Drip and Micro-Spray Irrigation Introduction
Simcha Blass, an Israeli hydraulic engineer, is credited with the discovery and introduction of modern drip irrigation in the early 1930’s. Drip irrigation (also known as micro-irrigation) became more common with the introduction of plastics in the 1950’s. Plastic tubing provided an inexpensive, flexible means of delivering water to the root zone of plants and was widely used in greenhouses and for agriculture. As improvements were made to the materials and problems such as clogging were resolved drip irrigation began to gain popularity for residential and small commercial applications. The relative simplicity of drip irrigation even made it possible for homeowners and other non-professionals to install it.
Drip irrigation is arguably the most efficient method of providing water to trees, crops, gardens and landscapes. The efficiency of overhead irrigation, such as rotors, and pop-up sprayheads is typically 50 percent and rarely exceeds 70 percent. The efficiency of a well-designed drip irrigation system can reach nearly 100 percent. Drip has numerous other benefits as well:
- It can be tailored to deliver the precise amount of water required by individual plants
- Evaporative losses are very low particularly when used in conjunction with mulch
- It is the best type of irrigation for windy conditions
- It uses less water since water is delivered only to the plants that need it
- It results in fewer weeds because the area between plants is not irrigated
- It reduces the incidence of foliar diseases
- It reduces or eliminates pollution from runoff
- It improves plant health by delivering fertilizer, and other chemicals precisely where they are needed
- It improves plant health by reducing fluctuations in soil moisture
- Its flexibility allows the system to adapt as plants grow or are added or removed
- It is well adapted for a wide variety of soil conditions and terrain
- It is often exempt from watering restrictions because it is so efficient
- Large areas can be watered all at once because of its low flow rate
- Installation and maintenance costs are typically much lower than for that of an underground sprinkler system
- It operates at pressures between 15 and 30 psi eliminating the need for a booster pump in low pressure systems
Some contractors are reluctant to use drip irrigation despite its many advantages. The reason most commonly cited is the inability to see if it is working. Not only is there no obvious spray pattern as with overhead irrigation – drip irrigation is typically covered by a layer of mulch several inches thick. Other disadvantages include:
- Subject to damage from other landscaping activities
- Subject to chewing damage from rodents
- Subject to vandalism, particularly in areas that haven’t been mulched
- Can present a tripping hazard for children and pets (anchoring tubing and covering with mulch can reduce this problem)
- Emitters can become clogged effectively shutting off water to portions of the landscape (improvements to system filtration and self-cleaning emitters have eliminated many of these problems)
- Can limit plan root growth to wetted drip area
Drip irrigation systems require regular inspections and maintenance to achieve optimal performance. Drip irrigation should be inspected several times a season for:
- Clogged emitters – if clogging is a frequent problem install a filter at the beginning of the system. Upgrade emitters with turbulent flow emitters to reduce problems with clogging.
- High pressure – missing emitters may be an indicator of high pressure. A pressure regulator should be installed if missing or replaced if damaged.
- Emitter spacing – as plants grow emitters must be moved to accommodate expansion of the root zone. Emitters may be moved inadvertently during weeding and other horticultural practices.
- Missing emitters – any missing emitters should be replaced immediately to maintain the efficiency of the system. Missing emitters may be an indicator of high pressure – check to make certain a pressure regulator is installed and functioning.
- Damaged tubing – tubing can be cut or pinched as a result of horticultural practices or plant overgrowth. Damaged tubing may need to be replaced, straightened or moved.
Tampa Bay Water has published A Guide to Micro-Irrigation for West-Central Florida Landscapes - available for free download here. Although the guide was written specifically for Florida homeowners, much of the information provided is broadly applicable and can be easily adapted for most regions.
Micro-spray is a cross between surface spray irrigation and drip irrigation. It has some of the advantages and some of the disadvantages of each type of irrigation. Like drip irrigation, micro-spray is considered a type of low-pressure irrigation typically operating with pressures between 15 and 30 psi. It is generally considered low volume with application rates of 5 to 70 gallons per hour (gph) (18.9 Lph to 264 Lph). Micro-spray typically creates a larger wetted area then drip irrigation making it well suited for irrigating ground covers, large flowerbeds and sandy soil.
Micro-spray is delivered through micro tubing to a series of nozzles attached to risers. These risers may be fixed or designed to pop-up. In either case, it is easy to see that they are functioning, eliminating the most commonly voiced complaint about drip irrigation. It provides many of the same benefits as drip irrigation with a few exceptions:
- It is less likely to be exempt from watering restrictions because it puts out a higher volume of water than drip irrigation
- It is subject to evaporative losses and spray pattern disruption in windy conditions
- Higher flow rates make it more susceptible to overwatering and runoff
- Larger wetted areas may result in more weeds
Micro-spray maintenance is similar to that of drip irrigation although it uses nozzles instead of emitters to deliver water. Nozzles are subject to clogging and disruption of flow pattern. Nozzles can be blown off due to high pressure; tampering with flow adjustments can result in flows that are too high or too low for the landscaped area being irrigated.
Additional resources on drip and micro-spray irrigation
http://www.ext.colostate.edu/PUBS/Garden/04702.html. Colorado State University Extension. Drip Irrigation for Home Gardens. No. 4.702. C. Wilson and M. Bauer.
http://www.cropinfo.net/drip.htm. Malheur Experiment Station. Oregon State University. Drip Irrigation: An Introduction. EM8782. C.C. Shock.
http://www.irrigationtutorials.com/dripguide.htm. Drip Irrigation Design Guidelines. Jess Stryker.
 A Guide to Micro-Irrigation for West-Central Florida Landscapes