Can the world's existing farmlands provide enough crops to satisfy the hunger of the nine billion people—up from seven billion currently—that demographers predict will be living on the planet by the mid-21st century? Or will more and more forests and other ecosystems have to be cleared to feed all the extra mouths? A new study, published in Nature on August 30, suggests that increasing deforestation could be avoided provided farmers made better use of water and nutrients on land currently under cultivation around the globe. (Scientific American is part of Nature Publishing Group.)

The central premise of the new analysis is that intensifying agriculture where it already exists is the key to preserving a balance between farming and forests. To do that, the researchers from McGill University in Montreal and the University of Minnesota (U.M.) analyzed the so-called yield gap. That's the difference between what the highest yielding farm or area within a given region can produce—for example, corn—compared with what the average yield is. The difference between this best-practice farm and the average farm is the yield gap.

The researchers then employed national and regional agricultural data from outfits such as the Food and Agriculture Organization of the United Nations and the International Fertilizer Industry Association to determine the root causes of these yield gaps. Simply by improving fertilizer application and irrigation, the researchers find that global yields of corn, wheat and rice—the three main staple crops—could be increased by 64 percent, 71 percent and 47 percent, respectively.

"We are not claiming to diagnose the exact management practices needed on any particular plot of land," explains research fellow Nathan Mueller, who led the study from the U.M.'s Institute on the Environment, because local factors such as soils and weather can play an important role. Instead, the goal is to identify what practices might help close yield gaps at the regional or even global level and highlight those areas most in need of intervention.

That list includes the U.S. Great Plains and China, where more fertilizer is used than is strictly necessary. For example, American farmers apply so much fertilizer on Midwestern corn fields that much of it ends up running off, ending up in the Mississippi River and, ultimately, reaching the Gulf of Mexico. There the copious fertilizer fuels a bloom of algae and other microscopic plants that then die. Microbes that consume the dead plants also use all the oxygen available in surrounding waters, creating a vast "dead zone" that is devoid of sea life—an unfortunate side effect of the demand for more maize.

Lessening fertilizer use in the U.S. and China would free up nutrients to be applied to fields in eastern Europe and western Africa with no detriment to American or Chinese people. As it stands, the researchers estimate that some 11 million metric tons of nitrogen fertilizer and five million metric tons of phosphate could be saved annually at present without diminishing current yields. Those savings then could be applied to underachieving areas.

The finding suggests that more than enough food could be produced on existing agricultural lands, even without including advanced farming techniques, soil restoration or improved crop varieties. But, as the authors note: "closing yield gaps may not always be desirable or practical in the short term," because of the inability to make profits from such yield increases; local land ownership issues; limits on sustainable water use; or simple poverty and the inability to undertake, for example, irrigation projects.

"We have to move from identifying potential interventions to determining the social, economic, institutional and policy levers that can make them happen," argues co-author and ecologist Jonathan Foley of U.M.

Already, the world's farmers produce more than enough calories to feed every man, woman and child on the planet—more than 3,000 calories per individual, or some 22 trillion calories annually. Of course, that's not what ends up on everyone's plate, thanks to inequalities in distribution and waste—whether during harvest, storage or 3someone's refrigerator. Then there is the corruption that keeps food from getting to the poorest people in India, for example. If there is a food crisis, it is a political problem as much as, if not more than, an agricultural challenge. "We already have enough crop production to feed our current population, and yet nearly a billion go hungry every day," Mueller notes. "Reducing food waste and smarter diets are extremely important levers" to reduce the demand to produce ever more crops.