Arizona's parched desert is home to the University of Arizona's Karsten Turfgrass Research Facility – where scientists study every means possible to grow heat- and salt-tolerant recreational turf using less and less reclaimed water.
Turfgrass is considered a commodity. Each year the golf industry alone contributes more than $3.4 million to Arizona's economy, provides nearly 20,000 jobs and attracts thousands of tourists, according to the state's Golf Industry Association.
Yet population growth in arid Arizona is exponentially increasing demand for scarce water resources. Arizona was the second fastest growing state in the nation between 2000 and 2009, according to the U.S. Census Bureau. As of 2010, the population totaled 6.6 million residents – more than triple the 1970 census population of 1.8 million.
Most arid municipalities require the use of effluent to water golf courses and other recreational turf – which presents growing challenges because of its high salinity.
UA scientist Paul Brown has researched how to grow suitable turfgrass with less water for more than 20 years. He's a biometeorologist in the department of soil, water and environmental science in the College of Agriculture and Life Sciences, and also a UA Cooperative Extension specialist.
Pushing limits of water tolerance
"We know turf can survive on less than optimal amounts of water. We try to find the minimum requirements to give acceptable visual quality and performance," Brown said.
Research by Brown and his UA colleagues demonstrated that certain turf grasses can survive on 20, even 25 percent, less water than optimal – as long as accumulated salts are leached from the soil.
The 7.5-acre Karsten Turfgrass Research Facility at the Campus Agricultural Center includes five putting greens built to U.S. Golf Association specifications, two 4-meter-deep lysimeters that simulate water use of golf fairways, and a computer-controlled irrigation system linked to an on-site weather station. The prime irrigation source is tertiary effluent from the City of Tucson.
"Lysimeters are basically big buckets of soil that sit on a scale with plant materials growing on them," Brown said. "By measuring changes in weight during the day, we can measure amount of water going in with irrigation and precipitation – and measure the amount of water lost through evaporation, which is referred to as evapotranspiration, or ET."
This ET data is then related to a meteorological estimate of evaporative demand known as reference ET and used in conjunction with data from weather stations to accurately predict turfgrass water use. Reference ET is a critical input variable for most scientifically based irrigation-scheduling systems.
Linking weather stations to irrigation systems
Brown developed and oversees the Arizona Meteorological Network, or AZMET, a near-real-time agricultural weather information system with 28 stations that provide reference ET. The AZMET website is an industry resource and provides turf water use reports for Phoenix and Tucson.
"On average, our website handles about 50 requests a day related to turf water use in the Phoenix area alone," Brown said. There are about 290 hits daily for weather data collected by Phoenix-area stations.
Brown and his colleagues make regular industry presentations, offer an annual turfgrass course and produce turfgrass bulletins, "which are basically research summaries directed to the lay user, rather than to a scientific journal," Brown said.
Superintendent of Paradise Valley Country Club Rob Collins sought Brown's expertise in 2006.
"We had an issue with exceeding our state water allotment. We turned to industry professionals, irrigation manufacturers, our peers – anywhere we could find good information," Collins said.
"Ultimately Paul Brown was the best source of field-driven information. He'd been testing golf irrigation uniformity and knew it backwards and forwards. Clearly his knowledge is scientific – something as simple as how much grass do you have to remove in order to save a certain amount of water?"
The club converted 11 acres of turf to natural desert landscaping.
"It worked. It was effective. We met our goals. Paul's involvement with our club has been immeasurably beneficial," Collins said.
Identifying salt-tolerant grasses
Initial funding for the turfgrass facility came from Karsten Manufacturing (Ping) in the early 1990s. The City of Phoenix is among the backers of AZMET. In 2006 the Golf Course Superintendents Association of America supported a deficit irrigation project to test drought, heat and salt tolerance of certain grasses.
That project is led by James Walworth, specialist in the UA department of soil, water and environmental science, working with David Kopec, a turfgrass specialist in the UA School of Plant Sciences.
Plots of seven types of salt-tolerant grasses – four bermudas and three paspalums – are grown with descending amounts of water.
"Ultimately we want to better understand how much you can cheat on irrigation water," Walworth said. "We want to determine how the water stress affects quality."
Remarkably, the irrigation research indicated plants could manage with 20 to 25 percent less reclaimed water while still maintaining an acceptable turf surface.
"The amount you have to apply depends on what you're demanding of the grass. A city park requires one quality of grass. A high-end golf course takes a bit better quality. A football stadium needs an even better quality."
Providing students research opportunities
While a master's degree candidate at the UA, Jaime Bañuelos did much of the field work and became the lead author of the deficit irrigation report published in Agronomy Journal. "The bottom line – bermuda grasses are better able to handle severe deficit irrigation," he wrote.
But you have to manage the salts. Accumulated salts can slow water absorption and burn the turf. Too much sodium can actually block absorption, causing water to run off and pool elsewhere.
For irrigated turfs, "it is essential to leach salts out of the soil with storm events. Rainwater is nearly pure water. It’s very effective at leaching salts out of the soil," Brown said. "One of our concerns is it's been quite dry over the past 10 to 12 years. We've not had the winter rains we're used to having. Drought is antagonizing the problem.
"These water issues and irrigation uses are not going to go away. We've made pretty good progress. I think it's helped to put the scientific data down on the table. We need to move forward and determine what grasses we'd like to have, what we can live with and how best to manage them."