drainage

drainage in agriculture, the removal of excess water from the soil, either by a system of surface ditches, or by underground conduits if required by soil conditions and land contour. Diesel or centrifugal pumps are sometimes used to drain large areas. Drainage was practiced in the Nile basin c.400 BC and in ancient Rome. Today drain pipes of clay, concrete, or plastic, laid several feet underground, are much used in the United States, where c.110 million farm acres (44.5 million hectares) were artificially drained in 1987. Proper drainage improves soil structure; increases efficiency of phosphorus fertilizer; conserves soil nitrogen; and controls waterlogging, leaching, and salinization of soils caused by irrigation .

drainage
1. The passage of water over and through the land surface, ultimately towards the sea. See DENDRITIC DRAINAGE; DERANGED DRAINAGE; DISCORDANT DRAINAGE; DRAINAGE DENSITY; DRAINAGE PATTERN; INCONSEQUENT DRAINAGE; and SUPERIMPOSED DRAINAGE.

2. Process of removing the gravitational water from soil, using artificial or natural conditions, such that freely moving water can drain, under gravity, through or off soil. See MOLE DRAIN; and TILE DRAIN.

drainage
1. The passage of water over and through the land surface, ultimately towards the sea. See dendritic drainage; deranged drainage; discordant drainage; drainage density; drainage pattern; inconsequent drainage; and superimposed drainage.

2. The process of removing the gravitational water from soil, using artificial or natural conditions, such that freely moving water can drain, under gravity, through or off soil. See mole drain and tile drain.