The role of farm production
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.
High organic soil matter is “one of the reasons why we have such high production in Iowa,” Castellano said. “It’s also one of the reasons we have nitrate losses.”
For the original Des Moines Register article, click here.