It’s July – Smart Irrigation Month. What better time to consider all of the technologies a contractor can employ to irrigate in the most efficient way possible? The results, no doubt, will be cost and water savings for clients and landscapes with healthy, vibrant plants.
One product category contractors may want to consider, or reconsider, are soil-moisture sensors (SMS). Though SMS have been around for more than 50 years, many contractors have hesitated to use them because the technology was historically unreliable. But industry experts say they deserve another look, as the SMS of today yield average water savings of about 40 percent. In addition, the Environmental Protection Agency’s WaterSense program is researching SMS along with weather-based controllers for its product labeling program, which is similar to the EnergyStar program for electrical appliances. With the consumer awareness on the rise – and the ever-increasing demands on the nation’s water supply – this is one area contractors can’t afford to ignore.
Dana Lonn, director of Toro Co.’s Center for Advanced Turf Technology, Bloomington, Minn., says SMS deserve another look from contractors. “In the past, many of the soil-moisture sensors used consumable parts like gypsum blocks that would degrade over time,” he says. “Today, most soil-moisture sensors are based upon microelectronics. Properly packaged to protect the electronics, they will last forever and will give us extremely accurate measures of volumetric water content.”
THE RUNDOWN. There are several types of SMS on the market, says Tom Penning, president of Riverside, Calif.-based Irrometer Co., a manufacturer of SMS. Some soil-moisture sensors are modules designed to be added on to irrigation controllers, and some irrigation controllers themselves possess soil-moisture sensing capabilities.
The way in which sensors measure soil moisture varies by manufacturer, but it’s generally measured either by the water tension in the soil or from a volumetric standpoint. Typically, the sensors are engaged when a controller sends a signal to irrigate. The sensor checks the water content in the soil and if the measured soil moisture is above the user-entered threshold, the controller will not irrigate. One of the major benefits of SMS is they fully take advantage of any rainfall events, Penning says.
Soil-moisture sensors can save big, manufacturers say. And they’ve been backed up by researchers including the University of Florida’s Michael Dukes, whose 2004 residential study in Florida concluded soil-moisture sensors saved an average of 59 percent more water than a system run by a time clock set according to historical evapotranspiration (ET)-based irrigation schedule with a rain sensor.
Dukes also confirmed a common manufacturer claim: In regions with a relatively high cost of water, property owners who install SMS can see a return on their investment in less than a year because of the water they’ll save. “As Florida’s population and accompanying residential communities continue to expand, there will be an even greater drain on existing freshwater supplies,” Dukes says in a summary report of the study. “Soil-moisture sensors are an inexpensive and effective way to conserve this important resource.”
CASE IN POINT. In Las Vegas, Russ Griffin, president of Private Greens of Nevada, is pleased with the results he’s seeing in his first year using SMS. Like in Florida, water conservation is top of mind in dusty, arid Las Vegas where population is rising as quickly as Lake Mead, the city’s main water supply, is receding. The lake’s water level has dropped approximately 100 feet since January 2000. The Southern Nevada Water Authority promotes a number of programs for saving water, like offering property owners $1.50 per square foot of grass removed with no cap on the maximum square footage.
That incentive doesn’t sit well with everyone, despite the SNWA’s estimate that every square foot of grass replaced with xeriscaping saves an average of 55 gallons of water per year. Many of Griffin’s clients covet their lush, green yards for their lifestyle and environmental benefits. He believes soil-moisture sensors may be the answer for his turf-loving customers.
In January, Griffin installed three SMS at a Las Vegas homeowners’ association site. In both 2006 and 2007 the HOA consumed nearly 1.9 million gallons of water during the first five months of each year. This year, during the same period, the site has used only a little more than 1.2 million gallons – a 30-percent reduction. The HOA paid about $350 per installed soil-moisture sensor, Griffin says. The investment will pay for itself by year’s end, Griffin says.
SMS VS. ET. Naturally, industry members are considering how SMS work alongside or instead of other “smart” technologies, like ET controllers and rain sensors. Though both ET controllers and SMS automatically adjust without user intervention, SMS awareness lags behind. “The Center for Irrigation Technology did testing protocols for ET technologies several years ago and are just now finishing the testing protocols for sensor-based systems,” says Kingsley Horton, western states sales manager for SMS manufacturer Acclima, Meridian, Idaho. He expects the CIT tests, WaterSense exposure and increased contractor testing to improve the use of SMS in years to come.
The Nelson Team, a full-service landscape company in Leeds, Ala., is one company that’s in the SMS testing phase. “Until recently, soil-moisture sensors weren’t reliable in our opinion,” says owner Joe Nelson. “Some manufacturers had them on the market and then pulled them, and there were reliability problems relating to the chemistry in the soil. But in my mind, they’re at the point where they’re probably going to be reliable. But I tend to be cautious, so I’m testing them before I sell them to customers just to make sure I’m confident.”
As for the SMS vs. ET debate, Toro’s Lonn says both are good technologies that can result in efficiency gains. “ET does a very good job of tracking climate,” he says. On the other hand, ET doesn’t read rainfall; it estimates how much rainfall may have made it into the soil.
ET controllers also don’t account for other non-climate issues that create a need for disrupting irrigation says Brian Lennon, sales manager for Irrometer. “For example if pipes break and lawns are flooded, ET wouldn’t know that.”
Lonn adds, “Soil-moisture sensors have the advantage that they measure actual soil moisture, so they measure the effectiveness of rainfall and the vigor of the plants,” he says.
Nelson, who’s a partner in the EPA’s WaterSense program, puts it plainly: “I may be wrong, but if I’m a plant and I want someone to know when to water me and I feed myself from my roots, then they need to know how much water is in my roots. Soil-moisture sensors are the best way to know that.”
SMS do have drawbacks, however. For example, they are limited to measuring only a specific point in the landscape, Lonn says. “ET has the advantage that it is less critical to local issues such as sensor placement which may prove important in the long run,” he says.
Nelson has gone over the SMS vs. ET debate himself, and he’s leaning toward soil-moisture sensors, though he’s testing both.
Nelson says he’s been cautious when selling all smart technologies to his clients. “When you go to your customer base, you have to be confident,” Nelson says. “Rain sensors are an easy sell, for example; customers understand those. But with ET, they don’t really understand it. So I didn’t want to push ET and then come back two years later with soil-moisture sensors or another technology and say ‘Wait, I’ve got something better.’ So I’m trying to skip a step and start with soil-moisture sensors.”
There’s another perception issue contractors have to mitigate when it comes to SMS: irrigating in the rain. “You have to use them in conjunction with rain sensors,” Nelson says. “It takes a period of time for the sensors to know it’s raining, and you do not want your systems running in the rain before the soil-moisture sensor knows it’s raining.”
Nelson expects to begin selling soil-moisture sensors by year’s end to his 80-percent residential customer base. He’ll start first with new installations and then target existing customers for retrofits. He is not sure yet how his customers will receive the SMS, which will be $400 to $600 per upgrade, but Nelson plans to sell them the same way he does drip irrigation. “What you can do is show them the payback,” Nelson says. “You say, this will cost you $500, but you’ll save X amount of water and get you payback in one to four years, depending on the client.” LL
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