Why the corn boom could hurt the Gulf of Mexico

Corn rows
One of the nation's largest corn crops ever is emerging from farm fields. More corn also means more fertilizer and that could be a problem for the Gulf of Mexico.
MPR Photo./Mark Steil

Ocean scientists wonder just how much of the corn boom will end up in the Gulf of Mexico. No matter how careful farmers are, some fertilizer washes into streams and rivers before it's absorbed by the plant.

Nancy Rabalais has studied the Gulf of Mexico dead zone for more than 20 years. It's an area where fertilizer and other nutrients produce a pool of oxygen-deprived water, a condition known as hypoxia.

Map of the gulf's dead zone
A "dead zone," shown in gray, occurs in the Gulf of Mexico each summer as nutrient buildup leads to drastic reductions in oxygen in bottom waters. Fish and shrimp catches virtually disappear.
Map courtesy of NASA

"We can only conclude that the hypoxia will be worse in some way," says Rabalais. "Either in duration or extent or size."

Rabalais is executive director of Louisiana University's Marine Consortium. She says last year's 6,700-square-mile dead zone hurt the fishing industry, especially shrimping. She says much of the farm fertilizer in the gulf is brought in by the Mississippi River from the Upper Midwest.

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University of Minnesota soil scientist Gyles Randall was part of the first national research team to study the dead zone in the late 1990s. He agrees this year's corn crop brings with it increased environmental risks.

"Yes, we're going to have more problems," says Randall. "The degree is how much."

There's been a lot of debate over exactly what role agriculture plays in producing the gulf's dead zone. Municipal wastewater, lawn fertilizer and even naturally occurring nutrients all contribute.

University of Minnesota soil scientist Gyles Randall has worked for about 35 years at the Southern Research and Outreach Center in Waseca.
MPR Photo/Mark Steil

However, Randall says most researchers believe farm fertilizers, especially nitrogen, are the chief culprits in producing the problem. He says Minnesota alone accounts for about 7 percent of the total nitrogen load entering the Gulf of Mexico.

"If we manage our nitrogen more crisply, and we use exactly what's needed, we can reduce those nitrate losses significantly," says Randall.

Randall says how a farmer plows can have a big impact. Done correctly, newly tilled furrows work against the slope of the land, acting as miniature water holding dams. Poorly plowed furrows are more like stream channels, multiplying the erosive impact of rainwater.

Randall says farmers should also pay close attention to when they apply fertilizer. He says research shows most fertilizer runs off in a relatively short window of time.

"Yes, we're going to have more problems. The degree is how much."

"Seventy-three percent of the water that we lose out of the tile lines was coming from April, May and June," says Randall. "Just those three months."

Another option, the simplest step, is to reduce the amount of fertilizer applied.

Southern Minnesota farmer Robert Meyer is mostly retired now, but he learned the value of cutting fertilizer use firsthand.

For the past 15 years or so, the state agriculture department has studied runoff from Meyer's fields. He found he could cut fertilizer use 25 percent and still harvest a crop equal to what a heavier dose of fertilizer produced.

Meyer says now is a good time to spread that lesson around. He says farmers are always eager to hear how they can reduce costs.

Robert Meyer owns a farm near St. Peter in southern Minnesota. The place is named "Red Top Farm."
MPR Photo/Mark Steil

"High oil prices have led to high chemical and fertilizer prices," says Meyer. "The farmer is going to find a way to adapt, or die. That's the way it's always been and the way it always will be. They're very open to ideas, I'll tell you that."

Ocean researcher Nancy Rabalais says that willingness to adapt too often is undercut by economic reality. She believes farmers need incentives to adjust.

"It's a matter of public will, and the commitment also of the government to support reasonable practices in agriculture rather than just subsidizing crops," says Rabalais.

Rabalais says the U.S. crop production system will be tested again in July. That's when a team of researchers head into the Gulf of Mexico to measure this year's dead zone.