Greener Ways to Greener Lawns

During the record-setting 2007-08 drought in North Carolina, when the governor called water conservation everyone’s patriotic duty, a brown lawn was a badge of honor instead of a neighborhood blight. But even before that drought began, NC State researchers were studying ways to use less water in outdoor irrigation, which could make green yards honorable during future dry spells.

Dr. Garry Grabow, an assistant professor and extension specialist in the Department of Biological and Agricultural Engineering (BAE), said he couldn’t have timed a study of lawn watering any better than to have it coincide with a historic drought. Grabow and Drs. Rod Huffman of BAE and Dan Bowman and Grady Miller of the Department of Crop Science received a three-year grant from NC State’s Center for Turfgrass Environmental Research & Education to examine how well controllers on automatic sprinkler systems save water while maintaining a healthy lawn.

“There’s anecdotal evidence that people put 50 to 100 percent too much water on their lawns,” Grabow said. “You just can’t afford to do that, especially during a drought.”

The researchers set up 40 plots of tall fescue amid an array of automatic sprinkler heads at a Lake Wheeler Road field lab. Some of the squares were watered using the on-off timers found on most residential sprinkler systems. Buried sensors that measure soil moisture helped determine when to water other plots.

A third group of plots had controllers that watered based on downloaded weather data and calculations of how much water the grass lost through evaporation and transpiration. Some plots in each group were limited to once or twice weekly watering to mimic municipal restrictions. Grabow says systems based on soil moisture hold the most potential for balancing conservation with a green lawn.

“It’s not just the total amount of water you put on your lawn that matters,” he said. “It’s also when you do it.”

Researchers also learned lawns could easily survive under restrictions that allow watering only twice a week.

If Bowman and Dr. Ron Qu, a molecular biologist in Crop Science, are successful in their research, the type of grass on your lawn could become another critical factor. They are developing transgenic tall fescue that is more drought-tolerant than existing varieties.

Qu has experimented with tall fescue for several years, and Bowman noticed that one of Qu’s transgenic lines seemed to last a day or two longer without water before wilting. The same grass line bounced back after not being watered for 14 or 15 weeks and going dormant.

“Some of the grass that went dormant was gone for good,” Bowman said. “Some recovered slowly, but this line came back very strong.

The drought tolerance came from a gene Qu inserted into the grass from Arabidopsis, a plant in the mustard family so widely used in genetic studies that Bowman calls it “the fruit fly of the plant world.” The two researchers are studying how the gene works in conjunction with other modifications to make tall fescue hardier against drought.

But the experiments are limited for now to Qu’s lab and Bowman’s greenhouse—the U.S. Department of Agriculture limits field studies of transgenic plants to reduce the chance of pollen spreading—meaning their new variety of tall fescue won’t be in anyone’s yard for some time.

Recycled wastewater is a more near-term solution for outdoor irrigation needs, said Dr. Tom Rufty, a crop science physiologist recently named the first Bayer CropScience Professor of Sustainable Development. Known as reuse water or gray water, treated effluent is already used at dozens of homes and businesses in Cary and will eventually be piped to the Lonnie Poole Golf Course on Centennial Campus, which will open this summer.

“As long as people use water in their daily lives,” Rufty said, “effluent will be an available resource.”

Designed by golf legend Arnold Palmer’s company, the Centennial Campus golf course is intended to demonstrate sustainable practices and serve as an outdoor research lab. Reuse water is one such sustainable practice, said Rufty, whose 10-year study of nitrogen losses from turfgrass showed that using treated wastewater for irrigation wouldn’t pollute streams and lakes.

Because nitrogen levels in grasses stabilize after 10 to 15 years, scientists theorized that nitrogen added after that—through fertilizer or reuse water—would move into nearby streams. Rufty says his study disproved that notion, showing the extensive microbial activity in the soil beneath mature grasses readily converts solid or liquid nitrogen into gas that escapes into the atmosphere.

Irrigating the golf course with nutrient-rich reuse water will cut in half the need to apply fertilizer, Rufty said. Overall watering will be reduced as well, he says, by the use of natural buffers, native plants, and drought-tolerant grasses in the rough.

“Using less water is part of a sustainable system,” he said. “It can be done.”

Editor’s note: Results: Research and Graduate Studies at North Carolina State University is published three times yearly by the Office of the Vice Chancellor for Research and Graduate Studies.