ABSTRACT
Irrigation is the process of supplying supplemental water necessary for plant growth and development by several application techniques, e.g., microirrigation, surface irrigation, sprinkler irrigation, subirrigation (by raising a shallow water table), and subsurface irrigation. It is used not only in arid and semiarid areas of the world, but also in humid areas to supplement rainfall during periods of drought. In this context, water is applied after the crop has been planted and growth has begun. The depth and timing of the application are based on the crop water requirement, the irrigation water quality, the crop salt tolerance, and the available soil water storage capacity. These topics are discussed fully in other parts of the encyclopedia.
