1. Irrigation
Source: USDA - Natural Resources Conservation Service
Irrigation makes agriculture possible in areas previously unsuitable for intensive crop
production. Irrigation transports water to crops to increase yield, keep crops cool under
excessive heat conditions and prevent freezing.
Less than 15% of U.S. cropland is irrigated, although irrigation is essential for crop
production in some of the most productive areas of the country. For instance, in
Arizona, home to some the highest corn yields in the country (208 bushel per acre state
average in 2001 compared to 152 for Illinois), much of the crop is under continuous
irrigation from planting until harvest.
The need to irrigate is usually driven by the necessity to meet the water needs of the
crop from year to year (some areas of the country simply receive too little rainfall
during the growing season to support economical crop growth). In other situations,
irrigation is viewed as insurance against occasional drought. In areas where rainfall is
plentiful in most years, irrigation can bring benefits by reducing risk, meaning that a
farmer 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

2. In 1997 there were about 55 million irrigated crop acres in the U.S. Irrigation is
concentrated in certain areas like central California, Nebraska and the Great Plains, and
the lower Mississippi valley.
Although irrigation has always been most common in the West, U.S. irrigated acreage
in the East has also grown from 11 percent of acres in 1969 to 22 percent of acres in
1997.
Irrigation water is obtained from either ground water or surface water. Wells drilled on
the farm are a common source of water in many areas, and are usually the only source
used in the Great Plains. Offsite sources such as rivers, pipelines, canals operated by
irrigation 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.

3. Equipment Used
There are four primary types of irrigation:
Surface irrigation,
Sprinkler irrigation,
Drip or trickle irrigation, and
Subsurface irrigation (or "subirrigation").
Source: USDA - Natural Resources Conservation Service
Surface Irrigation - With surface irrigation, water flows directly over the surface of the
soil. 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 row
crops).

4. Center Pivot Irrigation
Source: USDA - Natural Resources Conservation Service
Sprinkler Irrigation - With sprinkler irrigation, water is sprayed through the air from
pressurized nozzles, and falls like rain on the crop.
Source: USDA - Natural Resources Conservation Service
Variable-Flow Irrigation - Variable-flow irrigation sprinkler head improves the
precision of water and farm chemical applications.

5. Source: USDA - Natural Resources Conservation Service
Trickle or Drip Irrigation - Trickle or drip irrigation supplies water directly onto or
below the soil surface through "emitters' that control water flow.
Source: Modified from graphic by Leslie Zucker, Ohio State University Extension
Subirrigation - With subirrigation, the water table is artificially raised either through
blocking ditches or by supplying water through the perforated pipes also used for
subsurface drainage.
Irrigation types can be further distinguished by whether the equipment is permanently
installed in one place (stationary system) or whether it is used until the necessary
amount of water is applied, then moved to a different area (traveling system). Stationary
systems such as permanent spray installations or trickle systems require less labor, but
usually cost much more to install. Traveling systems such as center pivot sprinkler
irrigation, linear-move, or cable-tow require more labor but less capital expense.