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This bar chart gives you an idea of what kinds of crops need and receive irrigation. The bars show the percent of farmland by crop type that is irrigated. For example, 100-percent of the land used to grow rice is irrigated. But only about 35 percent of the land used to grow cotton is irrigated. The other 65 percent depends on rainfall.

Look at some of the numbers and try to figure out why some crops need irrigating and some don't. Rice actually grows underwater in flooded fields. It's no wonder that all riceland is irrigated. Other crops are grown in the South where there is normally ample rainfall during the growing season. Other crops, such as corn, don't rely on irrigation. Maybe it is because it is grown in huge amounts in the Midwest, where it would cost too much to pump the needed ground water.

Source: Day, J.C., and Horner, G.L. 1987, U.S. Irrigation, Extent and Economic Importance,
U.S. Dept. of Agriculture Information Bulletin 532

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Irrigation water use | Irrigation techniques | Irrigation methods
Irrigation use, 2000: Data table | Map
Charts:By crop type | Irrigated land
Irrigation methods: Spray | Flood | Drip | Low-energy