Across the globe, fertilizing crops in the extreme

CORNELL (US)—Fertilizer use varies dramatically around the world, from inadequate to excessive, with both extremes having substantial human and environmental costs, a new report shows.

The study by Laurie Drinkwater, associate professor of horticulture at Cornell University, compares the nutrient balances of the three very different agricultural systems that grow maize as a major grain.

Farms in northern China use six times more nitrogen fertilizer per acre than farms in the midwestern United States but produce just about the same yield of corn. Meanwhile, farms in western Kenya uses one-thirteenth what the U.S. farms use, and corn yields remain paltry.

Farms in the Midwest, the article notes, over fertilized their crops through the 1970s, but by the mid-1990s, better farming methods increased corn yields and at the same time improved the efficiency of synthetic nitrogen fertilizer use.

By 2005 corn yields in the Midwest and China were about the same, but Chinese farmers were using about 525 pounds of nitrogen fertilizer per acre compared with 83 pounds in the Midwest. Farms in northern China generated nearly 23 times the amount of excess nitrogen than those in the Midwest.

The environmental consequences of using inorganic fertilizers have persisted in the United States, says Drinkwater, an agroecologist who studies the Mississippi River Basin. Nitrogen runoff from farms has drained into the basin and then into the Gulf of Mexico for years, creating huge “dead zones,” including one that grows to an area the size of New Jersey during the summer months. The dead zones are due to the runoff nutrients that fuel massive algal blooms, which, in turn, consume most of the water’s oxygen, making it uninhabitable to fish.

In addition, ammonia from fertilized cropland has become a major source of air pollution, while emissions of nitrous oxide form a potent greenhouse gas.

“As we see from the situation in the Mississippi River Basin, reducing the nitrogen fertilizer surplus does not resolve the environmental consequences of using these fertilizers,” says Drinkwater. “We know we need to apply more of our basic understanding of biogeochemical processes to succeed in that; we need to think about diversifying rotations and using practices that solve some of the root causes of nutrient loss from agriculture.”

The study, published in the June 19 issue of the journal Science, is based on discussions at the Aspen Global Change Institute and is supported by NASA, the William and Flora Hewlett Foundation, and the David and Lucille Packard Foundation, and at a meeting of the International Nitrogen Initiative sponsored by the Scientific Committee on Problems of the Environment. P.M. Vitousek of Stanford University is the study’s lead author.

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