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Too much fertilizer has consequences

Laurie DrinkwaterLaurie Drinkwater is one of a group of 17 authors of Nutrient Imbalances in Agricultural Development in the current issue of Science (324:5934).

According to a Cornell Chronicle article, Midwest farmers overfertilized their corn in the ’70s, but they increased yields and synthetic nitrogen fertilizer use efficiency by the mid-’90s.

Yet, the environmental consequences of using inorganic fertilizers have persisted, 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 in the summer. 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,” said 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.”

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