Irrigation is the the controlled application of water for agricultural purposes through man made systems to supply water requirements not satisfied by rainfall. Crop irrigation is vital throughout the world in order to provide the world's ever-growing populations with enough food. Irrigation is the act of artificially applying water to soil to allow plant growth. This can also include applying water to a lawn or garden. The term usually refers to providing large amounts of water in arid or dry regions to grow crops. The world's rapid population growth has produced more of a need for irrigation. With it, a higher crop yield is possible on older lands.
Although irrigation is most commonly used in areas with up to 20 inches (500 mm) of rainfall annually, sometimes it also is practiced in areas where the annual rainfall is 20 to 40 inches (500 to 1,000 mm). Irrigation helps to protect against droughts where rainfall is plentiful but uncertain. And in many circumstances, irrigation is applied to grow crops on a set schedule of cultivation and harvest. This type of irrigation also is applied to crops as flood irrigation -- water pumps or is brought to the fields along the ground to flood the crops. It is not an efficient watering method [source: United States Geological Survey].
Water Use
The amount of water that is to be used for irrigation depends on the type of crop that is being farmed as well as the amount of rainfall in the region. There are some countries where water is used for irrigating land more than it is used for other purposes. In the US, about one-third of the water that is utilized each year is used for irrigation. Worldwide, it is more than half.
Water Sources
Water that is brought to a farm from a source of surface water, such as a lake or reservoir, usually is done so through a series of canals. In some places, snowfall and rainfall are the main suppliers of irrigation water, but in other locales, groundwater is essential. Surface water used for irrigation is stored naturally in lakes and ponds and is conveyed by rivers and streams. Groundwater collects in basins of coarse gravel and in aquifers, which are water-bearing rocks. It reaches the surface through springs. The natural sources discharge mainly in the spring and dry up in summer. Because of that natural cycle, artificial surface reservoirs are increasingly being used to store irrigation water. The largest are dams. Water also can be obtained from wells, where water from storm-filled streams is directed and collected in the ground to fill underground basins.Some irrigation methods
Many different irrigation methods are used worldwide, including:- Center-Pivot: Automated sprinkler irrigation achieved by automatically rotating the sprinkler pipe or boom, supplying water to the sprinkler heads or nozzles, as a radius from the center of the field to be irrigated. Water is delivered to the center or pivot point of the system. The pipe is supported above the crop by towers at fixed spacings and propelled by pneumatic, mechanical, hydraulic, or electric power on wheels or skids in fixed circular paths at uniform angular speeds. Water is applied at a uniform rate by progressive increase of nozzle size from the pivot to the end of the line. 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.
- Drip: A planned irrigation system in which water is applied directly to the Root Zone of plants by means of applicators (orifices, emitters, porous tubing, perforated pipe, etc.) operated under low pressure with the applicators being placed either on or below the surface of the ground.
- Flood: The application of irrigation water where the entire surface of the soil is covered by ponded water.
- Furrow: A partial surface flooding method of irrigation normally used with clean-tilled crops where water is applied in furrows or rows of sufficient capacity to contain the designed irrigation system.
- Gravity: Irrigation in which the water is not pumped but flows and is distributed by gravity.
- Rotation: A system by which irrigators receive an allotted quantity of water, not a continuous rate, but at stated intervals.
- Sprinkler: A planned irrigation system in which water is applied by means of perforated pipes or nozzles operated under pressure so as to form a spray pattern.
- Subirrigation: Applying irrigation water below the ground surface either by raising the water table within or near the root zone or by using a buried perforated or porous pipe system that discharges directly into the root zone.
- Traveling Gun: Sprinkler irrigation system consisting of a single large nozzle that rotates and is self-propelled. The name refers to the fact that the base is on wheels and can be moved by the irrigator or affixed to a guide wire.
- Supplemental: Irrigation to ensure increased crop production in areas where rainfall normally supplies most of the moisture needed.
- Surface: Irrigation where the soil surface is used as a conduit, as in furrow and border irrigation as opposed to sprinkler irrigation or subirrigation.
This information is courtesy of the Nevada Division of Water Planning, wisegeek, United States Geological survey
