Soil moisture monitors help sprinkler systems save water, money, says UF expert

July 21, 2005

GAINESVILLE, Fla. — The cost of keeping a lawn green could get lower, thanks to soil moisture monitors that make automatic sprinkler systems more efficient, says a University of Florida researcher.

The devices can cut sprinkler system water usage by more than half, according to a recent UF study. The findings were presented at the annual meeting of the American Society of Agricultural Engineers July 17-20 in Tampa.

Soil moisture monitors continuously check soil moisture levels and prevent sprinklers from operating when watering is not needed, said Michael Dukes, an assistant professor of agricultural engineering with UF’s Institute of Food and Agricultural Sciences. The monitors are not widely used despite being available for more than a decade.

On average, U.S. homeowners use almost 50 percent more water outdoors than indoors, according to a 2000 report by the American Water Works Association. Because lawn care accounts for most outdoor water use, homeowners who reduce unnecessary irrigation can save big on water bills, he said.

Sometimes, reduced watering can even improve a lawn’s health – overwatering encourages shallow root growth, which makes turfgrass less resistant to stress and more susceptible to some diseases, he said.

The soil moisture monitors Dukes tested are marketed as accessories for automatic sprinkler systems that use timers to schedule irrigation. These systems are convenient to use but often wasteful, he said.

“We conducted a survey of Florida homeowners from 2002 to 2004 that showed mostly-grass landscapes are typically given two-and-a-half times the water they need,” he said. “The monitors we studied, priced from $75 to $350, could pay for themselves within one year in areas where the cost of water is high.”

Dukes’ six-month study evaluated four commercially available soil moisture monitors, using them with timer-based sprinkler systems on UF turfgrass research plots. For comparison, he also tested timer-based systems with no water-saving devices as well as systems equipped with shutoff devices called rain sensors.

Rain sensors are popular water-saving options for automatic sprinkler systems, but because they measure rainfall rather than soil moisture, they may not determine a lawn’s water needs accurately, Dukes said.

The UF study showed systems equipped with soil moisture monitors used 56 percent less water on average than systems with rain sensors when the timers were set to water twice a week. Systems with the monitors used 70 percent less water on average than systems without water-saving devices on a twice-weekly watering schedule.

Use of the soil moisture monitors did not produce visible differences in turf quality, Dukes said.

The monitors are particularly suitable for residential landscape irrigation because they require little effort from homeowners, he said.

“For a timer-based system to be water-efficient in a climate like Florida’s, it has to be adjusted seasonally to account for heavy rains in the summer and reduced water requirements in the winter,” Dukes said. “Homeowners can avoid that inconvenience if the sprinkler system adjusts to soil conditions on its own.”

Soil moisture monitors are composed of two elements: sensors that track the soil’s water content and an electronic controller that can override the sprinkler system’s watering schedule if the sensors indicate the soil is sufficiently damp. The sensors, which detect moisture by measuring how well the soil conducts electricity, are buried three or four inches underground to monitor the region where turfgrass roots are densest, he said.

Soil moisture monitors have improved in the 25 years since the technology was developed, said Brent Mecham, a landscape water management and conservation specialist with the Northern Colorado Water Conservancy District in Berthoud, Colo.

The devices will have to overcome some skepticism to gain a foothold in the residential market, Mecham said. Some users have had bad experiences with soil moisture monitors, but he believes problems are often related to poorly planned or improperly maintained sprinkler systems.

“People who install one of these devices should understand it will take some time to fine-tune its performance,” he said. “But we need to learn to trust this technology – we need better residential water management, and soil moisture monitors are a viable way to achieve that.”