Greenscape Gardens Green Blog

SPACING OUT ON TURFGRASS

Satellite data shows that in terms of surface area, turfgrass is the largest irrigated crop in the United States. There are three times more acres of lawn in the U.S. than irrigated corn.

The study used satellite data on impervious surfaces to estimate how much of the country is covered by bermuda-
grass, St. Augustine, fescue and other turfgrass. The study defined lawns as residential and commercial landscapes, golf courses and other turf-covered areas. Cristina Milesi of the NASA Ames Research Center’s ecological forecasting group led the study. “Even conservatively,” Milesi says, “I estimate there are three times more acres of lawns in the U.S. than irrigated corn.”

This means lawns—including residential and commercial lawns, golf courses, etc—can be considered the single largest irrigated crop in America in terms of surface area, covering about 128,000 square kilometers in all. Her next task was to figure out some of the ecological impacts of this crop of lawns Americans are cultivating.

Ecological Impact of Lawns

Recognizing that different people and businesses treat their lawns differently, she had a computer simulate the effect on the water cycle and carbon cycle of different lawn manage-
ment techniques. The variables the models tested included watering a fixed amount (including rainfall) versus watering according to weather and evaporation rates, adding different amounts of fertilizer, and leaving the clippings on the lawn after mowing or bagging them up.

Some of the results weren’t surprising, explains Milesi. The model confirmed that if people watered according to a fixed amount, about 2.5 centimeters (1 inch) per week minus rainfall, then lawns in rainier places, such as Lincoln Park, Michigan, wouldn’t need any irrigation at all, while Yuma, Arizona, would need the full 2.5 centimeters of irrigation each week.

“If people watered according to what the meteorology indicated, factoring in temperature and humidity, for example, then it would improve irrigation efficiency—use less water—in the Southeast, where humidity is high. But in the West, there is so much sun and humidity is so low that plants can evaporate a lot more than 1 inch of water a week.” In the West, if people watered according to evaporation rates, the model predicts they would need to water nearly 200 centimeters per year.

To learn more about the turfgrass study visit http://earthobservatory.nasa.gov/Study/Lawn/lawn.html