Drip irrigation for lawns.
More than a decade after its introduction to the gardening world, drip irrigation has become a household term. This system is widely used to water flower beds, vegetable gardens, landscape plants, and container plants. But what about lawns?
Until recently, lawns could be watered only with sprinklers. Reliable equipment for drip-watering lawns didn't exist. But recent developments with more sophisticated emitter lines have changed things.
Emitter lines are made of polyethylene tubing with drip emitters inserted in it at regular intervals. They've actually been around for a while, but their use in lawns was considered experimental by most irrigation specialists.
In recent years, independent researchers, such as those at the Center for Irrigation Technology (CIT) at California State University Fresno, have done enough testing that emitter lines are now recommended for many lawns.
The greatest recent improvement has been the infusion of an herbicide into the emitter plastic. The herbicide prevents root intrusion when emitter lines are buried in soil (the minute amount doesn't contaminate the soil). Products not protected by a chemical barrier often became clogged with roots.
The treated emitter line, by Geoflow, of Sausalito, California, has a reported life span of 20 years, which equals or surpasses that of many sprinkler systems.
THE ADVANTAGES OF DRIP IRRIGATION
The primary benefit of sub-surface irrigation is water savings. Because water delivery is below the soil surface, no water is lost from evaporation, runoff, or overshooting lawn boundaries. Emitter lines are particularly useful with irregularly shaped and narrow strips of lawn, and on slopes. Lack of overshooting also helps eliminate rotting and water stains on fences and house walls, and prevents slippery walkways.
Ali Harivandi, environmental horticulture adviser for UC Cooperative Extension in Alameda County, says a benefit for families is the lack of surface wetting. Because the lawn's surface is never soaked, it can always be used for activities. The incidence of disease - and need for toxic fungicides - is also greatly reduced when grass stays dry.
In addition, with the availability of emitters with different spacings, subsurface systems can be designed for berms and slopes to avoid wet spots at low points and dry spots at the tops.
CIT's research has shown that weed invasion may be significantly reduced in healthy, dense turf that's watered underground, since there is no surface moisture to encourage seed germination. CIT also found no adverse effects from gophers and other rodents, even though they were present in test sites. However, CIT doesn't recommend sub-surface drip in lawns that have competition from large trees with many roots, or in soils that are extremely porous or gravelly. The system costs 1 1/2 to 2 times as much as sprinklers, but drip irrigation specialists believe the advantages outweigh the extra expense, especially for irregularly shaped lawns.
HOW TO SET UP A SYSTEM
Emitter lines have either turbulent flow emitters (with wide channels so debris won't easily clog them) or pressure-compensating emitters (for slopes, hilly terrain, or especially long lines). For most situations, the more durable turbulent flow emitters are best.
The basic design for use in a lawn is sets of parallel emitter lines that run from a supply line to an exhaust line (see drawing on page 76). In most cases, the supply and exhaust lines are made of polyvinyl chloride (PVC). A PVC system is durable and easy to install, since the PVC provides a rigid framework.
You could use black polyethylene (drip) tubing, but "then you're wrestling with two things that curl - the emitter lines and the poly tubing," says Tom Bressan of the Urban Farmer Store in San Francisco. However, for small lawns and narrow planting strips, polyethylene is the simpler solution.
Emitter lines are easiest to install in a new lawn, although they can be installed in existing lawns using a small power trencher (available from equipment rental stores). This machine carves 1-inch-wide, 6-inch-deep trenches. The emitter lines are laid at the bottom, then the trenches are filled in and overseeded.
Layout of the emitter lines will differ according to the shape of the lawn, but the emitter lines always run parallel to one another and should be buried about 6 inches deep - 4 inches in very sandy soil. Soil type determines the flow rate of each emitter (1/2 to 1 gallon per hour), the spacing between emitters on the line, and the spacing between lines.
As a general guideline for clay soil, use 1/2-gph emitters spaced 18 inches apart with lines spaced 18 inches apart; for loam, use 1-gph emitters spaced 18 inches apart on lines 18 inches apart; for sandy soil, use 1-gph emitters spaced 12 inches apart on lines 16 to 18 inches apart.
At the bottom of a slope, place emitter lines about 25 percent farther apart than is recommended for your soil type; at the top of a slope, set them 25 percent closer.
HOW OFTEN TO WATER
Since the roots of new lawns need time to grow into the soil, it's best to surface-water new sod for the first couple of weeks after installation, and newly seeded lawns until the grass is established.
After that, learning how often to run your system requires some experimentation. Ideally, lawns should be watered according to evapo-transpiration (ET) rates, which are measured in inches per day or week and vary according to climate. This information is available from cooperative extension offices.
For instance, if you live in a mild-summer climate such as that of the San Francisco Bay Area, your lawn needs 1 1/4 inches of water per week. You can determine how long you need to run your system by using this formula:
Application rate (inches per hr.) = 231.1 (a constant) x Gallons per hr. (emitter rate)/Emitter spacing (in inches) x Lateral spacing (in inches)
Using a 1-gph emitter and 18-inch emitter spacing with lines spaced 18 inches apart (lateral spacing), the application rate would be 0.71 inches per hour. For 1 1/4 inches total, you need to run your sprinklers 1 3/4 hours a week. But the underground system should be run more frequently for shorter periods (the soil can't absorb that much moisture at one time), such as for 15 minutes daily or 17 minutes morning and evening three days a week.
WHERE TO GET EMITTER LINE
Treated emitter line from Geoflow is sold at most irrigation supply stores. Or you can order it by mail from the Urban Farmer Store, 2833 Vicente St., San Francisco 94116; (415) 661-2204 (catalog $1). The store also provides design assistance; call (800) 753-3747.
RELATED ARTICLE: CONNECTING IT ALL TOGETHER
Plan the system on paper first, to determine how much tubing and PVC pipe you'll need, along with the number of Ts and elbows. For most lawns, use 3/4-inch PVC pipe, and 1/2- or 1-gph emitters with 12- or 18-inch spacing.
For each run of emitter line (except at corners), you'll need two 3/4- by 3/4- by 1/2-inch slip-slip-slip (SSS) Ts and two compression fitting adapters [ILLUSTRATION FOR PHOTOS 1 AND 2 OMITTED]. For the corners, you'll need four 3/4-inch slip 90 [degrees] elbows, four 3/4- by 1/2-inch slip-slip bushings, and four compression fitting adapters for the elbows [ILLUSTRATION FOR PHOTO 4 OMITTED]; if you can find them, you can use 3/4- by 2-inch slip 90 [degrees] elbows instead of the 3/4-inch elbows, which allows you to skip the bushings.
Besides the tubing and PVC, you'll need an automatic anti-siphon valve (or a manual valve if you're not using an automatic controller); a 155-mesh filter, a 20- or 30-psi preset pressure regulator [ILLUSTRATION FOR PHOTO 3 OMITTED]; a valve box [ILLUSTRATION FOR PHOTO 5 OMITTED]; an automatic flush valve, one 3/4- by 3/4- by 3/4-inch SSS T, one 3/4- by 3/4- by 1/2-inch slip-slip-thread T, one 3/4- by 3/4-inch slip-thread 90 [degrees] elbow, one 3/4-inch male pipe thread by male hose thread, and one 3/4-inch hose shutoff [ILLUSTRATION FOR PHOTO 6 OMITTED]; and PVC pipe glue.
The antisiphon valve must be positioned a foot above the highest point on the system, and the automatic flush valve must be positioned at the lowest point on the system. If you don't use an antisiphon valve, you should install an air relief valve at the system's highest point.
Follow the diagram to put the system together. Use pipe glue to glue PVC pieces together. When glue is dry, insert emitter lines in compression fittings. After installation, flush the lines with the hose shutoff to remove all sediment. If a leak develops, dig down and repair it by splicing in a new section of tubing, using compression fittings; use the hose shutoff to flush the lines after repairs.
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|Title Annotation:||includes relate article|
|Author:||Swezey, Lauren Bonar|
|Date:||Jun 1, 1995|
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