Groundskeepers Must Strive for Peak Irrigation Efficiency
Rainfall was already lagging 30 inches behind the 12-month norm when drought conditions spiraled out of control last July in Mesquite, Texas. For two solid weeks, high temperatures topped 105 degrees, baking the city's clay-based recreational sports fields as if they were in some giant meteorological kiln. Fractured soil and patches of brown turf characterized many fields — the usable ones. And in a cruel bit of irony, updates to the in-ground irrigation system at one of Mesquite's multipurpose venues had bared so much soil to the blazing sun that cracks on that field measured a full 12 inches wide and three feet deep, exposing the system's brand-new wiring strung 18 inches below the playing surface and rendering the renovated tract useless for the entire baseball and football seasons.
Leagues were shuffled among satisfactory game sites, and seasons shortened. Some associations took to filling cracks themselves to keep fields playable. Practicing on game fields was strictly prohibited. "Everyone had to make sacrifices," says Mesquite park services superintendent Travis Sales. "That's the only way we were able to work around it."
The biggest sacrifice took the form of water. With local lake levels depleted by as much as 17 feet, Sales had to scale back his irrigation regimen from three days per week to one weekly watering. Mandated restrictions coupled with evening playing schedules further dictated that watering take place only between midnight and 6 a.m. Fields fortunate enough to receive water did so only within their playing boundaries.
Far from ideal, such compromises were at least possible thanks to the automated in-ground irrigation system already in place on Mesquite park grounds. Forty-seven of 100 citywide irrigation stations, including those covering all athletic fields, are controlled by computer from Mesquite Park Services Division headquarters. Water waste is further curtailed by flow meters that detect leaky pipes and damaged sprinkler heads, then automatically shut down the affected station in favor of the next one in the irrigation sequence. "All in all, we made it through pretty well, but we are still far from being out of the drought," Sales says. "There are going to have to be permanent changes made to the way we water."
Though severe, the situation in Mesquite is not isolated. Climate patterns — even population surges — are foretelling future strain on our nation's natural resources. And ask any groundskeeper or agronomist: The single most important ingredient in successfully growing sports turf is water. "In certain parts of the country, such as the semi-arid West, you either have water or you don't have grass," says Iowa State University horticulture professor David Minner, who teaches a three-credit course focused solely on irrigation. "In other areas that receive fairly high rainfall, we use supplemental water there, too, because we're not only growing grass, we're growing it on cue. We're forcing it to grow. And because we don't tolerate brown grass during the playing season, we need supplemental irrigation systems."
Given the ever-increasing demand for recreational green space, not to mention the lofty expectations of today's end users, the pressure is on groundskeepers everywhere to deliver lush playing surfaces while ensuring that their irrigation practices meet peak efficiency. Says David Zoldoske, director of the Center for Irrigation Technology at California State University, Fresno, "I think large parks and athletic fields are going to come under increasing scrutiny to minimize the total amount of applied water in a given area."
"School districts are already under increased pressure," says Mike Tarantino. As grounds and operations superintendent of the Poway (Calif.) Unified School District near San Diego, Tarantino oversees 35 separate playing sites. "My elementary school, middle school and high school fields are used seven days a week, probably 365 days a year," he says. "All my fields are open to any community group that wants to use them — from Little League to Pop Warner to soccer, rugby, lacrosse and field hockey organizations."
Like most of his colleagues in California and throughout the Southwest, all of Tarantino's natural-grass fields — game and practice — feature in-ground irrigation. The investment in such technology becomes spottier as one travels east into more intemperate climates. "In the Midwest, some high school athletic directors and coaches, the decision-makers, don't think irrigation is important. They think it's a luxury," says Lynda Wightman, senior sales manager for irrigation manufacturer Hunter Industries and a member of the National Interscholastic Athletic Administrators Association's sports turf committee. "My job is to try to teach them about efficient irrigation — what they need to do to have an irrigation system and how they need to maintain it so that their fields are safe. It's not just about aesthetics; it's about safety."
Ensuring irrigation efficiency starts with a working knowledge of hydraulics, Wightman says. That means knowing where water is going to come from, at what pressure, through what type of equipment and layout, and under what kind of control. Sufficient pressure is needed to activate retractable sprinkler heads, the size of which can be specified based on available water pressure. The heads must be spaced so that the water they throw — typically anywhere from 30 to 90 feet, depending on available pressure and system design — at least reaches the next closest heads in the layout for complete, overlapping irrigation. This so-called "head-to-head coverage" means that a regulation-size football field will feature at least 21 retractable heads within its playing boundaries, and perhaps another 30 or more out of bounds. Heads should be no larger than two to three inches in diameter, capped in hard rubber and positioned so that the rubber cap is level with the finished grade when retracted. Ideally, heads on fields that receive regular top-dressing treatments are specified with swing joints, allowing them to be trenched out and manually raised every five to eight years as the soil profile steadily accumulates additional layers.
Due to pressure limitations, sports fields are typically irrigated in valve-controlled zones, with only a fraction of the sprinkler heads active at any given time. The addition of a booster pump can increase pressure and allow for the activation of a greater number of heads and even the simultaneous irrigation of more than one field. Care must be taken, however, to ensure that water traveling to the area doesn't exceed the accepted industry speed limit for PVC pipe of five feet per second. If too much water is forced through too small a pipe, pressure actually drops due to frictional losses caused by agitated water contacting more of the pipe's inner surface area. Too much pressure can also cause water hammer — the backlash exhibited by high-speed water flow once it hits an obstacle in its path, such as a "T" intersection or a 90-degree elbow within the design layout.
Efficient irrigation design also requires forethought. Experts recommend roughing in additional pipe for future expansion of in-ground systems to include adjacent fields, as well as specifying a sufficient number of quick couplers on any given field for manual watering, in the event of in-ground system failure.
Underground leaks and heads knocked out of alignment or damaged by mowers are among the biggest contributors to an established system's inefficiency. A tilted sprinkler head will spray the water at an improper trajectory, or perhaps even straight into the air, and a head whose rotary arc (adjustable from 45 to 360 degrees in some models) has come out of alignment may be watering bleachers instead of turf. In addition, all heads should pop high enough above the grass blades to avoid having their spraying distance inhibited by the turf itself. Wightman recommends semiannual or even monthly inspections of empty fields with the system on to ensure water is not being wasted. "Site inspections are cheap insurance policies," she says. Still, no system is perfect. Says Tarantino, the current president of the Sports Turf Managers Association's Southern California chapter, "If you get a system that operates at 75 to 80 percent efficiency, you're blessed."
Many turf managers with in-ground irrigation systems control their watering schedules based on evapotranspiration (ET), the combined loss of water through soil and grass plants that occurs naturally but at different rates depending on environmental conditions and field usage. Irrigation systems working in concert with an onsite weather station can be programmed to respond to changing ET rates automatically by replenishing the precise amount of lost water. "Blades of grass sweat just like we do when we're outside and it's hot, windy and not very humid," Wightman says. "We get a drink of water, but the plants can't do that. It's up to us to know how much the grass sweats on a given day so we can put the water back through the scheduling of the irrigation system."
ET data, which can also be gathered by contacting nearby universities or local meteorologists, is especially useful to those in charge of far-flung fields that can't be visually inspected on a daily basis. Moreover, the day-to-day monitoring of ET becomes increasingly critical in regions of the country (such as the Midwest) where weather conditions may vary widely within a 48-hour window, but less so in states such as California, where more consistent seasonal conditions are a given. "Once I get into summer," says Tarantino, who sees an average of nine inches of rain per year, mostly during the winter months, "I know what I'm going to get."
Groundskeepers able to walk their fields can still fall back on visual inspection to determine the turf's level of thirst. Footprinting — the inability of grass blades to rebound when stepped on — is an indication of incipient wilt, or a lack of turgidity within the plant. The grass may also exhibit a blue-green hue at this stage of stress. "It really doesn't hurt the grass," says ISU's Minner. "In fact, it makes roots grow." Adds Brad Waters, area specification manager for irrigation manufacturer Rain Bird, which will stage its sixth Intelligent Use of Water Summit this month in Madrid, Spain, "The deeper the roots, the less frequent your irrigation, typically, because deep roots can get available soil moisture easier than extremely shallow ones."
Irrigation isn't the only horticultural practice influencing root development, however. Mowing turf at low heights, while fostering denser turf growth to meet today's performance demands, actually retards deep root development. Thus, fields mowed at three-quarters of an inch will require more frequent irrigation than those mowed at two inches.
Minner recommends that turf managers master the art of recognizing when their fields reach a point of manageable stress, then put down just enough water to coax continued root growth. Turf on sand-based fields will begin to show signs of stress again in about three days, while it may take a soil-based field seven or more days to wilt. "Going through this cycle of what we call deep and infrequent watering allows the field to dry out," Minner says. "The drying period is good, because when it dries and wilts you know that there is sufficient oxygen in the root system. If you're watering so you never see any wilt at all, then you are probably over-watering. You probably have a lack or reduced amount of oxygen in the root zone."
It's even useful for those with irrigation systems featuring computerized controls to learn to visually recognize their turf's point of incipient wilt, according to Minner. "These systems can be so automated that the tendency is to turn them on, walk away and let that little electronic box think for you," he says. "I usually train people to turn the automated part off, learn what their grass needs are, then come back and use the automated part for times they're away."
The future of sports field irrigation may be no easier to forecast than average yearly rainfall totals, but one thing remains readily apparent: Grounds maintenance personnel need to take a closer look at their watering practices. By the time 2006 was declared the hottest year on record in the United States, British scientists had already predicted that 2007 would be the warmest ever worldwide. If available water again becomes scarce, sports field administrators can expect to see a trickle-down effect that starts with residential watering restrictions. "Turf is a threatened species," says Fresno State's Zoldoske. "I'm not saying that anybody's ever going to talk about banning sports fields, but I think they're going to look a lot closer at how much water is being allocated to grow turf, and there are going to be ever-increasing pressures to do more with less."
Those in Mesquite are already feeling the heat. Upon learning of the climatic challenges this summer may bring, Sales admits that his heart skipped a beat. "Right now, we're at a point where there's very limited water to feed our system," he says. "We're doing everything we can as far as having the most state-of-the-art equipment, keeping it in good running shape, having the sensors to detect leaks and shut the systems off immediately so that we don't waste water. The problem is we don't have the water available to have those systems do what they're supposed to do. That's scary."
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