WE KNOW TURF: Eco Articles

Carbon Containment

The impacts of turfgrass on our climate
by Patrick White

With the amount of publicity global warming and climate change are receiving, we've been inundated with a log list of things that produce CO2 and which therefore are bad for the environment: SUVs, coal plants, the use of private jets by sanctimonious celebrities. What we haven't heard much about are things that actually capture CO2 and rid it from the atmosphere. One of those beneficial agents, it turns out, may be turfgrass.

Ronald Follett, a soil scientist with the USDA's Agricultural Research Service, and Yaling Qian, associate professor of turfgrass science and management at Colorado State University, have been studying the ability of turfgrass to capture CO2 during photosynthesis and then "sequester" some of that carbon in the soil. Their work has focused on examining soil records at 16 golf courses in and around Denver, Colo., and though still in its early stages, the results are proving quite revealing. Notably, they've found that each acre of greens and fairways sequesters nearly one ton of carbon every year, removing it from the atmosphere and essentially trapping it in the soil.

"It's a dynamic process. Through the process of photosynthesis, turfgrass synthesizes some of the carbon in the atmosphere, and some of that gets into the soil and becomes soil organic matter," explains Qian. "Some will decompose and then be released--but with carbon sequestration, there is a net gain: there is more carbon put into the soil than is released."

Golf courses, in particular, have proven to be a good choice for study says Follett. "These are highly managed ecosystems. They are watered, they've got extra nutrients supplied and you've got a grass that's a solid stand that usually has a good root system, which is important to sequestering carbon."

Their focus of golf courses has also been helpful because superintendents tend to keep detailed records of soils and maintenance practices, providing the long-term perspective needed to study carbon sequestration.

"It's important to understand the definition of carbon sequestration," emphasizes Follett. "It's a long-term storage; it's not like you just grow some grass on top of the soil and that sequesters carbon because you mow it. It has to actually get incorporated into the soil organic matter--the key is for it to be long-term. Some of the carbon in the belowground root material of grasses does become incorporated into soil organic matter as sequestered carbon. A tree that grows for 100 years before being cut down, which then might be made into furniture, is long-term sequestration. A crop of aboveground corn that's harvested every year does not produce carbon sequestration. A golf course of maintained turfgrass will be there for a long time, and it's actually incorporating the carbon into the soil."

Along those same lines, any study of the ability of turfgrass to sequester carbon in the soil requires an extended effort. "It takes time to start accumulating carbon, several years at least," says Follett. There also may be variations in the rate of carbon sequestration as turfgrass stands age. Their research shows that "a rapid increase in carbon sequestration occurs the first 25 to 30 years after the turfgrass is established." Using soil and turfgrass records kept by superintendents, the study determined that after 31 years in fairways and 45 years in greens, the rate of carbon sequestration slowed dramatically.

However, for all those years, the carbon will have been sequestered in the soil, away from the atmosphere where it could be harmful. Over time, it will also have been transformed into forms that pose less danger to the atmosphere. "The turfgrass takes in the carbon and puts it into its roots. There, as the roots release it, the microbes are processing it into more recalcitrant products that are harder to be lost. Of course, the microbes are expiring and releasing some of it, but as the carbon works through a number of biochemical processes it becomes more and more inert," says Follett, attempting to explain the complex process.

Turfgrass is not unique among plants in sequestering carbon. "But you're dealing with a totally different system with trees," explains Follett. "Trees have different mechanisms for sequestering carbon. With turfgrasses, you're really working with a species that has a very fibrous root system, and there's a lot of carbon in that. And, weedy species of plants often have individual root systems that don't put as much carbon in, nor are they maintained in a solid stand the way turfgrass is."

Unlike agricultural crops, where the soil is frequently tilled or otherwise disturbed, golf courses and other maintained areas, such as ball fields and lawns, tend to see little soil disturbance. "I attended a research seminar where they talked about how not tilling soil increases carbon sequestration. That got me thinking that turfgrass is almost never tilled, so it must have a high carbon sequestration rate," recalls Qian of her first initial interest in this line of research.

"If you scrape the soil off in construction or something like that, and stockpile that soil in a pile, it will begin loosing the carbon until something is planted on it, and even then it might still be losing it," says Follett. "Under bare soil there's going to be an active biological population of microbes and fungus that are going to be expiring and releasing that carbon into the atmosphere."

Turfgrass that's grown in a dense, solid stand provides a good way to keep that carbon from being released. "Though they're concentrated mostly near the surface, turfgrass produces a lot of roots," says Qian, "and there are also rhizomes, as well as the clippings that fall down. So, that all contributes to the carbon buildup and sequestration."

Of course, gauging the net reduction in atmospheric CO2 provided by turfgrass also means examining factors such as the CO2 produced by the mowers and other equipment required to manage and maintain the grass, and research on these subjects will be important to providing answers regarding the total impact of turfgrass on CO2 emissions.

As the amount of maintained turfgrass in this country increases (it's currently estimated at 2 percent of the total land surface), there is likely to be more research focused on the effects (pro and con) that turfgrass has on the climate. For example, a recent research project at the University of California Irvine Arboretum was designed to measure "the exchange of gases between the grass and the air." Researchers there found that "turfgrass may contribute to greenhouse warming rather than mitigate it, as turfgrass removes carbon but emits nitrous oxide, a potent greenhouse gas, because of high levels of fertilization." That study also found that as temperatures rise, turfgrass removes less carbon from the atmosphere.

At Kansas State University, Assistant Professor Dale Bremer is studying the issue of nitrous oxide emissions from turfgrass. "Although there is much less N2O in the atmosphere than carbon dioxide, N2O has more than 300 times the warming power of carbon dioxide," Bremer explained in a recent article for the Kansas Turfgrass Foundation's newsletter. Any living plant fertilized with nitrogen can emit N2O, but little research has been done specifically on the emissions of turfgrass as compared to, say, agricultural crops, Bremer says.

"Does this mean turfgrass is bad or that this will cause problems for the turf industry? Certainly there are groups who already dislike the turf industry who may cite this as another bad thing about turfgrass. However, turfgrass is not 'lighting a fire' to the atmosphere, nor is the turfgrass industry likely to come under attack any more than agriculture... Turf certainly has valuable aesthetic and, in many cases, environmental values, for example, turf is used in buffer strips on stream banks to reduce pesticide and fertilizer runoff into surface water. Thus, turfgrass is not as environmentally unfriendly as some would like to say," explains Bremer.

Shedding light on the turfgrass emissions of N2O, as he hopes to do, shouldn't make the turf industry a target, he says, but rather should help to reveal specific best management practices, such as not overwatering or over-fertilizing, that can help turfgrass managers extract the maximum environmental benefits from turfgrass with the fewest environmental costs.

Likewise, as they continue their research on the ability of turfgrass to sequester CO2, Follett and Qian hope to discover the affects that various maintenance practices have on that process. "The main objective now is to study the amount of carbon sequestration among different types of turfgrasses, and different management practices," says Qian.

That research examines out-of-play, less maintained areas on golf courses; rough areas that receive moderate maintenance and mowing; and fairways that receive frequent mowing, watering and fertilization. "We're also looking at greens, both California greens and USGA greens," adds Follett of the most intensely managed parts of golf courses. The results of this research won't be available for some time, as the researchers work to take into account the many variables involved in order to produce accurate results that can be helpful to turfgrass managers.

Follett and Qian say they hope their research helps provide an answer to one part of the puzzle in understanding and controlling greenhouse gases. "I think if we're going to address the issue of CO2 in the atmosphere, there will have to be a whole suite of activities that address it. There's not going to be one magic bullet. We have to look at what's sequestered under croplands, under turf systems, under forests, and put all the pieces together," says Follett. "But, I think the turfgrass is a particularly important part of the equation, because there is so much acreage in turfgrass in this country, and it's growing. And, with the right information and management practices, it's likely that the amount of carbon that turfgrass sequesters could be increased."

Patrick White is a freelance writer and editor who is always on the lookout for interesting and unusual stories. He can be reached at pwhitevt@aol.com.

This article originally appeared in the August 2007 issue of Turf magazine and has been reprinted with permission. For more information, call 800-422-7147 or visit www.turfmagazine.com.

Photo by Patrick White.

Photo caption: Research being conducted on golf courses is helping to demonstrate the ability of turfgrass to sequester carbon and keep it out of the atmosphere.