Could the Grass Be Greener?
Lawn turf is America's biggest crop--and a mixed bag for the environment
From green shoots in the North to the first mosquitoes in the East and a profusion of ill-advised fashion choices everywhere, all of the classic signs of spring are in place. But the clearest harbinger of all is so common you could almost miss it unless you're trying to sleep in on a Saturday morning: the insistent droning of America's 50 million or so lawnmowers.
For most Americans, the home turf is a modest plot of green. But add those front and back yards together with all of the nation's sports fields, golf courses, town squares, and other grassy plots, and a surprising thing happens. All told, according to a report to be published later this year in the journal Environmental Management, some 40 million acres of America are covered in lawns, making turf grass our largest irrigated crop. That's more than enough to have a significant impact on the nation's environment, but despite growing concerns about excessive watering and the use of lawn chemicals, that impact might not be all bad.
Using census data, satellite images, and aerial photographs, the researchers estimated the total area of turf grass in the 48 contiguous states. Then, says lead author Cristina Milesi, they used computer simulations to estimate the environmental impact of those lawns under different levels of management. Assuming that all 40 million acres of lawn are watered and fertilized at recommended levels, says Milesi, now a researcher at NASA, Americans pour as much as 238 gallons of water per person, per day onto lawns during the growing season. But lush lawns also turn out to be a "sink" for carbon dioxide, pulling the greenhouse gas out of the atmosphere as they grow. The effect is more pronounced when grass clippings are left to decompose in place, boosting growth by providing nitrogen--though offset by the 800 million gallons of gas burned in lawnmowers every year. All told, says Milesi, "the 2 percent of the U.S. land surface that is covered in lawns could account for about 5 percent of the . . . carbon dioxide" absorbed by all plants.
Overkill? Still, that positive effect isn't likely to change environmentalists' minds about the danger posed by so many perfect lawns. Farmers and golf course managers have an economic incentive to conserve resources like water, fertilizers, and pesticides, Milesi notes. "But for the single homeowner," she says, "lawn care is usually not a big part of the budget, so there's a temptation to always do a little more." Outdoor watering accounts for more than half of municipal water use in most areas, and homeowners often apply fertilizers and pesticides to their lawns at many times the recommended levels.
In arid regions, there are usually strict regulations on lawn watering. Fertilizers, which can seep into waterways, have been blamed for excess growth of algae and aquatic plants in lakes and coastal areas. And, citing the potential danger to human health and wildlife, a consortium of environmental groups is pushing large retailers to carry less harmful alternatives to the tens of millions of pounds of insecticides and weedkillers used on private lawns every year.