The Lawn Is the Largest Irrigated Crop in the USA


“Each year, we drench our lawns with enough water to fill the Chesapeake Bay! That makes grass – not corn – America’s largest irrigated crop. Our nation’s lawns now cover an area larger than New York State, and, each year, we use about 2.4 million metric tons of fertilizer just to maintain them. When there is too much fertilizer on our lawns, essential nutrients are easily washed away by sprinklers and rainstorms. When these nutrients enter storm drains and water bodies, they often become one of the most harmful sources of water pollution in the United States” (source).

The following is a study from The International Society for Photogrammetry and Remote Sensing (ISPRS):

ABSTRACT: Lawns are ubiquitous in the American urban landscapes. However, little is known about their impact on the carbon and water cycles at the national level. The limited information on the total extent and spatial distribution of these ecosystems and the variability in management practices are the major factors complicating this assessment. In this study, relating turf grass area to fractional impervious surface area, it was estimated that potentially 163,812 km2 (± 35,850 km2) of land are cultivated with some form of lawn in the continental United States, an area three times larger than that of any irrigated crop. Using the Biome-BGC ecosystem process model, the growth of turf grasses was modelled for 865 sites across the 48 conterminous states under different management scenarios, including either removal or recycling of the grass clippings, different nitrogen fertilization rates and two alternative water irrigation practices. The results indicate that well-watered and fertilized turf grasses act as a carbon sink, even assuming removal and bagging of the grass clippings after mowing. The potential soil carbon accumulation that could derive from the total surface under turf (up to 25.7 Tg of C/yr with the simulated scenarios) would require up to 695 to 900 liters of water per person per day, depending on the modeled water irrigation practices, and a cost in carbon emissions due to fertilization and operation of mowing equipment ranging from 15 to 35% of the sequestration.

CONCLUSIONS: In this study we mapped the total surface of turf grasses in the continental U.S. and simulated its water use and C sequestration potential under different management practices for irrigation, fertilization and fate of the clippings. Rather than trying to accurately quantify the existing fluxes, we simulated scenarios in which the entire surface was to be managed like a well-maintained lawn, a thick green carpet of turf grasses, watered, fertilized and kept regularly mown. The accuracy of the results is therefore limited by both the uncertainty in the mapping of the total lawn area and by the simplifying assumptions made while modeling turf grasses growth. The analysis indicates that turf grasses, occupying about 2% of the surface of the continental U.S., would be the single largest irrigated crop in the country. The scenarios described in this study also indicate that a well-maintained lawn is a C sequestering system, although the positive C balance discounted for the hidden costs associated with N-fertilizer and the operation of lawn mowers comes at the expense of a very large use of water, N, and, not quantified in this study, pesticides. The model simulations have assumed a conservative amount of fertilization (a maximum of 146 kg N/ha/yr). In general the rates of N applications are similar to those used for row crops, and the current high-input choices made by consumers and professional turf managers for maintaining monocultures of turf grasses typical of many lawns and play fields comes at the risk, not analyzed here, of watershed pollution due to improper fertilization and use of pesticides. If the entire turf surface was well watered following commonly recommended schedules there would also be an enormous pressure on the U.S. water resources, especially when considering that drinking water is usually sprinkled. At the time of this writing, in most regions outdoor water use already reaches 50-75% of the total residential use. Because of demographic growth and because more and more people are moving towards the warmer regions of the country the potential exists for the amount of water used for turf grasses to increase. Beneficial effects of turf grasses, such as a carbon sequestration but also recreation, storm runoff reduction due to increased soil infiltration in occasion of intense rainfall, and removal of impurities and chemicals during percolation of the water through the root zone, could be sought by minimizing the application of fertilizers and pesticides, introduction of lower input species mixes such as clover and other so-called weeds (Bormann, 1993), on site decomposition of the grass clippings and extending the practice of irrigating with waste water rather than with drinking water.

For more on the subject, see:

  • Jenkins, V. S. (1994). The Lawn: A History of an American Obsession. Smithsonian Books. ISBN 1-56098-406-6.
  • Steinberg, T. (2006). American Green, The Obsessive Quest for the Perfect Lawn. W.W. Norton & Co. ISBN 0-393-06084-5.
  • Wasowski, Sally and Andy (2004). Requiem for a Lawnmower.

Article by Bill Norrington

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Distribution of the fractional turf grass area (%) in the conterminous U.S. (from the ISPRS article)

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There may be more acres of lawn in the U.S. than of the eight largest irrigated crops combined. Here are figures for the top four (http://scienceline.org/2011/07/lawns-vs-crops-in-the-continental-u-s/)

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Acre-feet of water used on US crops, compared to lawns. Ibid.

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Capability Brown’s landscape design at Badminton House. Lawns may have originated as grassed enclosures within early medieval settlements used for communal grazing of livestock, as distinct from fields reserved for agriculture. It was not until the 17th and 18th century, that the garden and the lawn became a place created first as walkways and social areas. They were made up of meadow plants, such as camomile, a particular favorite. In the early 17th century, the Jacobean epoch of gardening began; during this period, the closely cut “English” lawn was born. By the end of this period, the English lawn was a symbol of status of the aristocracy and gentry; it showed that the owner could afford to keep land that was not being used for a building, or for food production. (Wikipedia: Lawn)

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Before the mechanical lawnmower, the upkeep of lawns was only possible for the extremely wealthy estates and manor houses of the aristocracy. This all changed with the invention of the lawnmower by Edwin Beard Budding in 1830. It took ten more years and further innovations, including the advent of the Bessemer process for the production of the much lighter alloy steel and advances in motorization such as the drive chain, for the lawnmower to become a practical proposition. Middle-class families across the country, in imitation of aristocratic landscape gardens, began to grow finely trimmed lawns in their back gardens. From the 1860s, the cultivation of lawns, especially for sports, became a middle-class obsession in England. Pictured, a lawnmower advertisement from Ransomes. Ibid.

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More than 90 percent of UCSB’s manicured landscape is now irrigated with recycled water, which saves 19.5 million gallons of potable water annually (The UCSB Current)