Irrigation Source: USDA - Natural Resources Conservation ServiceIrrigation makes agriculture possible in areas previously unsuitable for intensive cropproduction. Irrigation transports water to crops to increase yield, keep crops cool underexcessive heat conditions and prevent freezing.Less than 15% of U.S. cropland is irrigated, although irrigation is essential for cropproduction in some of the most productive areas of the country. For instance, inArizona, home to some the highest corn yields in the country (208 bushel per acre stateaverage in 2001 compared to 152 for Illinois), much of the crop is under continuousirrigation from planting until harvest.The need to irrigate is usually driven by the necessity to meet the water needs of thecrop from year to year (some areas of the country simply receive too little rainfallduring the growing season to support economical crop growth). In other situations,irrigation is viewed as insurance against occasional drought. In areas where rainfall isplentiful in most years, irrigation can bring benefits by reducing risk, meaning that afarmer is better able to control income fluctuation. Other benefits include: Improving crop quality (most noticeable for vegetable crops) Significantly increasing crop yields, particularly on sandy soils which have low moisture-holding capacities Increasing opportunities for double cropping (planting soybeans after wheat in the same year) Providing a means of liquid fertilizer application
In 1997 there were about 55 million irrigated crop acres in the U.S. Irrigation isconcentrated in certain areas like central California, Nebraska and the Great Plains, andthe lower Mississippi valley.Although irrigation has always been most common in the West, U.S. irrigated acreagein the East has also grown from 11 percent of acres in 1969 to 22 percent of acres in1997.Irrigation water is obtained from either ground water or surface water. Wells drilled onthe farm are a common source of water in many areas, and are usually the only sourceused in the Great Plains. Offsite sources such as rivers, pipelines, canals operated byirrigation districts and private water companies, are also used, mainly in western states.The percentage of water source used for irrigation varies across the U.S.
Equipment UsedThere are four primary types of irrigation: Surface irrigation, Sprinkler irrigation, Drip or trickle irrigation, and Subsurface irrigation (or "subirrigation"). Source: USDA - Natural Resources Conservation ServiceSurface Irrigation - With surface irrigation, water flows directly over the surface of thesoil. The entire surface can be flooded (most often used for crops that are sown, drilled,or seeded) or the water can be applied through furrows between the rows (for rowcrops).
Center Pivot Irrigation Source: USDA - Natural Resources Conservation ServiceSprinkler Irrigation - With sprinkler irrigation, water is sprayed through the air frompressurized nozzles, and falls like rain on the crop. Source: USDA - Natural Resources Conservation ServiceVariable-Flow Irrigation - Variable-flow irrigation sprinkler head improves theprecision of water and farm chemical applications.
Source: USDA - Natural Resources Conservation ServiceTrickle or Drip Irrigation - Trickle or drip irrigation supplies water directly onto orbelow the soil surface through "emitters that control water flow.Source: Modified from graphic by Leslie Zucker, Ohio State University ExtensionSubirrigation - With subirrigation, the water table is artificially raised either throughblocking ditches or by supplying water through the perforated pipes also used forsubsurface drainage.Irrigation types can be further distinguished by whether the equipment is permanentlyinstalled in one place (stationary system) or whether it is used until the necessaryamount of water is applied, then moved to a different area (traveling system). Stationarysystems such as permanent spray installations or trickle systems require less labor, butusually cost much more to install. Traveling systems such as center pivot sprinklerirrigation, linear-move, or cable-tow require more labor but less capital expense.