy. Spain, and the south of France, but exists to some extent in other parts of Europe. Wilson estimates the irrigated area in Italy to be about 3,070.000 acres, in Spain 5(10.1100 acres, in France 400.000 acres. No where is irrigation practiced on so large a scale as in India, and the irrigation systems of that country are being rapidly extended by the Brit ish Government. According to Wilson, the irri gated area in India is about 25.000,000 acres. Egypt follows with 6,000.000 acres, although ir rigation works now in process of construction will vastly increase this area. Only at a com paratively recent date has irrigation been in troduced into Australia, but it i; rapidly extend ing there. The same is true in a measure of South Africa. The practice of irrigation has dcelined. or entirely disappeared, in many of those regions where it prevailed most extensively in remote antiquity.