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Drip irrigation is based on the constant application of a specific and focused quantity of water to soil crops. The system uses pipes, valves and small drippers or emitters transporting water from the sources (i.e. wells, tanks and or reservoirs) to the root area and applying it under particular quantity and pressure specifications. The system should maintain adequate levels of soil moisture in the rooting areas, fostering the best use of available nutrients and a suitable environment for healthy plant roots systems. Managing the exact (or almost) moisture requirement for each plant, the system significantly reduces water wastage and promotes efficient use. Compared to surface irrigation, which can provide 60 per cent water-use efficiency and sprinklers systems which can provide 75 per cent efficiency, drip irrigation can provide as much as 90 per cent water-use efficiency (FAO, 2002).
In recent times, drip irrigation technology has received particular attention from farmers, as water needs for agricultural uses have increased and available resources have diminished. In particular, drip irrigation has been applied in arid and semi-arid zones as well as in areas with irregular flows of water (or in zones with underground water resources that rely on seasonal patterns such as river-flow or rainfall).
Figure 1: Drip irrigation system for an Olives tree farm in Ica Valley, Peru (Source: Courtesy of Rafael Garvan, Farm Manager Agriver SAC (2001))
Description:
A drip irrigation system typically consists of:
- Pumps or pressurised water system
- Filtration systems
- Nutrients application system
- Backwash Controller
- Pressure Control Valve (Pressure Regulator)
- Pipes (including main pipe line and tubes)
- Control Valves and Safety Valves
- Poly fittings and Accessories (to make connections)
- Emitters
A wide range of components and system design options is available. Drip tape varies greatly in its specifications, depending on the manufacturer and its use. The wetting pattern of water in the soil from the drip irrigation tape must reach plant roots. Emitter spacing depends on the crop root system and soil properties.
Drip irrigation zones can be identified based on factors such as topography, field length, soil texture, optimal tape run length, and filter capacity. Many irrigation system suppliers use computer programs to analyse these factors and design drip systems. Once the zones are assigned and the drip system is designed, it is possible to schedule irrigations to meet the unique needs of the crop in each zone. Recent automatic systems technology has been particularly useful to help control flows and pressure, and to identify potential leaks thereby reducing labor requirements. System design must take into account the effect of the land topography on water pressure and flow requirements. A plan for water distribution uniformity should be made by carefully considering the tape, irrigation lengths, topography, and the need for periodic flushing of the tape. The design should also include vacuum relief valves into the system. Figure 2 shows a drip irrigation system for capers filed in Peru.
Figure 2: Capers field under Drip Irrigation system in Sandy Soil Pisco Valley Peru (Source: Courtesy of Rafael Garvan, Farm Manager Agriver SAC (2001))
Drip irrigation technology can support farmers to adapt to climate change by providing efficient use of water supply. Particularly in areas subject to climate change impacts such as seasonal droughts, drip irrigation reduces demand for water and reduces water evaporation losses (as evaporation increases at higher temperatures). Scheduled water application will provide the necessary water resources direct to the plant when required. Furthermore, fertiliser application is more efficient since it can be applied directly through the pipes.
As is the case with a sprinkler system, drip irrigation is more appropriate where there is (or is expected to be) limited or irregular water supply for agricultural use. However, the drip technology uses even less water than sprinkler irrigation, since water can applied directly to the crops according to plant requirements. Furthermore, the drip system is not affected by wind or rain (as is the sprinkler technology).
Drip irrigation can help use water efficiently. A well-designed drip irrigation system reduces water run-off through deep percolation or evaporation to almost zero. If water consumption is reduced, production costs are lowered. Also, conditions may be less favorable for the onset of diseases including fungus. Irrigation scheduling can be managed precisely to meet crop demands, holding the promise of increased yield and quality.
Agricultural chemicals can be applied more efficiently and precisely with drip irrigation. Since only the crop root zone is irrigated, nitrogen that is already in the soil is less subject to leaching losses. In the case of insecticides, fewer products might be needed. Fertiliser costs and nitrate losses can be reduced. Nutrient applications can be better timed to meet plants' needs.
The drip system technology is adaptable to terrains where other systems cannot work well due to climatic or soil conditions. Drip irrigation technology can be adapted to lands with different topographies and crops growing in a wide range of soil characteristics (including salty soils). It has been particularly efficient in sandy areas with permanent crops such as citric, olives, apples and vegetables.
A drip irrigation system can be automated to reduce the requirement for labour.
The initial cost of drip irrigation systems can be higher than other systems. Final costs will depend on terrain characteristics, soil structure, crops and water source. Higher costs are generally associated with the costs of pumps, pipes, tubes, emitters and installation. Unexpected rainfall can affect drip systems either by flooding emitters, moving pipes, or affecting the flow of soil salt-content. Drip systems are also exposed to damage by rodents or other animals. It can be difficult to combine drip irrigation with mechanised production as tractors and other farm machinery can damage pipes, tubes or emitters.
The technology is widely variable, however the cost of a drip irrigation system ranges from US$ 800 to US$ 2,500 per hectare depending on the specific type of technology, automatic devices, and materials used as well as the amount of labor required. Financing for equipment may be available from financial institutions via leasing operations or direct credit. Farmers usually cover installation, design and training costs that represent about 30 to 40 per cent of final costs depending on the size of the land, characteristics and shape, crops, and particular technology applied.
Investment will also be required to build workers capacities in order to accurately manage maintenance and water flow control. For example, drip tape or tubing must be carefully maintained in order to avoid leaking or plugging and emitters must be regularly cleaned to avoid blockage from chemical deposits. In certain cases, it would be necessary to redesign the farm weed control programme.
Drip irrigation is particularly suitable for use with ground water from wells. It requires institutional arrangements and capacity building of water users to avoid an overuse of aquifer resources and potential conflicts. Drip irrigation technologies can be implemented via a water user association to improve economic benefits and reduce initial investment costs. Drip irrigation is a versatile technology suitable for application in a wide range of contexts. It can be implemented at small or large scales and with low-cost or more sophisticated components. This technology can be employed in conjunction with other adaptation measures such as the establishment of water user boards, multi-cropping and fertiliser management. Promoting drip irrigation contributes to efficient water use, reduces requirements for fertilisers and increases soil productivity. It is particularly suitable in areas with permanent or seasonal water scarcity, since crop varieties to plant can also be adaptable to these conditions.
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