A small change in the way lawns and parks are groomed might improve landscape ecosystems and soil and reduce carbon dioxide in the air, all while saving money usually spent on maintenance, a recent Colorado State University study shows.
"The study shows that if lawn clippings are left on grass after it is mowed, nitrogen and carbon, two nutrients important to plants, increase within the soil. This also reduces the amount of fertilizer a landscape needs and reduces the emission of greenhouse gases from the landscape, which improves the environment," said Yaling Qian, lead researcher on the project and an assistant professor in the Department of Horticulture and Landscape Architecture.
Grass landscapes, such as that on lawns, parks and golf courses, produce a large amount of clippings every year. But clippings are often removed when turf grass is mowed, and clippings contain a major amount of nitrogen that can be reused by the landscape.
In fact, leaving clippings on landscapes and reducing typical nitrogen fertilizer applications actually improves air and soil quality, according to the study, which modeled long-term effects of leaving clippings on landscapes. The study used CENTURY, a computer-simulated ecosystem model developed by Bill Parton, Colorado State University Natural Resources Ecology Laboratory researcher, which can simulate long-term changes in soil organic carbon and nitrogen, nutrient cycling and plant production for Colorado and surrounding Great Plains states.
The study showed that the application of nitrogen fertilizer to turfgrass can be reduced over time and that the reduction should be greater when clippings are returned to the landscape. When clippings are left on the landscape as an annual practice, 25 percent less nitrogen fertilizer can be applied between the first 10 years on established turf, 33 percent between 11 and 25 years, 50 percent between 25 and 50 years, and 60 percent after 50 years. The turfgrass is not harmed by the lower amounts of fertilizer because the nitrogen from the clippings becomes available. This reduction in fertilizer also reduces the leaching of nitrates into drinking water and the emission of gaseous nitrogen into the atmosphere.
Returning the clippings to the landscape for 10 to 50 years also increases the amount of carbon stored in the soil by 11 percent to 25 percent when it is fertilized with a high amount of nitrogen, about 150 kilograms a year. Reducing nitrogen applications to 75 kilograms a year and leaving the clippings on the landscape increased carbon storage in the soil by up to 59 percent after the turf was established. Carbon dioxide emission is reduced by about 1 ton per acre per year when clippings are left on landscapes, considering the combined impacts of clipping management on soil carbon and fertilization requirements.
Results also showed that minimal – almost nonexistent – amounts of nitrogen would leach into the soil with the application of reduced amounts of fertilizer over time if clippings were left on the landscape for multiple years. Nitrogen application to grass landscapes must be reduced when clippings are left on lawns or gas emissions increase and nitrogen leaching is more probable.
Clippings have not traditionally been left on lawns because they are not considered attractive and because they may contribute to disease and thatch build-up. Leaving clippings on landscapes also reduces landfill yard waste.
The study will be published in the September-October issue of the Journal of Environmental Quality.