Nation by nation, evidence thin that boosting crop yields conserves land

Growing more in less space is good. But it may not be good enough without some help, say researchers who reviewed 35 years of data on cropland use by nation.

A cherished idea among conservationists predicts that revving up yields not only feeds an exploding population but also encourages farmers to let some of their land go wild again.

But between 1970 and 2005, rising crop yields accompanied a drop in land used for agriculture nationwide in only 34 of 161 countries, says rural sociologist Tom Rudel of Rutgers University in New Brunswick, N.J.

The majority of those successful cases had extra factors, Rudel says; land sparing often came with increased grain imports or with government policies encouraging farmers to set aside some of their fields. Rudel and a team of agriculture specialists report their findings online November 23 in Proceedings of the National Academy of Sciences.

You need a policy that assures the benefits, Rudel says. Otherwise, farmers may just increase total production while keeping the same amount of land in cultivation.

“Intensification continues to be promoted to help developing countries — I saw it mentioned in my newspaper only yesterday,” says geographer Alan Grainger of the University of Leeds in England, who was not part of the research team. “Development aid agencies invest huge sums of money in trying to make it a reality.”

The new paper’s approach is unusual, Grainger says, in that the researchers looked for effects on a global basis. Previous work has been regional or has been based on constructing models, he says. In theory, increasing yields boost supplies and prices sag. Farmers then take the less-productive land out of cultivation.

To test this idea in a broad sweep, Rudel and his colleagues turned to data from the Food and Agriculture Organization of the United Nations on crop yields and land area in cultivation for 10 crops. These diverse foodstuffs account for 57 percent of the Earth’s cultivated land and include corn, wheat, rice, soybeans, potatoes, bananas, sugarcane, coffee, cocoa and cotton.

During those years, world population grew by 74.3 percent, but cultivated land for those crops increased by only 25.7 percent, the researchers note.

In a sense, that increased farming intensity saved land that might otherwise have been converted to agriculture, comments Paul Waggoner, of the Connecticut Agricultural Experiment Station in New Haven, who has written about land-use issues.

Yet the land area devoted to agriculture still increased overall, Rudel notes. He and his colleagues did find some countries, however, in which the amount of land in cultivation decreased as a whole when yields rose. That was the case in Austria, for example, during a period when farmers were encouraged to set aside some of their fields for conservation. These lands can benefit the ecosystem by reducing erosion, providing wildlife habitat and sequestering carbon.

Data from the FAO are neither uniform nor perfect, Rudel acknowledges. The land use data were collected using methods that ranged from satellite images to the collective opinion of local experts. “If we were to wait around for the data of our dreams, who knows when that would be,” he says.

In the same issue of the journal, Grainger publishes a plea for an international system of global environmental observatories using satellite remote sensing to improve information on land use and land cover.