IRRIGATION AND DRAINAGE

artificial application of water to land and artificial removal of excess water from land, respectively. Some land requires irrigation or drainage before it is possible to use it for any agricultural production; other land profits from either practice to increase production. Some land, of course, does not need either. Although either practice may be, and both often are, used for nonagricultural purposes to improve the environment, this article is limited to their application to agriculture. Irrigation and drainage improvements are not necessarily mutually exclusive. Often both may be required together to assure sustained, high-level production of crops. Additional reading K.K. Framji, B.C. Garg, and S.D.L. Luthra, Irrigation and Drainage in the World, 3rd ed., rev. and enlarged, 3 vol. (1981-83), outlines the development of irrigation in various countries of the world and describes major projects. B.A. Stewart and D.R. Nielsen (eds.), Irrigation of Agricultural Crops (1990), considers both theoretical and practical aspects. Glenn J. Hoffman, Terry A. Howell, and Kenneth H. Solomon (eds.), Management of Farm Irrigation Systems (1990), is a practical handbook. Glenn O. Schwab et al., Soil and Water Conservation Engineering, 4th ed. (1993), is also instructive. The Editors of the Encyclopdia Britannica