As long as Iowa farmers lead the nation in corn production, they will be among the leading contributors of nitrogen fertilizer to the dead zone in the Gulf of Mexico.
Peak corn production, upon which much of Iowa depends, itself depends upon nitrogen fertilizer, the pollutant responsible for the dead zone, and upon the key conveyor of the pollutant to the gulf, agricultural drainage tile.
Illinois and Iowa are the leading contributors of nitrogen to the dead zone — a 6,400-square-mile area with oxygen concentrations too low to support life.
In 2008, the Mississippi River Watershed Task Force created the Gulf Hypoxia Action Plan, calling for a reduction of the size of the dead zone by 2015. This would require a reduction of nitrogen runoff by 45 percent, a goal that most environmentalists and policymakers recognize as impossible.
In part because of the rapidly increasing price of nitrogen fertilizer — now about $750 per ton, enough for 10 to 12 acres of corn — farmers have developed techniques to use it more efficiently.
The leaching of nitrogen from the soil into drain tile is a fact of life, though, said Linn County farmer Curt Zingula.
“Nitrate leaching is really the only downside of tile,” said Zingula, who farms about 1,500 acres in northeast Linn County.
Without tile, crop yields would be substantially lower and soil erosion and stream siltation would be worse, said Zingula, who is helping to form an organization to manage flooding and water quality on Indian Creek.
Without tile, the process of denitrification — which releases nitrous oxide, a greenhouse gas, into the atmosphere — also would be worse, he said.
To ensure maximum crop utilization of expensive fertilizers, Zingula in 1999 began using variable-rate application — which incorporates grid soil testing, computers and global positioning system technology — to apply precise amounts in specific field locations.
Like many other farmers, Zingula also strives to apply nitrogen just before and during the growing season, when plants can most fully use it.
It takes about a pound of nitrogen fertilizer to make a bushel of corn, and Iowa farmers raised about 2.3 billion bushels of corn last year. That means that at least 1.15 million tons of nitrogen, in the form of livestock manure and commercial fertilizer, were applied on 13.7 million acres — or about 38 percent of the state’s surface area.
Some of it gets away, mostly through agricultural drain tiles emptying into ditches and streams that are part of the vast Mississippi River watershed, eventually contributing to the dead zone.
The Iowa Environmental Council and other environmental groups have sued the Environmental Protection Agency, contending that the EPA has failed to enforce regulations to reduce nitrogen and phosphorus, resulting in the failure of states to develop effective water-quality policies.
Although manure application is regulated, chemical fertilizers are not, leaving only the voluntary efforts of farmers to control fertilizer usage.
When fertilizer was cheap, the rule of thumb was “plant thick, pour on the fertilizer and pray for rain,” said Charles City farmer Mark Kuhn.
That has changed since the run-up of fertilizer prices, but farmers still tend to err on the side of high yields, said Kuhn, a member of the Floyd County Board of Supervisors and a leader of the seven-county Upper Cedar River Watershed Management Improvement Authority.
Farmers are aware of their contribution to the dead zone, said Kuhn, who believes the watershed organization can encourage the use of voluntary, incentive-based practices that will reduce nitrogen and sediment pollution in the upper Cedar.
Conscientious fertilizer management is a key component of Brandon farmer Dick Sloan’s commitment to “tread lightly on the Earth.”
Taking into consideration the price of corn and the price of fertilizer, he calculates the amount of fertilizer that would yield the optimum return on his investment.
“There is a point beyond which you could apply more fertilizer and grow more corn, but you would also be wasting fertilizer and money,” said Sloan, president of the Lime Creek Watershed Improvement Association,
Sloan supplements his commercial fertilizer with the manure of 1,000 hogs, which he injects to a depth of 6 inches. Lab testing pinpoints the manure’s nutrient value, enabling him to precisely calculate the amount of commercial fertilizer he needs to attain his yield objectives.
Testing of the nitrogen content of his cornstalks after harvest helps ensure Sloan is not wasting fertilizer.
Constructed wetlands at tile outlets effectively filter much of the escaped nitrogen before it enters streams, but government funds to aid wetlands construction are in short supply. A new project, the Iowa Wetland Landscape Systems Initiative, would expand the wetlands filtration concept to larger areas.
Pilot projects of the so-called “Iowa Plan” include a completed site in Pocahontas County and six other sites that are in the hearing process. If monitoring at the seven sites demonstrates a substantial reduction in nutrients, more such systems could be built across the state.