Be it with controllers, pop-up spray heads or valves, irrigation contractors are continually seeking increased control of the water they apply to their properties.
Low volume irrigation is perhaps the most exact result of this search. For example, low volume irrigation offers contractors the ability to maximize the efficiency of the water they use by applying water directly to a plant’s root ball.
“On a good overhead spray system, you might get 85 percent irrigating efficiency,” said Willie West, special operations manager, Albuquerque Grounds Maintenance Inc., Albuquerque, N.M. “With a low volume system, though, you get between 95 and 100 percent of the available water actually making it to the plant. That’s the key.”
BRIEF BASICS. The term drip irrigation essentially explains how one method of low volume irrigation works. The water runs through a standard ½-inch riser to a single- or multi-port emitter. The water is then distributed by the emitter or carried to the desired application area through 1/8-inch capillary tubing.
The key to the technology, also referred to as point-source emission irrigation, is the ability to apply the water directly to a specific plant’s root ball, thereby minimizing the amount of water needed to apply the desired amount to the plant.
“Point-source emission irrigation involves running a tube directly to a plant to create a wetted area for one specific plant,” explained Jeanne Cantu, national sales and marketing manager, residential/commercial/government markets, Toro Irrigation, Riverside, Calif. There are, however, other methods of low volume irrigation. “Subsurface irrigation creates a blanket of water for an area through the use of tubing buried in the soil,” Cantu added.
Cantu noted that subsurface irrigation is traditionally used for broader applications such as ornamental beds or narrow areas that are difficult to irrigate with pop-up spray heads and anywhere contractors want to create an overall blanket of water. Contractors use tubing which has emitters installed every 12 to 18 inches in the tubing, and the water is applied directly through these emitters to the root area. The lines of tubing are laid in a grid format beneath the lawn with lines spaced 1 to 2 feet apart.
Cantu also noted that subsurface systems can be integrated with pop-up sprays and other irrigation systems. “The run times for these systems are similar enough to run on most standard clocks,” she said. “Contractors can match the application rates depending on the spacing of the subsurface emitters.”
TURF CHALLENGES. Manufacturers interviewed for a story in the March 1995 issue of Lawn & Landscape predicted that technology for widespread use of low volume irrigation in turf applications was just around the corner. However, manufacturers and contractors alike take something of a different position today.
“Unless there’s a real special reason to use it — such as hard-to-reach areas or isolated strips of turf — I don’t think we’ll ever see low volume irrigation used as a major method of irrigating turf,” announced Don Olson, president, Olson Irrigation Systems, Santee, Calif. “It’s good for median strips where the contractor has to avoid over-spraying onto roads, but it has too many potential problems for use in large areas of turf.”
“In most cases, pop-up spray heads are more cost efficient on wide expanses of turf,” agreed Cantu.
“The problem with using subsurface irrigation for turf is that the grid layout makes it difficult to get an even color of green throughout the turf,” noted West. “Depending on the soil composition, the water may not migrate evenly and then you get striping and stress. Plus, how do you apply granular fertilizer without having an overhead spray to break it down?”
“Typically, we don’t install subsurface systems for turf unless it’s to establish new seed,” noted Gene Trog, maintenance operations manager, Desert Care Landscaping Inc., Phoenix, Ariz. “On those occasions, we install the system on a separate valve. Once the turf is established, we discontinue the valve and just leave the system in the lawn.”
PLANT PLUSES. “Drip irrigation is really suited more for ornamental applications because you don’t have the plant population you have with turf, and it’s easier to target the applications,” according to Olson. “If the system is used in an ornamental bed, the contractor doesn’t have to worry about watering weeds in between the plants or wasting water on mulch.”
“We use drip irrigation systems on 100 percent of our shrubs and trees,” noted Dave Ramsze, regional vice president, The Groundskeeper, Tucson, Ariz., who emphasized the importance of proper design in order to maximize a system’s efficiency. “Systems should be designed with separate zones for each type of plant material so the flow and frequency can be set accordingly.”
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Doug Bennett, irrigation conservation manager for the city of Albuquerque, N.M., said the city ordinance in effect there is designed to eliminate water waste and reduce the amount of new landscaping that requires large quantities of irrigation. “The ordinance limits the use of plants on slopes and the use of turf less than 10 feet in any direction. It also requires that only 20 percent of new landscape installations require irrigation,” he said. “The ordinance has been written specifically to target design problems causing a waste of water.” Bennett noted that although it’s the property owner who is cited when failing to comply with the ordinance, the irrigation contractor for that property is inevitably affected as well. “My intent is to get our residents and commercial property owners to comply with the ordinance, so this applies pressure to the irrigation contractors if they want to get those jobs,” he said. “Some of the problem contractors are conscientious about their work, but they don’t know the basics of water management. Our priority is to educate them. If they don’t want to be educated, then they’ll probably fall by the wayside.” The ordinance is effective, according to Bennett. “We assessed 277 accounts for water waste violations in 1995,” he said. “In 1996, those accounts cut their water use by 101 million gallons.” |
Slope and elevation changes also demand design attention. “Elevation changes affect flow and low end drainage,” warned West. “Too many designers don’t consider the effects of different grades, so they’re stressing plants on top of a slope and drowning plants at the bottom.”
West attributed part of this problem to the recent boom in the use of low volume irrigation. “Check valves can handle slope changes, but the information and technology available isn’t being used. The systems have almost become too popular in the last two years.”
Larry Keesen, in his book, The Complete Irrigation Workbook, explained this idea further. “Twenty feet of elevation changes within the lateral line results in a 8.7-psi pressure change. If the system is operating at 20 psi, it represents nearly a 50 percent change in pressure,” he wrote.
Another common design error is placing the emitters too close to the plant material. “A proper design will run the polyethylene tubing 3 or 4 feet away from the plant and use distribution tubing to take the water to the root zone. But the water should be applied right at the drip line,” explained Ramsze, referring to the area of soil directly under the canopy of the plant. “Contractors have to move the tubing along with the drip line as the plant matures, but they don’t do that enough to encourage proper root growth.”
MAINTENANCE GAME. “You can turn sprinklers on and off to see if they’re working properly,” noted Trog. “But with subsurface systems, you have to activate the system, walk the system and check each emitter. Obviously, this takes a lot longer.”
West noted that higher quality materials used for the lateral lines and tubing have eliminated some maintenance problems. “The lines last a lot longer than they used to,” he said. “Now, we’re getting between five and 10 years out of a system.”
And what about the often cited problem of roots penetrating lines? “I’ve been working with these systems for 20 years now, and root invasion has really never been a problem for us,” discounted Ramsze.
West said he has encountered root penetration problems, but people forget one detail. “Root problems are rare, and in the situations where they do occur, you’d probably have the same problem with normal PVC line and pop-up spray heads,” he said.
The contractors agreed the key to minimizing maintenance problems is installing quality products. “Cutting cost is the most important thing to a lot of contractors when they’re installating irrigation, so they try to get more out of the equipment than is possible,” Ramsze explained.
DEAL WITH PRESSURE. The contractors interviewed commented that manufacturers have improved the quality of the components of low volume irrigation systems. “Emitters today are much better with the flushing capabilities and the filter screens,” commented Trog. “The manufacturers have eliminated a lot of the problems from emitters clogging.”
Along with flushing out debris when the system is activated, new emitters address pressure fluctuation problems facing contractors. “The key to successful performance in low volume systems is maintaining accurate flow levels,” explained Bob Yarnell, advertising and promotions manager, Bowsmith, Exeter, Calif. “Pressure-compensating emitters maintain consistent flow levels in pressures ranging from 3 to 60 psi.”
Yarnell said Bowsmith’s emitter employs a flexible diaphragm which reacts to the pressure of the water. “It closes off the output port with higher pressure, and it relaxes and opens up the output when there’s less pressure,” he said.
Don Hendrickson, manager, Hend-rickson Brothers, Corona, Calif., said the majority of contractors use pressure-compensating emitters now. “The pressure-compensating emitters sense the downstream pressure and regulate it to the preset level,” he said. “Then the system lines fill up as fast as they can and the emitter cuts down the flow until it reaches the desired level.
“Most pressure-compensating emitters are set at 1 or 2 gallons per hour at 20 psi, but contractors may use a 25-psi emitter so the emitter keeps running if the pressure gets a little too high,” Hendrickson continued.
“A big problem with some low volume systems is that the valves won’t close properly when the system is turned off because the valves are from broadcast irrigation systems that were retrofitted to low volume irrigation,” added Dick Greenland, director of marketing, Superior Controls Co., Valencia, Calif. “These valves weren’t built to close at such low flow levels.
Greenland explained that Superior Controls’ valves don’t allow water beneath the diaphragm so they don’t need as great a pressure differential over the diaphragm to close the valve. “If contractors question how well their valves are working, they should shut down the system and install valves they trust,” he recommended.
The author is Associate Editor of Lawn & Landscape magazine.
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