The USGS Water Science School
Spray irrigation is a modern and commonly-used system of irrigating, but it also requires machinery. This system is similar to the way you might water your lawn at home - stand there with a hose and spray the water out in all directions. Large scale spray irrigation systems are in use on large farms today. The systems can simply be long hoses with sprinkers along the length or a center-pivot system that traverses a circle in the fields. This picture shows a simple sprinkler irrigation system—it is one of the less-efficient models because a large part of the water shot into the air evaporates.
This picture shows a very common center-pivot sprinkler irrigation system in operation. The center-pivot systems have a number of metal frames (on rolling wheels) that hold the water tube out into the fields. Electric motors move each frame in a big circle around the field (the tube is fixed at the water source at the center of the circle), squirting water. The depth of water applied is determined by the rate of travel of the system. Single units are ordinarily about 1,250 to 1,300 feet long and irrigate about a 130-acre circular area. In high-pressure systems, there can be very big water guns along the tube.
A more "modern" alternative to the high-pressure water guns is the low-pressure sprinker system, seen in the picture below. Here, water is gently sprayed downward onto plants instead of being shot high in the air. Low-pressure systems are more efficient in that much less water evaporates or is blown off the fields if there is a strong wind present.
Although still widely in use today, high-pressure spray irrigation system can be quite inefficient. A lot of water, up to 35 percent, is lost because of evaporation and the blowing winds. More efficient irrigation systems are being used more often.
Irrigation is one of the major uses of water throughout the world. In the United States in year 2000, irrigation withdrawals were an estimated 137,000 million gallons per day (Mgal/d), or 153,000 thousand acre-feet per year. About 61,900 thousand acres were irrigated in 2000. Of this total acreage, about 28,300 thousand acres with sprinkler systems. The average application rate was 2.48 acre-feet per acre for the United States.