Farmers in the Mississippi River Basin - an area that makes up 55% of U.S. agricultural land - could face a mandatory 20% cut in nitrogen fertilizer use. That's one recommendation from a federal task force as a way to reduce hypoxia in the Gulf of Mexico.

Hypoxia is a shortage of oxygen. Some environmentalists believe hypoxia is caused by "over- enrichment" from nutrients, such as nitrogen and phosphorus, flowing into the Gulf from the Mississippi River and its tributaries. The ove r-enrichment can create excessive algae, which can kill marine life by sapping the oxygen supply.

The hypoxic zone reached a modern high - 7,000+ square miles - in 1999. Yet Gulf fisheries have not suffered economic loss.

A federally appointed task force recently studied the hypoxia issue. It declared that, "Scientific investigations over the last several decades indicate overwhelmingly that hypoxia in the Gulf is caused primarily by excess nutrients delivered to those waters from the Mississippi-Atchafalaya River Basin, in combination with stratification of Gulf waters."

The task force says the amount of fertilizer nitrogen entering the Mississippi River drainage basin has increased dramatically. And the principal sources, it claims, are river basins that drain agricultural lands in southern Minnesota, Iowa, Illinois, Indiana and Ohio.

But some Midwestern political leaders and scientists charge the task force with using poor science. They also contend the feds are pushing one theory as the primary cause of hypoxia. They don't deny that fertilizer can play a role, but maintain that far more is involved.

Illinois Governor George Ryan notes that, "While the relationship between fertilizer use in the Midwest and Gulf hypoxia remains scientifically unproved, some of the recommended responses could have serious economic consequences for Midwestern farmers."

Derek Winstanley, chief of the Illinois State Water Survey, and other scientists point out that total nitrogen in the lower Mississippi River is not increasing. In fact, they say it was about the same in 1980-1996 as in 1900, and is much lower than in 1950.

They also claim there is no consistent relationship between use of nitrogen fertilizer and the concentration of nitrate in the Mississippi River Basin. And they say there's no significant relationship between the annual flux of nitrogen from the Mississippi-Atchafalaya River Basin and the surface area of the hypoxic zone.

The scientists maintain that the task force has not adequately evaluated the natural forces - such as rainfall and other nutrient sources and processes - that create hypoxia. They point out that millions of square miles of the world's oceans, including along the coast from the U.S.-Canada border to Chile, are naturally hypoxic.

"It's my opinion that the water quality in the Mississippi River Basin has improved in the last 20 years," says Cliff Snyder, Midsouth director for the Potash & Phosphate Institute.

He points out that nitrogen fertilizer use has stayed basically static since 1985, while the hypoxic area in the Gulf has ranged up and down from practically nothing to 7,000 square miles. That indicates other factors are involved.

"We may still have some problems in certain areas with nitrogen loss," he says. "But we don't need blanket action."

Snyder says the authority to monitor and regulate the waters should reside with state and local bodies. "Most states already are asking farmers to voluntarily apply best-management programs, and they're asking the federal government to give the programs time to work."

Farmer-researcher Marion Calmer, Alpha, IL, has long participated in hypoxia discussions.

"I've seen evidence that nutrient loading in the water can increase hypoxia, but I haven't seen good evidence that nitrogen fertilizer is the main source," says Calmer. "A mandatory 20% across-the-board cut in nitrogen use could be devastating to farmers and to food production."

He says one way to reduce nitrogen loss is to apply it in the spring. "Timing of application is very important in minimizing leaching or denitrification," he notes.

"Our on-farm research shows that 150 lbs of nitrogen fertilizer applied in the spring, plus available N in the soil, can produce 175- to 225-bu corn in a corn-soybean rotation," Calmer reports.

President Clinton this spring is scheduled to submit a plan to Congress for reducing the Gulf hypoxia zone. Farm groups are urging producers to ask their congressional representatives to make certain any future legislation is based on sound science rather than on emotion.