- Increase understanding of irrigation efficiency, losses, and distribution uniformity associated with microirrigation.
- Increase understanding and application of best management practices to improve efficiency and uniformity of microirrigation.
- Key Points:
- Microirrigation offers potential for high water, energy and fertilizer efficiency and good distribution uniformity. These can result in good crop response (yield and/or quality) to irrigation and agronomic inputs.
- Microirrigation, like other advanced irrigation technologies, yields best results when properly designed, installed, maintained and managed.
- Microirrigation is well-suited to automation. While it can offer labor savings, these savings can be offset by increased management requirement.
- Water quality is especially important in microirrigation applications. Biological, chemical and physical clogging of emitters generally can be prevented through appropriate filtration and use of chemical additives as needed.
- Flow meters and pressure gauges can be very helpful in monitoring system performance and in trouble-shooting.
- Some potential problems encountered with microirrigation can include rodent and insect damage to tape and components; clogging of emitters and components; and problems with germination and crop establishment (especially with coarse soils in arid areas).
- Assess your knowledge:
- List 3 advantages and 3 limitations of microirrigation. Briefly discuss each in context of applicability to your farm operation.
- Explain why it is desirable to have multiple irrigation zones in a microirrigation system.
- Briefly describe 3 commonly used types of filters used in microirrigation. How does each work? How does an automated backflushing filtration system work?
- What is the primary purpose of acid injection into subsurface drip irrigation systems? How is the amount of acid necessary to accomplish this purpose determined? (How do you know how much acid to use?)
- What is the primary purpose of chlorine injection into subsurface drip irrigation systems? How is the amount of chlorine necessary to accomplish this purpose determined? (How do you know how much chlorine to use?)
- Describe how pressure gauges and flow meters can be used to identify potential problems in a microirrigation system.
Microirrigation, including microspray, surface drip and subsurface drip irrigation methods, can deliver water precisely and efficiently. Microirrigation is commonly used for irrigation of high value horticultural crops, orchards and vineyards. Subsurface drip irrigation (SDI) is gaining popularity in production of agronomic “row” crops, especially in areas of limited well capacities and where small or irregularly shaped fields give SDI a competitive advantage over other irrigation technologies and methods.
- Key Components
Microirrigation systems typically work at relatively low pressures. A pump should be correctly sized to deliver required flow and pressure, taking into account system operating pressure, lift(s), friction and dynamic pressure losses, etc.
Filters are key to protecting the irrigation system from plugging by suspended solids in the water.
Depending on the type of filtration system, a pressure sustaining valve may be needed to facilitate flushing of the filters.
Pressure gauges should be used at the inlet and outlet points of the filters to show pressure differential for initiating flushing of the filters.
A backflow preventer prevents backflow of fertilizers, chemicals, or particulates into the water supply and are installed between the water supply or pump and the chemical injection line.
A regulation valve helps to maintain proper operating pressure in the irrigation lines.
A chemical injector precisely injects chlorine, acid, fertilizers or pesticides into the irrigation stream.
A flow meter measures the volume of water moving through the system, either as a flow rate or as an accumulated total volume basis.
Chemigation line check valve is installed between the injector and the water source. It prevents backflow of water into the chemical supply tank in case of injector failure. This valve is often an integral part of an injector unit and can handle both backpressure and backsiphonage.
Zone valves are opened or closed to control the flow to appropriate zones. They may be manual or automatically controlled using and electronic control system.
Pressure regulators are typically located on the manifold to help regulate operating pressure for emitters.
Air and vacuum relief valves prevent soil or particulate material from being sucked back into emitters when the irrigation system is turned off or when driplines are drained.
Main line, sub-main lines supply water from the system head to the manifolds which subsequently distribute the water to the driplines. The dripline is the polyethylene tubing that includes a built-in emitter. Emitter spacing and rate are selected to match crop demands and soil water-holding capacity.
Flush lines at the tail end of the system serve three purposes: 1) Allow any sediment and contaminants to be flushed from dripline laterals at a centralized location, 2) Equalization of pressure in the dripline laterals, and 3) Allow positive pressure on both sides of a dripline break to prevent soil ingestion into the dripline.
Connectors are needed to attach the dripline to the manifold or submain. The number and type depend on system layout. There are many types of connectors. Connector options include glued, grommet, barb, and compression.
Electronic controllers allow for automation of irrigation applications to irrigate selected zones based upon set times, volumes, etc.
- Maintenance Considerations
A properly designed and maintained microirrigation system should last more than 20 years. A maintenance program includes cleaning the filters, flushing the lines, adding chlorine, and injecting acids. If these preventive measures are done, the need for major repairs, such as replacing damaged parts, often can be avoided, and the life of the system extended.
One goal of preventive maintenance is to keep the emitters from plugging. Emitters can be plugged by suspended solids, magnesium and calcium precipitation, manganese-iron oxides and sulfides, algae, bacteria, and plant roots. Every system should contain a flow meter and pressure gauges—one gauge before the filters and another after the filters. Daily monitoring of these gauges will indicate whether the system is working properly. A low pressure reading on a pressure gauge can mean that a part is leaking or a pipe is broken. A difference in pressure between the filters may mean the system is not being backflushed properly and that the filters need to be cleaned. Gradual increasing pressure with reduced flow can indicate an emitter clogging problem.
Maintaining filters. The filter is important to the system’s success. Water must be filtered to remove suspended solids. There are three main types of filters: cyclonic filters (centrifugal separators); screen and disk filters; and media filters. It is common practice to install a combination of filters to deal with various particulate sizes effectively.
Flushing lines and manifolds. Very fine particles pass through the filters and can clog the emitters. As long as the water velocity is high and the water is turbulent, these particles remain suspended. If the water velocity slows or the water becomes less turbulent, these particles may settle out. This commonly occurs at the distant ends of the lateral lines. If they are not flushed, the emitters will plug and the line eventually will be filled with sediment from the downstream end to the upstream end. Systems must be designed so that mainlines, sub-mains, manifolds and laterals can all be flushed. Mainlines, sub-mains and manifolds are flushed with a valve installed at the very end of each. Lateral lines can be flushed manually or automatically. It is important to flush the lines at least every 2 weeks during the growing season, or as needed based upon local conditions.
Injecting chlorine. At a low concentration (1 to 5 ppm), chlorine kills bacteria and oxidizes iron. At a high concentration (100 to 1000 ppm), it oxidizes organic matter and effectively removes it from the system.
Injecting acid. Acids are injected into irrigation water to prevent or treat plugging caused by precipitation of calcium carbonate (lime), magnesium and some other salts. Water with a pH of 7.5 or higher and a bicarbonate level of more than 100 pm is likely to have problems with lime precipitation, depending on the hardness of the water. Maintaining a low pH (6.5 or less) can generally prevent chemical precipitation and subsequent plugging of emitters; alternately periodic shock acid injection (temporarily lowering the pH below 4) can prevent build-up of precipitates.
- Advantages and Limitations of Microirrigation
Advantages of microirrigation (properly designed, installed, maintained and managed):
- High efficiency and uniformity of water application.
- Precise application of fertigation and chemigation.
- Reduced labor requirement compared to other irrigation technologies.
- Water use efficiency (water conservation and/or crop yield/quality response to water).
- Applicable to operations with large or small water capacities and over a range of field sizes, topographic and soil conditions.
- Reduced problems with annual weeds.
- Well suited to automation.
Limitations of microirrigation (depending upon local conditions):
- High initial cost.
- Maintenance and operation require higher level of skilled management than other irrigation systems.
- Potential problems with emitter clogging, root intrusion, rodent and insect damage.
- Potential problems with germination of a crop.
- Limited root zone.
- Limited options for deep tillage and deep injection of chemicals that may be needed for pest and disease management.
- Basics of Microirrigation (B-6160)
- Installing a Subsurface Drip System for Row Crops (B-6151)
- Maintaining Subsurface Drip Irrigation Systems (L-5406)
- Subsurface Drip Irrigation (SDI) Components: Minimum Requirements (MF-2576)
- Subsurface Irrigation Systems Water Quality Assessment Guidelines (MF-2575)
- Irrigation System, Microirrigation (441-1)
- Subsurface Drip Irrigation Information on the Internet