Evaluating Irrigation Efficiency

Abstract

Irrigated agriculture is and has been the largest user of fresh water, but\nit also has been accused of being an inefficient and uneconomical user. A major\npart of the water used by irrigated agriculture is vaporized (evapotranspiration),\nin contrast to other uses that do not "consume" water. Evapotranspiration\nis largely controlled by meteorological conditions when adequate water is provided,\nand a full crop canopy exists. Significant reductions in evapotranspiration,\nwithout corresponding yield reductions, on the bulk of the 44,000,000 acres\nof irrigated land in the United States is possible, but is not economically\nfeasible now (in 1967), or in the near future. In contrast, significant reductions\nin canal seepage, deep percolation, runoff, and operational wastes may be\neconomically feasible now.\nThe agricultural industry has, during the past two decades, increased its\nefficiency of producing food and fiber per unit of water vaporized by using better\ncrop varieties, insect control, improved irrigation and agronomic practices,\nand inorganic fertilizers. Further increases are possible and are being\ndeveloped through research, but additional increases are not expected to be\nproportionally as great as those that have occurred during the past quarter\ncentury (since the 1940's).