The sprinkler or overhead irrigation system consists of conveying water to the field by aluminum or polyvinyl chloride (PVC) pipes and allowing it to sprinkle over the field under pressure through a system of nozzles. This system is designed to distribute the required depth of water uniformly to the crops which is not possible in surface irrigation. Here water is applied at a rate less than the infiltration rate of the soil and hence the runoff from irrigation is avoided.
Components of the sprinkler irrigation system -
A sprinkler system usually consists of the following parts -
- A pumping unit
- Tubing – mains, sub-mains and laterals (pipelines)
- Other accessories such as Filter, valves, bends, plugs and risers
Pumping unit: A high speed centrifugal or turbine pump is installed for pumping water under pressure.
Tubings or pipe lines: Pipelines are generally of three types. Main, sub-main and lateral. Main pipelines carry water from the pump to many parts of the field. In some cases, sub main lines are provided to take water from the mains to laterals. The lateral pipelines carry the water from the main or sub main pipe to the sprinklers. The pipelines may be permanent, semi-permanent or portable as per the requirement of the land where it is used.
Couplers: They provide connection between two tubing's and between tubing and fittings..
Sprinklers: Sprinklers may rotate or remain fixed. The rotating sprinklers can be adapted for a wide range of application rate and spacing.
Fixed head sprinklers are commonly used to irrigate small lawns and gardens.
- Water meters - It is used to measure the volume of water delivered.
- Flange, coupling and nipple - For proper connection to the pump and suction delivery
- Pressure gauge - It is necessary to know whether the sprinkler is working with the desired pressure in order to deliver the water uniformly.
- Bends, tees, reducers, elbows, hydrants, butterfly valves, end plugs and risers
- Fertilizer applicators - These are available in various sizes. They inject fertilizers in liquid form to the sprinkler system at a desired rate.
- Filters - This is needed when water is obtained from streams, ponds, canals or other surface supplies to filter the debris like sand, weed seeds, leaves, sticks, moss and other waste materials that may otherwise plug the sprinklers. It is not required when water is pumped from wells.
Types of sprinkler system -
Based on the arrangements for spraying irrigation water, sprinkler systems are classified into:
- Rotating head (or) revolving sprinkler system
- Perforated pipe system
Rotating head (or) revolving sprinklers
This can again be sub-divided into 3 categories -
1. Conventional system/small rotary sprinklers
2. Boom type and self propelled sprinkler system
3. Mobile rain gun/large rotary sprinklers
Perforated pipe system has no such further sub-divisions.
There are three types of spraying systems:
a. Stationary b. Oscillating c. Rotating
Based on the portability, sprinkler systems are classified into the following types.
1. Portable system 4. Solid set system
2. Semi portable system 5. Permanent system
3. Semi-permanent system
1. Portable system
It has portable mainlines and laterals and a portable pumping unit
2. Semi portable system
A semi portable system is similar to a fully portable system except that the locations of the water source and pumping plant are fixed.
3. Semi permanent system
A semi permanent system has portable lateral lines, permanent main lines and sub-mains and a stationary water source and pumping plant. The mainlines and sub mains are usually buried, with risers for nozzles located at suitable intervals.
4. Solid set system
A solid set system has enough laterals to eliminate their movement. The laterals are placed in the field early in the crop season and remain as they are for the season.
5. Permanent system
It consists of permanently laid mains, sub mains and laterals and a stationary water source and pumping plant. Mains, sub mains and laterals are usually buried below the plough depth. Sprinklers are permanently located on each riser.
Advantages of using sprinkler irrigation system -
- Economical use of water - with the available water, 2-3 times more area can be irrigated than the traditional irrigation practices..
- Low water loss - water loss is estimated as 18% as against 54% in surface irrigation with lined channels and 71% in a system without any lining.
- Effective water management - Water application is controlled. Over or under irrigation is avoided.
- Saving in land - It helps to conserve water up to 70% and can irrigate 2-3 times the area compared to surface irrigation.
- Saving in fertilizers - even distribution and avoids wastage of fertilizers.
- Land levelling is not necessary.
- Soil is conserved.
- Soil condition is maintained.
- Soil is stabilized.
- Seed germination is assured.
- Free aeration of the root zone is possible.
- Drainage problems are eliminated.
- Weeds and pests controlled since there is no possibility of water stagnation at all.
- Improved soil fertility and presence of beneficial soil organisms is maintained.
- High crop yield and quality.
- Reduced cost of cultivation.
Disadvantages of using sprinkler irrigation system -
1. Very high initial cost of installation.
2. Efficiency is seriously affected by windy weather.
3. Higher evaporation losses from spraying water.
4. Not suited for rice and jute where water stagnation is required.
5. It cannot be used on heavy clay soils.
6. Higher power requirements and thus expenditure for electricity is a grave concern.
7. Distribution is limited compared to other forms of irrigation..
8. Some of the irrigation water is lost by infiltration into the underground.
9. A stable water supply at all times is needed for the most economical use of the equipment.
The present era can be undoubtedly called the era of modernization, but the future epoch must be regarded as the age of sustainability. Otherwise, the vital natural resources like water, air, fossil fuels, etc. will come to an end very soon. As we can clearly see the number of advantages heavily outnumber the number of disadvantages for the sprinkler irrigation system, hence it should be positively used for irrigation purposes gradually substituting the traditional surface irrigation for the purpose of conservation of water.