Evaluating Irrigation Efficiency

Irrigated agriculture is and has been the largest user of fresh water, but it also has been accused of being an inefficient and uneconomical user. A major part of the water used by irrigated agriculture is vaporized (evapotranspiration), in contrast to other uses that do not "consume" water. Evapotranspiration is largely controlled by meteorological conditions when adequate water is provided, and a full crop canopy exists. Significant reductions in evapotranspiration, without corresponding yield reductions, on the bulk of the 44,000,000 acres of irrigated land in the United States is possible, but is not economically feasible now (in 1967), or in the near future. In contrast, significant reductions in canal seepage, deep percolation, runoff, and operational wastes may be economically feasible now. The agricultural industry has, during the past two decades, increased its efficiency of producing food and fiber per unit of water vaporized by using better crop varieties, insect control, improved irrigation and agronomic practices, and inorganic fertilizers. Further increases are possible and are being developed through research, but additional increases are not expected to be proportionally as great as those that have occurred during the past quarter century (since the 1940's)