Dan Charles, reporting for NPR:
Paul Jasa/University of Nebraska-Lincoln
“Here’s the bigger picture, Carlson says: During the summer, when crops are growing on those fields, they scarf up most of the soil’s available nitrate. The plants need it to grow. And as a result, during that period, there’s usually not much nitrate flowing into streams and rivers.
”Our problem is, we only grow plants for five months out of the year,” she says.
Most Midwestern farmers grow corn and soybeans, which are warm-season plants. And after they’re harvested, for seven long months, from fall until the following spring, nitrate continues to form naturally in the soil. It can be released from decaying plant roots or from microbes, “and if there’s nothing to suck it up, to scavenge it, then it’s going to move,” Carlson says.
Rainfall and melting snow will carry it downstream to Des Moines and beyond. It damages wildlife and fisheries all the way to the Gulf of Mexico. Many other rivers and estuaries suffer from similar problems.
We won’t fix this mess by using less fertilizer, Carlson says. “The way to fix this is, we need to have something growing from October to May.””
