Systems of pressurised irrigation, sprinkler or drip, can improve water efficiency and contribute substantially to improved food production. Sprinkler irrigation is a type of pressurised irrigation that consists of applying water to the soil surface using mechanical and hydraulic devices that simulate natural rainfall (see Figure 1). These devices replenish the water consumed by crops or provide water required for softening the soil to make it workable for agricultural activities. The goal of irrigation is to supply each plant with just the right amount of water it needs. Sprinkler irrigation is a method by which water is distributed from overhead by high-pressure sprinklers, sprays or guns mounted on risers or moving platforms. Today a variety of sprinkler systems ranging from simple hand-move to large self-propelled systems are used worldwide. Global use of sprinkler irrigation is: the Americas (13.3 million hectares (Mha)), Europe (10.1 Mha), Asia (6.8 Mha), Africa (1.9 Mha), and Oceania (0.9 Mha) (Kulkarni et al, 2006).
A sprinkler irrigation system typically consists of:
i) A pump unit which takes water from the source and provides pressure for delivery into the pipe system. The pump must be set to supply water at an adequate pressure so that the water is applied at rate and volume adequate to the crop and soil types
ii) Main pipes and secondary pipes which deliver water from the pump to the laterals. In some cases these pipelines are permanently installed on the soil surface or buried below ground. In other cases they are temporary, and can be moved from field to field. The main pipe materials used include asbestos cement, plastic or aluminium alloy
iii) The laterals deliver water from the pipes to the sprinklers. They can be permanent but more often they are portable and made of aluminium alloy or plastic so that they can be moved easily
iv) Sprinklers, water-emitting devices which convert the water jet into droplets. The distribution of sprinklers should be arranged so as to wet the soil surface in the plot as evenly as possible.
A wide range of sprinkler systems is available for small and large-scale application. Set systems operate with sprinklers in a fixed position. These sprinklers can be moved to water different areas of the field, either by hand or with machinery. Hand-move systems are more labour intensive and may be more suited where labour is available and cheap. On the other hand, mechanically operated systems require a greater capital investment in equipment. Mobile systems minimise labour inputs by operating with motorised laterals or sprinklers, which irrigate and move continuously at the same time (Savva and Frenken, 2002).
Sprinkler irrigation efficiency is highly dependent on climatic conditions. FAO (1982) proposed the figures of farm irrigation efficiencies provided in Table 1 on the basis of climate.
Table 1: Farm irrigation efficiencies for Sprinkler Irrigation in different climates (the overall efficiency comprises conveyance efficiency, field canal efficiency, and field application efficiency)
|Climate/Temperature||Farm irrigation efficiency|
Source: adapted from FAO (1982)
Sprinkler irrigation technology can support farmers to adapt to climate change by making more efficient use of their water supply. This is particularly appropriate where there is (or is expected to be) limited or irregular water supply for agricultural use. The sprinkler technology uses less water than irrigation by gravity, and provides a more even application of water to the cultivated plot. Additionally, sprinkler irrigation can reduce the risk of crops freezing due to colder than usual temperatures. More frequent and intense frosts are already impacting on crops as a result of climate change. During the night, the motion of the sprinklers and the application of rain-like water droplets can reduce the stress on crops caused by a sharp decrease in temperature (Snyder and Melo-Abreu, 2005).
One of the main advantages of the sprinkler irrigation technology is more efficient use of water for irrigation in agriculture. Sprinkler systems eliminate water conveyance channels, thereby reducing water loss. Water is also distributed more evenly across crops helping to avoid wastage. The sprinkler irrigation system has also been shown to increased crop yields (Table 2) and is suited for most row, field and tree crops that are grown closely together, such as cereals, pulses, wheat, sugarcane, groundnut, cotton, vegetables, fruits, flowers, spices and condiments (Narayanmoorthy, no date) and for cultivating paddy crop (Kundu et al, 1998).
Table 2: Response of different crops to Sprinkler Irrigation Systems
|Water saving %||Yield increase %|
Source: adapted from INCID (1998)
Sprinkler irrigation technology is well adapted to a range of topographies and is suitable in all types of soil, except heavy clay. Sprinkler systems can be installed as either permanent or mobile fixtures. Sprinklers provide a more even application of water to agricultural land, promoting steady crop growth. Likewise, soluble fertilisers can be channelled through the system for easy and even application. The risk of soil erosion can be reduced because the sprinkler system limits soil disturbance, which can occur when using irrigation by gravity. In addition, sprinkler irrigation can provide additional protection for plants against freezing at low temperatures. Secondary benefits from improved crop productivity include income generation, employment opportunities and food security.
The main disadvantages associated with sprinkler systems are related to climatic conditions, water resources and cost. Even moderate winds can seriously reduce the effectiveness of sprinkler systems by altering the distribution pattern of the water droplets. Likewise, when operating under high temperatures, water can evaporate at a fast rate reducing the effectiveness of the irrigation. Although sprinkler irrigation can help farmers to use water resources more efficiently, this technology relies on a clean source of water and therefore may not be suited to areas where rainfall is becoming less predictable. Implementation costs are higher than that of gravity-fed irrigation systems and large labour force is needed to move pipes and sprinklers in a non-permanent system. In some places such labour may not be available and may also be costly. Mechanised sprinkler irrigation systems have a relatively high energy demand (Savva and Frenken, 2002).
The cost of installing a sprinkler system suitable for a family production unit ranges from US$ 600 to US$ 2500 per hectare, depending on the type of materials used and the amount of labour contributed by rural producers. Affordable Micro Irrigation Technologies (AMITs) are low cost and low pressure systems with the same technical advantages as conventional micro-irrigation system, however the technology is packaged and marketed as kits suitable for small fields (25 m2 to 4000 m2). The AMIT has the specific advantage of being affordable, and easy to understand; they also have rapid pay back, divisibility and expandability.
When planning to install a sprinkler irrigation system, information should be obtained regarding the following key factors:
- The crop or crops to be cultivated and their water requirements throughout the growing season
- The shape and size of the field. This will determine the range of suitable technologies, investment and labour requirements
- Topography, in particular the location and elevation of the water source relative to the field, land slopes and uniformity
- The water source. The source of irrigation water can be surface water, groundwater or non-conventional water (such as desalinated water and treated wastewater) (Savva and Frenken, 2002). Water must be available in sufficient quantity from a locally accessible source. A clean supply of water free of sediment is required to avoid blockage in sprinkler nozzles and crop spoilage (FAO, 1988)
- Available labour force. Where skilled labourers are not available on location, local farmers will require training to install, maintain and repair the various components of the sprinkler system
- The soil profile. Sprinkler irrigation technology is best suited to soils with high infiltration rates so that ponding and surface runoff can be avoided. The application rate of the sprinkler system must therefore be matched to the infiltration rate of the most restrictive soil in the field.
- Energy requirements of different systems, including the manufacturing, transportation and installation of the various systems. The location of the water source will also affect the need for energy for pumping (Savva and Frenken, 2002)
- Social aspects such as local preferences, capacity to maintain the system, implications for labour requirements and how these may affect different members of the community (Savva and Frenken, 2002)
- An understanding of existing health risks is crucial to avoid schemes that may promote water borne diseases (Savva and Frenken, 2002)
- An environmental impact assessment should be conducted to fully understand potential impacts of drainage and diverting water resources, amongst others (Savva and Frenken, 2002).
Maintenance of the system mainly relates to regular cleaning of the component parts. Seals on pipes and sprinkler nozzles should be checked to avoid water seepage. During periods when the equipment is not being used, it is recommended to store component parts in a cool, dark place.
According to Savva and Frenken (2002), a whole range of institutional conditions must be understood before sprinkler irrigation technology selection can be made. These include land tenure issues, water rights, and financial incentives by government and taxation. Large-scale irrigation schemes will usually form part of national policy and could be harnessed to support national employment initiatives. Where the sprinkler irrigation type is not available nationally, foreign imports or government-supported stimulation of national manufacture will be required alongside investment in training for design, installation and maintenance. Coordination with public or private authorities in charge of water management will be crucial and could be facilitated through the establishment of a committee of irrigation users. At a local level, social organisation for the participatory monitoring of water resources and quality could provide a key monitoring tool. Whichever method is selected, developing regulations for the distribution and allocation of water would provide an important mechanism for conflict resolution.
Whether a large or small-scale intervention, farmer involvement in the development stages of a sprinkler irrigation project is recommended to help ensure social acceptance and technical success (Box 1).
Box 1: Sprinkler irrigation in Zimbabwe
“The Hama Mavhaire irrigation scheme in Zimbabwe is a 96 hectare drag-hose sprinkler irrigation project. The scheme is apportioned equally to 96 farmers, of which 70 per cent are women. It is located in a dry agro-ecological area that receives about 450 mm of rainfall per year. Dryland cropping fails 3 to 4 years out of 5. The development of the scheme was initiated in 1989, following strong farmer requests to the government for irrigation development.
Participation of Farmers in Planning and Design
The government dispatched a team of experts, comprising engineers, agronomists and economists, to the project site to carry out a feasibility study. Several meetings were held in order for planners to understand the farmers’ expectations and to explain to the farmers the potential of and requirements for the proposed development. This was followed by a baseline socio-economic survey. The land chosen consisted of about 80 per cent of non-cultivated bush, while the remaining 20 per cent was arable land owned by the farmers who were selected for the scheme. The farmer group was to be the partner in irrigation development. It elected its own committee, which was tasked with liaising with the planners on all matters related to the new development.
To facilitate a process of making informed decisions, arrangements were made for farmers to visit different types of irrigation systems, surface and sprinkler. This exposure proved useful to farmers when they eventually decided on the type of irrigation system they preferred and the crops to be grown. This process took one full year.
Participation of Farmers in Construction
When the design was adopted, tender documents were written to include the condition that the farmers would provide all unskilled labour required for construction. During construction the group provided labour for trenching and back-filling and assisted pipe fitters by carrying and placing pipes and fittings in position. As a result of their participation, the farmers were trained in pipefitting and other general repairs to their system. Additionally, the contractor trained one farmer per irrigation block on the repair of sprinklers. The irrigation engineers and extension staff trained the farmers in leadership, bookkeeping, scheme operation, improved agronomic practices and irrigation scheduling. This process took six months for the first 48 hectares and three months for the remaining 48 hectares.
Socio-economic Impact of Scheme Development
On average, the net income per plot-holder quadrupled due to the introduction of irrigation, from a gross margin assessed at US$ 650 annually on 2.5 hectares of dryland crop production to a gross margin of US$ 2,775 for one hectare irrigated. There are other indicators of a substantial rise in the standard of living of the irrigators. About 29 per cent of the plot-holders are reported to have purchased between one and four head of cattle from the income earned through irrigation during the first five to six years of scheme operation. In addition, 13 per cent of the plot-holders had put up brick under corrugated iron houses and 10% had installed solar panels during the same period. Women, who constitute the majority of the plot-holders and are represented at all committees, also confirmed that the other major benefit of irrigation was that they are able to pay for the costs of educating their children.
The success of the Hama Mavhaire irrigation scheme is largely attributed to the participatory approaches adopted for the development of the scheme provided the opportunity to the group, planners and implementers to jointly plan and implement a scheme, making it both technically feasible and socially acceptable.”Source: Savva and Frenken, 2002
Possible barriers to implementation include lack of access to finance for the purchase of equipment, lack of local skills for design, installation and maintenance of the system and lack of nationally/locally available component parts. A low level of public awareness of or concern for the importance of sustainable water management and use could also be a barrier to the exploration of sprinkler irrigation technology as a climate change adaptation option.
Sprinkler irrigation requires a suitable source of fresh water to be identified in close enough proximity to the farmland. This ensures that costs are kept at a reasonable level. Water availability will be highly dependent not only on current resources but also on future climate conditions. Where knowledge of potential climate change impacts on water resources does not exist, installing a sprinkler irrigation system could lead to conflicts over local water use.
Sprinkler irrigation is a versatile technology suitable for application in a wide range of contexts, can be implemented at small or large scale and with either 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.
FAO (1982) Mechanised sprinkler irrigation. FAO Irrigation and Drainage Paper No. 35. Rome.
FAO (1988) Irrigation Water Management: Irrigation methods, FAO. Rome.
INCID (Indian National Committee on Irrigation and Drainage) ( 1998) Sprinkler Irrigation in India. INCID, New Delhi.
Kulkarni, S.A., F.B. Reinders and F. Ligetvari (2006) Global Scenario of Sprinkler in Micro-Irrigated Areas. Sept 10 – 16 2006, PWTC, Kuala Lumpur 7th International Micro Irrigation Congress
Kundu, D. K., H. U. Neue, R. Singh (1998) Comparative Effects of Flooding and Sprinkler Irrigation on Growth and Mineral Composition of Rice in an Alfisol. Proceedings of the National Seminar on Micro- Irrigation Research in India: Status and Perspective for the 21st Century. Bhubaneswar, July 27-28.
Narayanmoorthy, A. (no date) Drip and Sprinkler Irrigation in India: Benefits, Potential and Future Directions. Available: http://www.iwmi.cgiar.org/Publications/Other/PDF/Paper%2015%20of%20NRLP%...
Savva, A. P. and K. Frenken (2002) Irrigation Manual Planning, Development Monitoring and Evaluation of Irrigated Agriculture with Farmer Participation. Volume I Modules 1 – 6.
Snyder, R. L. and J. P. Melo-Abreu (2005) Frost protection: fundamentals, practice, and economics – Volume 1. FAO, Rome.