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Sprinkler irrigation is a method of providing rainfall-like irrigation to the crops. Water is distributed through a system of pipes usually by pumping. Spray heads at the outlets distribute the water over the entire soil surface.
Region-wise spread of sprinkler irrigated area in 2006 was
- Americas 13.3 Mio. ha
- Europe 10.1 Mio. ha
- Asia 6.8 Mio ha
- Africa 1.9 Mio. ha
- Oceania 0.9 Mio. ha
The top ten sprinkler irrigated countries were USA, Russia, China, India, France, Brazil, Italy, Spain, Saudi Arabia and Ukraine. These countries together constituted 75% of total sprinkler-irrigated area.
A typical sprinkler irrigation system consists of the following components:
- Pump unit;
- Mainline (and sometimes sub-mainlines);
- Lateral lines;
The pump unit is usually a centrifugal pump, which takes water from the source and provides adequate pressure for delivery into the pipe system.
Mainline and sub-mainline pipes deliver water from the pump to lateral pipes. In some cases these pipelines are permanent and are laid on the soil surface or buried below ground. In other cases they are temporary, and can be moved from field to field.
There are different types of sprinkler heads in use, depending on the actual irrigation purpose and plot sizes:
Types of Sprinkler Heads
Rotor-type sprinklers operate by rotating streams of water over the surface. They include impact and gear-drive sprinklers producing moving streams of water and spray nozzles that discharge water on the whole wetted pattern at all times. Impact or gear-drive sprinklers can accommodate only full or part circle application patterns. Since each sprinkler covers a large area (typically 12 m head-to-head spacing), they are used on larger plot sizes.
An impact sprinkler is mounted on a bearing that allows the entire sprinkler body to spin in circles. It is rotated by the impact of a swinging arm repeatedly striking the body of the sprinkler, causing it to rotate slightly each time. Cam drive or ball drive sprinklers also impact sprinklers, however the impact is caused by either a cam or a ball bearing inside the body of the sprinkler. With ball and cam drive rotors only the nozzle moves. Ball and cam drive sprinklers are no longer present on the market, but may be still in use.
As impact sprinklers tend not to rotate in a uniform manner, they are replaced by gear-driven rotors on the market. As with cam and ball drives, only the nozzle on a gear-driven sprinkler head moves. The water moving through the sprinkler spins a turbine, which turns a set of gears, which again turn the nozzle. These gear-drive rotors have one or more streams of water rotating. In agricultural irrigation, these sprinklers are usually in operation on very large plot sizes. They require a higher input pressure.
Centre pivot irrigation is a form of overhead sprinkler irrigation consisting of several segments of pipe mounted on wheeled towers with sprinklers positioned along its length. The usually self-propelled structure moves in a circular pattern and is fed with water from the pivot point at the centre of the circle. The amount of water applied is controlled by the speed of rotation. Centre pivots can be adjusted to any crop height and are particularly suited for lighter soils. With a computerized control system, the operator is able to program many features for the irrigation process. Furthermore, it is possible to install a corner attachment system (also called “end-gun”) which allows irrigation of corner areas missed out by conventional centre pivot systems.
A linear move (also called lateral move) irrigation system is built the same way as a centre pivot; the main difference is that all the towers move at the same speed and in the same direction. Water is pumped into one of the ends or into the centre.
A travelling big gun system uses a large-capacity nozzle and high pressure to throw water out over the crop as it is pulled through an alley in the field. Travelling big guns come in two main configurations: hard-hose or flexible-hose feed. With the hard-hose system, a hard polyethylene hose is wrapped on a reel mounted on a trailer. The trailer is anchored at the end or centre of the field. The gun is connected to the end of the hose and is pulled towards the trailer. The gun is pulled across the field by the hose winding up on the reel. With the flexiblehose system, the gun is mounted on a four-wheel cart. Water is supplied to the gun by a flexible hose from the main line. A cable winch pulls the cart through the field towards the cart.
A side roll (also called wheel roll) system consists of long lateral pipes mounted on 1 to 3 meter wheels in diameter and the pipe serving as an axle. When the desired amount of water has been applied to an area, a gasoline engine at the centre is used to move the side roll to the next. The sprinklers are generally mounted on weighted, swiveling connectors so that no matter where the side roll is stopped, the sprinklers will always be on top.
Due to the high capital investment, centre pivots, linear moves, travelling big guns and side roll systems are used on high-value crops such as potatoes and vegetables. A higher level of expert knowledge is necessary to carry out irrigation with these systems, even though the labor requirement is relatively low due to the automation. Motors, water supply pipes/hoses and all mechanical components have to be maintained systematically to avoid damage and high repair costs. Sprinklers provide efficient coverage for small to large areas. Sprinkler irrigation is suited for most row, field and tree crops and water can be sprayed over or under the crop canopy. However, large sprinklers are not recommended for irrigation of delicate crops such as lettuce because the large water drops produced by the sprinklers may damage the crop.
Advantages and Disadvantages
Advantages of sprinkler irrigation systems include:
- Expansive land leveling or terracing is not required;
- No loss of cultivable area due to channel construction;
- Suitable for almost all soil types;
- Water saving irrigation intensity can be changed in accordance with the infiltration capacity of soil and crop water requirements;
- High efficiency due to uniform water distribution, crop water management can be adapted to growth stage and conditions;
- Possibility of adding fertilizers or pesticides to irrigation water in an economic way;
- Possibility of irrigating for other purposes: sprouting, frost protection or cooling during hot periods;
- Lower labor requirements as compared to traditional surface irrigation approaches.
Disadvantages of sprinkler irrigation include:
- High initial capital costs (investment in equipment - sprinklers and pipes) and high operation costs due to energy requirements for pumping and labor costs.
- Sensitivity to wind, causing evaporation losses (under high wind condition and high temperature distribution and application efficiency is poor);
- Unavoidable wetting of foliage in field crops results in increased sensitivity to diseases;
- Highly saline water (>7 millimhos/cm) causes leaf burning when temperature higher than 35 degrees (Celsius).
- Debris and sediments in irrigation water can cause clogging of sprinkler nozzles.
Sprinkler irrigation is adaptable to any farmable slope, whether uniform or undulating. The lateral pipes supplying water to the sprinklers should always be laid out along the land contour whenever possible to minimize the pressure changes at the sprinklers and provide a uniform irrigation. A good clean supply of water, free of suspended sediments, is required to avoid problems of sprinkler nozzle blockage and spoiling the crop by coating it with sediment. The pump supply system, sprinklers and operating conditions must be designed to enable a uniform application of water. Sprinkler irrigation can also be adapted to nearly all irrigable soils since sprinklers are available with a variety of discharge capacities. However, sprinklers are best suited to sandy soils with high infiltration rates. The average application rate from the sprinklers (in mm/hour) is always chosen to be less than the basic infiltration rate of the soil so that inundation/flooding and runoff can be avoided. Sprinklers are not suitable for soils which easily form a crust.
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