A wash? Growing corn has become much more energy efficient--a key aspect of sustainability--but U.S. farmers are planting more of it.

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Farming Strides Toward Sustainability

The production of four major crops now requires significantly less land, water, and energy per bushel or bale than it did 20 years ago, marking progress toward sustainable agriculture, according to a new report to be released later today at the American Farm Bureau Federation annual meeting in San Antonio, Texas. The report comes from an unusual collaboration of agribusinesses, farmer organizations, and conservation groups.

Agriculture is facing enormous challenges. The world population is expected to exceed 9 billion by 2050, so farmers will need to ramp up production to feed everyone. The question is how to do that while reducing the already large environmental impact. Agriculture is a major contributor to greenhouse gas emissions, and fertilizer that washes off fields is creating dead zones where marine life can't survive in lakes, estuaries, and gulfs. Farm fields and pasture take up 40% of Earth's total land surface and consume 70% of fresh water used worldwide--and may have to expand overall, leaving even less room and resources for nature. Moreover, depletion or loss of soil from destructive farming practices, such as excessive plowing, threatens the business itself.

Not surprisingly, farmers and environmentalists haven't been on the best of terms. "There hasn't been a lot of understanding between the two," says Kenneth Cassman of the University of Nebraska, Lincoln. "People in agriculture have felt persecuted for producing for the safest, cheapest food in the history of mankind." Meanwhile, some green groups are deeply suspicious of large agribusiness and its high-tech tools, including genetically modified crops. Last year, for example, an ambitious effort designed to assess the role of science in agriculture and development was derailed by disputes (Science, 14 March 2008, p. 1474).

That's why Cassman and others are heartened by the development of the consortium that produced the report, run by the nonprofit The Keystone Center in Keystone, Colorado. "To have a scientific, credible conversation between agribusiness and the environmental community is really great," says Jonathan Foley, a global change scientist at the University of Minnesota, St. Paul, who studies the impact of agriculture. "This is a watershed moment."

The report analyzes the impact of growing four crops--corn, soy, wheat, and cotton, which account for 70% of farmed acres in the Unites States--from 1987 to 2007. One key finding is that the amount of land required to grow a certain amount of food has fallen. Because of yield gains, for example, it now takes 37% less land to grow a bushel of corn than it did in 1987. In addition, the rate of soil loss per amount of grain or cotton grown has declined between 30% and 70%. This is due mainly to the adoption of no-till farming, in which the fields are not plowed multiple times for weed control. Less plowing means less soil blows or washes away.

The analysis, led by agronomist Stewart Ramsey of the consulting firm Global Insight, also finds that the amount of energy spent on farming has fallen by 40% to 60%, probably because farmers who plant genetically modified crops are driving tractors less frequently to spray pesticides and herbicides. Irrigated water use dropped by 20% to 50%, the report found, and carbon emissions fell by about 30%. Wheat was the only crop of the four surveyed that did not post big gains in efficiency. More water is being used, and an increase in application of nitrogen fertilizers has meant an increase in energy use and climate impacts per bushel.

Still, taken as a whole, "we've seen dramatic increases in efficiency," says Marty Matlock, an ecological engineer at the University of Arkansas, Fayetteville, who coordinated comments from 17 peer-reviewers. One reason efficiency is important, notes participant Michael Reuter of The Nature Conservancy in Arlington, Virginia, is that growing more food per hectare may mean less destruction of rainforest or other habitat.

Tom Tomich of the University of California, Davis, notes that the increases in efficiency per unit output, however, do not necessarily mean improvements in sustainability. The overall picture matters: Despite the improved efficiency of corn production, it still requires more energy and fertilizer than soybeans do. So when farmers plant corn instead of soybean--as they have since the expansion of biofuel demand--the overall environmental impact increases. "We're very far away from a truly sustainable agriculture," Foley says.

The consortium is now working on metrics for water quality and biodiversity--which are significant environmental impacts and much tougher to measure--and hopes to eventually expand to the health and social impacts of agriculture. Eventually, it will create outreach programs to promote more environmentally benign farming. As a first step, the consortium will launch a Web site for farmers to estimate the efficiency of their own operations.