With concerns mounting over the environmental effects from our love of manicured lawns, Karl Guillard, professor in the Department of Plant Science and Landscape Architecture, developed a research project that examines turf as an ornamental crop with environmental assets.
In a five-year project funded through the Storrs Agricultural Experiment Station and the New England Regional Turfgrass Foundation, Guillard is investigating the potential for turfgrass to capture carbon from the atmosphere and sequester it in the soil organic matter.
“We have a lot of lawn in Connecticut,” Guillard says. “Our objective was to look at common lawn practices that have the greatest potential to sequester carbon. We are looking at this because, until recently, it wasn’t thought that short-cut lawns and turf areas such as golf courses would have much of a potential to fix carbon. Grass is a tiny plant that is mowed frequently. But within the last ten years, we’ve seen pretty strong data that suggests that these grass systems have very high potential for fixing carbon, equal to conservation reserve systems of perennial grasses. That was pretty surprising.”
Carbon dioxide levels have been increasing over the past thirty to forty years, which may account for some of the changes in our weather patterns. In Connecticut, the most common sources of atmospheric carbon are derived from the burning of fossil fuels for heating and transportation.
During photosynthesis, plants take in carbon as carbon dioxide and fix the carbon into their structural (leaves, stems, roots, etc.) and non-structural (sugars and other metabolites) components. In perennial grass ecosystems, a large portion of that carbon ends up in the soil organic matter because of their large fibrous root systems.
The majority of lawn grasses in Connecticut are perennials containing large root masses that hold carbon in various forms, from active carbon that is used by organisms such as soil bacteria and fungi, nematodes, worms and beetles, to more inactive or stable forms, such as humus, that remain stable for years. To maintain a functional soil ecosystem, there needs to be a balance of active to stable carbon. When lawns are managed correctly, the potential for removing carbon from the atmosphere and into the soil organic matter could have a significant beneficial ecological impact.
Some of the management factors that promote an environmentally healthy lawn include mowing higher, returning clippings rather than bagging and choosing grass species with deeper root systems that require less water. Guillard wants to identify methods that will maximize any benefits from turfgrass.
The project includes 360 plots sowed with four common grass species: Kentucky bluegrass, perennial ryegrass, tall fescue and fine fescue. Other factors being tested are mowing height (two, three and four inches), fertilizer application and mulch mowing or bag mowing. Each year the team takes 720 samples across two different soil depths and tests for carbon and nitrogen content. Graduate students as well as undergraduate students assist with soil sampling.
The goal is to determine which grass species have the greatest ability to accumulate soil carbon and how other factors affect the optimal amount of carbon that can be sequestered in the soil. For instance, the higher a grass is mowed, the larger the root system, which increases the soil capacity for accumulating carbon.
I am a true believer that every little bit counts,” remarks Guillard. “If we can look at making a difference in identifying which combination of practices can maximize our carbon sequestering potentials, by all means, let’s do that.”
In another project that began in 2007, Guillard is examining the use of organic fertilizer on lawns. While organic management of turf is becoming widely accepted, it doesn’t mean that organic fertilizer in excess is benign.
Guillard planted turf plots with Kentucky bluegrass and tall fescue. His team is comparing the effects of twenty-three different rates of compost fertilizing toward the goal of assessing fertilizer application rates that produce a commercially acceptable lawn while still protecting the environment.
In organic management, how much is enough? Different types of fertilizers release nitrogen at different rates. Once a critical level is reached, the grass will not show any further color or quality benefits, and there is an increased risk of nitrogen leaching into groundwater.
“I am interested in finding out if we can take an objective soil sample measurement for organic maintenance systems, and then come up with compost or organic fertilizer recommendations that maintain an optimum level,” Guillard says. “By applying additional fertilizer when it is unnecessary, it creates a system overload where over time, excess nitrogen and phosphorus could run off or leach into our water systems.”
Soil samples are being tested in two ways that differ from a typical soil nutrient test. The first, the Solvita Soil CO2-Burst Test Kit, which measures the breakdown capacity of soil organic matter by microorganisms, was originally designed to determine if compost is ready for plant use. When there is a high level of carbon in a soil, it stimulates microbial activity, which increases the potential for soil to release nitrogen. Guillard thinks this test has the potential to measure organic matter breakdown in a turf soil. The second test is the Solvita Soil Labile Amino Nitrogen test kit (SLAN), which measures the active nitrogen in soil organic matter.
The goal of this study is to find a mathematical model for predicting soil nitrogen response and categorize a turf site and its response to nitrogen by measurements from the two soil test kits. This will help guide application recommendations to ensure that enough nitrogen is present for optimum growth and quality and to prevent excessive application of nitrogen that can damage ecosystems and waterways.
“These commercially available test kits could provide a general guideline for applying fertilizer by determining whether the soil shows a low, moderate or high response to additional fertilizer,” Guillard explains.
Guillard is quick to give credit to his graduate and undergraduate students who assist with the thousands of soil samples involved in these studies. “My current right hand man in this project is my master’s student, David Moore,” he says. “He’s been a terrific student and has taken on the responsibility for both of these projects.” Before Moore, MS student Patrick McIntosh assisted in the projects. MS student Kelsey Brennan recently joined the team, and every summer Guillard employs an undergraduate student as well.
The results of these projects should identify those lawn practices that optimize soil carbon sequestration, and to determine how much organic fertilizer is needed at any lawn site. The long-term benefits of both will assist in protecting water quality and to help mitigate the effects of climate change.
“The project has been quite exciting and interesting,” he says. “We hope this information will be useful to professional lawn care companies and groundskeepers. We encourage them to incorporate soil monitoring as part of their maintenance services.”