University researchers are continuing a study on irrigation systems to increase water efficiency, according to the project’s leader, assistant professor of biological and agricultural engineering Garry Grabow.

Their current research has shown that Raleigh’s two-day-a-week watering restriction is acceptable for keeping up a lawn, Rod Huffman, an associate professor of biological and agricultural engineering, said.

“So far it doesn’t look like watering twice a week is any problem,” he said. ?Researchers began the study, which Grabow said was funded from the Center for Turfgrass Environmental Research and Education, in 2006, when they buried water-measuring sensors and laid sod in a site off Lake Wheeler Road.

Grabow said they were evaluating different irrigation systems by comparing water use and turf quality.

The system that most households have now, Huffman said, is one set to a timer, which sets a time each day to water, regardless of the conditions.

“There are more intelligent technologies and we’re looking at several of those,” he said.

One of the more “intelligent” systems involves evapotranspiration, by measuring the amount of water lost through transpiration and evaporation and estimating how much water is needed to restore the grass, Huffman said.

There are also systems that water only when the water levels have reached a certain low, according to Huffman.

“We are just trying to determine what technologies and what combinations of things seem to work best in this area so we can minimize the amount of water that’s used and still maintain acceptable turf quality,” he said.

Another system uses a satellite to download weather data, and apply water according to that, but Grabow said it used more water than was necessary.

Some of the sensor-based systems can be used as add-ons to a current irrigation system, he said, and are more affordable for homeowners than the satellite system.

The first year of study had higher-than-average temperatures and drought conditions, and Grabow said the researchers want another year of research before they draw conclusions.

“It was a year that would stress and test out any technology,” Grabow said.

But watering twice a week is “probably something we can live with,” he said, and representatives of Raleigh, Cary and Durham have expressed interest in their findings.

Jack Colby, associate vice chancellor for facilities operations, said the University has adhered to Raleigh’s irrigation restrictions, and wants to expand its use of more advanced irrigation technology.

About 20 percent of the University’s grounds are irrigated with the help of a wireless system that monitors soil moisture, “to irrigate only when necessary,” according to Colby.

Bobby Vick, a senior in biological and agricultural engineering who collected data in the study, said it is important that these systems be useful to the average homeowner.

“We want to save enough water so that it will save the homeowner some money,” he said.