Enhancing water use efficiency in irrigated agriculture

Irrigated agriculture is a vital component of total agriculture and supplie s many of the fruits, vegetables, and cereal foods consumed by humans; the grains fed to animals that are used as human food; and the feed to sustain animals for work in many parts of the world. Irrigation worldwide was pract iced on about 263 Mha in 1996, and about 49% of the world's irrigation occu rred in India, China, and the USA. The objectives of this paper are to (i) review irrigation worldwide in its ability to meet our growing needs for fo od production, (ii) review irrigation trends in the USA, (iii) discuss vari ous concepts that define water use efficiency (WUE) in irrigated agricultur e from both engineering and agronomic viewpoints, and (iv) discuss the impa cts of enhanced WUE on water conservation, Scarcely one-third of our rainfa ll, surface water, or ground water is used to produce plants that are usefu l to mankind. Without appropriate management, irrigated agriculture can be detrimental to the environment and endanger sustainability, Irrigated agric ulture is facing growing competition for low-cost, high-quality water. In i rrigated agriculture, WUE is broader in scope than most agronomic applicati ons and must be considered on a watershed, basin, irrigation district, or c atchment scale. The main pathways for enhancing WUE in irrigated agricultur e are to increase the output per unit of water (engineering and agronomic m anagement aspects), reduce losses of water to unusable sinks, reduce water degradation (environmental aspects), and reallocate water to higher priorit y uses (societal aspects).