System of supplying land with water by artificial means that transformed the American landscape and brought agriculture to areas previously unable to sustain it.
Fifty percent of the value of a farmer’s crop is in the lands he or she has under irrigation. Irrigation accounts for 80 percent of the nation’s consumptive water use and more than 90 percent in many western states. Although farmers have irrigated fields for more that 4,000 years, they did not use irrigation on a massive scale in the United States until the 1950s. In 1946, 250,000 acres received water from sprinkler irrigation in the United States, but by 1954, roughly 3 million acres received water by this method. Government sources estimate that 500,000 additional acres of land went under sprinkler irrigation each year throughout the 1950s. On the Great Plains, the center-pivot sprinkler had irrigated 400,000 acres by 1974, a fourfold increase since 1955. Other forms of irrigation had equally dramatic increases throughout the latter half of the twentieth century. Currently 10 million acres are under irrigation; 10 trillion gallons of water are used for irrigation annually. Sixty percent of the nation’s vegetables and 25 percent of the nation’s fruit and nut crops are irrigated.
Irrigation has allowed lands that were previously marginal or used for dryland wheat and grain sorghum to yield corn, sugar beets, alfalfa, and cotton. By 1954, the use of irrigation and fertilizer increased the per acre yield of crops such as alfalfa by 2.4 tons, forage sorghums by 9.5 tons, grain sorghum by 22 bushels, and wheat by 11 bushels. By 1990, tomatoes increased from 26 to 100 tons per acre and cotton jumped from 930 to 1,000 pounds per acre. These increases in yield brought greater farm income on the Great Plains and in the West. In Kansas alone, by 1966, irrigation had increased farm income by $24 million. This increased irrigation allowed farmers to expand their feedlots and develop a meatpacking industry on the Great Plains. In areas with little or sporadic rainfall, irrigation has led to a larger, more stable, agricultural industry and a cheaper food supply, although it has had environmental costs. One such area is Imperial Valley, California, where irrigation has yielded 115 million acres of annual vegetable production worth $350 million.
