Australian scientists have found that grassy sports fields used for soccer, cricket, and baseball can release a potent greenhouse gas into the environment. A yearlong study at La Trobe University in Melbourne, Vic., suggests that mowing, fertilizing, and applying herbicides to turfgrass sports fields contributes to the release of large amounts of nitrous oxide.
“This study is another indication that urbanization has complex impacts on our environment,” said Amy Townsend-Small, a biogeochemist who was not involved with the research. “Even though most cities are working toward increasing their amount of green space, this doesn’t always help meet climate goals.”
A Greenhouse Gas That Eats Away at the Ozone Layer
Nitrous oxide is the third most emitted greenhouse gas, after carbon dioxide and methane. Although it makes up only 7% of greenhouse gas emissions in the United States, it has 265 times the global warming capacity of carbon dioxide. The gas is also the largest source of ozone-depleting substances from humans.
In soil, nitrous oxide is emitted by microbes digesting chemical compounds for energy. Although the process is natural, humans have cultivated soil conditions that encourage more gas production. Agriculture emits the most nitrous oxide of any sector.
As the world urbanizes, scientists are studying how nitrous oxide emissions are concentrated outside the agricultural realm. A better understanding of how sports fields contribute to emissions could help mitigate those emissions. Although the problem is relatively small, turf’s footprint may be large. In one study by Cristina Milesi of the NASA Ames Research Center, it was calculated that turfgrass covers an area 3 times larger than any other irrigated crop in the United States.
Emissions Similar to High-Intensity Farming
In the latest study, David Riches, a research fellow at La Trobe, and his colleagues installed instruments to measure nitrous oxide and methane on campus fields used for soccer and cricket.
“What we found was we got really quite high emissions in the sports field soils which were comparable to [those] of the high-intensity vegetable production systems we’ve previously been working in,” said Riches. The team monitored conditions for 213 days from autumn to spring on one sports field and intermittently on two others.
Applying herbicide to the field caused the largest jump in nitrous oxide emissions. Herbicide likely prohibits new growth and frees up more soil nitrogen for hungry microbes, researchers said.
Aerating, fertilizing, and watering for the oncoming sports season also increased nitrous oxide emissions. Watering decreases the microbes’ access to oxygen, making them produce more nitrous oxide.
Notably, the three sports fields’ emissions were 2.5 times higher than those of an unused lawn nearby. Nitrous oxide averaged around 38 grams of nitrogen per hectare per day at the continuously monitored sports field (data at the other two were intermittent), versus about 9 grams of nitrogen per hectare per day at the lawn.
“You do get these peaks of high emissions in the sports field, which you just don’t get in the lawn,” Riches said.
More Careful Management Could Cut Emissions
One way to reduce emissions could be to water only when a field needs it, Riches said. Another idea might be to dial back the amount of fertilizer and use a slow-release or nitrogen-inhibiting product.
The study was published in Science of the Total Environment in March.
Extrapolating to the rest of Australia, Riches figures that grass playing fields alone do not have a significant impact on greenhouse gas emissions. But the effect could be greater if lawns, parks, gardens, turf farms, roadside vegetation, and other intensively managed green spaces are shown to emit as much as sports fields.
“If you look at all the intensively managed in total, then it might start to become more significant,” Riches said. “Then you might want to do something to mitigate it when you can.”
—Jenessa Duncombe (@jrdscience), Staff Writer
This story is a part of Covering Climate Now’s week of coverage focused on “Living Through the Climate Emergency.” Covering Climate Now is a global journalism collaboration committed to strengthening coverage of the climate story.
Duncombe, J. (2021), Turf’s dirty little secret, Eos, 102, https://doi.org/10.1029/2021EO156939. Published on 14 April 2021.
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