The Nitrate Runoff Problem in Iowa, and its Costs

As Des Moines Water Works pursues a lawsuit against upstream county drainage districts, it outlines the costs of and desired improvements to its nitrogen removal equipment:

Des Moines Water Works says it spent $540,000 this winter — and another $500,000 in 2013 — to run its nitrate removal facility.

Altogether, nitrate levels at the utility intake exceeded federal drinking limits 1,636 days between 1995 to 2014 — 24 percent of the time. The agency has run the nitrate removal facility 673 days over those 19 years. That's about 10 percent of the time.

The utility says it's looking to invest up to $183 million over the next five years to replace the existing denitrification plant, "due to its age and the limited capacity."

The agency anticipates it will need to build a nitrate removal plant with a "50 million gallon per day capacity," five times the existing plant's capacity, according to its lawsuit over high nitrate levels.

Bill Stowe, the CEO of Des Moines Water Works, said the utility's denitrification capacity is likely closer to 15 million gallons per day, depending on the water temperature and nitrate levels. The utility needs to build a plant to handle growth over the next 20 to 25 years and to meet stricter nitrate removal standards, he said.

He also anticipates federal drinking water standards could be cut by half in the future.

The Des Moines Register has a number of stories about nitrate runoff from Iowa farms.  The main sources:

Two factors have given rise to Iowa's high nitrate levels, research shows:
• Drainage tiles, which help make about 12 million acres of Iowa land farmable, enable nitrogen that's both applied and in the soil organically to move much more quickly into Iowa rivers and streams.
• Massive row-cropping, which has put roughly two-thirds of Iowa land into farm production, also is elevating nitrate concentration in the state's waterways, say Schilling and others. And the loss of perennial crops such as alfalfa in many farmers' rotation plays a role in those rising levels.
In essence, the very elements that have made Iowa farmers the most productive in the world are responsible for elevating nitrate levels in the state's waterways....
Much of Iowa's nitrogen — and nitrates — are in the soil organically.
Iowa has about 10,000 pounds of organic nitrogen per acre, according to Iowa State University professors Matt Helmers and Michael Castellano. "To get a sense of scale, a farmer might apply 150 to 200 pounds of nitrogen per acre to a corn crop," said Castellano, an assistant professor of agronomy.
Each year, about 30 pounds of nitrogen per acre is lost, much of it from organic matter that's already in the soil, say Castellano and Helmers. Studies show about the same amount of nitrogen is lost regardless of whether farmers grow corn or soybeans, which requires no nitrogen application.
"There's no statistical difference," Castellano said.
Nitrates occur when Iowa's rich soils get warm and wet, and microbes convert nitrogen — both that farmers apply and what's available organically — into nitrates, which plants use to grow.
Problems occur, though, when there are no plants in the fields to soak up the nitrates — particularly in the spring and the fall — allowing them to seep into waterways, said Castellano and Helmers, an agricultural biosystems engineer.
It's why leaders have pressed farmers to adopt conservation practices such as cover crops. Cereal rye and other crops can help soak up nitrates before Iowa's massive corn and soybean crops are too young to do it in the spring — or ready to be harvested in the fall, the ISU professors say.

 It's hard for this Ohio farmer to imagine soil so rich in organic matter that large amounts of nitrates leach out all winter.  So do Iowa farmers still apply a lot of anhydrous ammonia in the fall and winter for the next year's corn crop, or have they moved to more nitrogen application by sidedressing during the growing season?