Nitrogen Nightmare: Could This Simple Idea Curb Farm Runoff Contamination?

How close crops come to a country stream, like those that meander through countless acres of American farmland, may not seem like a major factor when it comes to everything from tap water to your next shrimp cocktail. However, new science finds that laying just a thin strip of grass or other native plants between chemically fertilized lands and the heartland's free-flowing waters could have a significant impact on the drinking water of millions, not to mention wildlife in the Gulf of Mexico's growing dead zone.

According to a new report from the Environmental Working Group, leaving just a 35-foot buffer between fields of corn or soy and neighboring streams could reduce nitrogen runoff by 7 percent and phosphorus by 18 percent. In 2013 the state passed the Iowa Nutrient Reduction Strategy, which set voluntary goals for reducing “non-point pollution”—mainly farm runoff—targeting a 41 percent drop in the nitrogen load running into waterways, and a 29 percent reduction in phosphorus. Plants need both nutrients to grow, and together they are the primary components of chemical fertilizers.

Aerial view with suggested buffer. (Photo: Courtesy
National Agricultural Imagery Program)

The report comes on the tails of a controversial lawsuit filed by the Des Moines Water Works, the state capital’s water utility, which is suing three upstream counties over the excessive levels of nitrogen in the Raccoon River. According to EWG, only 0.12 percent of farmland dedicated to growing corn and soy would need to be replanted with grasses in order to implement 50-foot buffers in the five representative counties looked at in the report. That’s just 1,500 acres across all five counties.

Some 500,000 Iowans rely on the Raccoon for their drinking water, and in order to make it potable when the nitrogen load spikes, it cost $4,000 a day to treat it. Des Moines’ lawsuit may set up a new battle between rural and city residents, but this is by no means a new problem. According to another EWG report on Iowa river and stream pollution, the state Water Quality Index found water quality was considered “poor” or “very poor” at more than half of the 98 sites monitored.

As reporting from NPR has made clear, controlling runoff isn’t simply a means of using less chemical fertilizer. In the summer months, when Iowa’s low, rolling fields are planted with more corn and soy than nearly any other state, the plants suck up nutrients and water alike, minimizing any runoff. The problem lies partly in winter’s snow-covered fallow fields. When spring rolls around and everything melts, that water picks up the remaining nutrients in the soil and washes them into creeks, the drinking water supply, and eventually, the Gulf of Mexico, leaving thousands of miles of damage in their wake. “The way to fix this is we need to have something growing from October to May," Sarah Carlson, a scientist who works for a group called Practical Farmers of Iowa, told NPR.

Carlson floats rye—which is planted in the fall, sits dormant in the winter, and matures in time for a spring harvest—as a cover crop that could help further mitigate the issue. Others have suggested that deep-rooted daikon radishes planted along the edges of farmland could help break up bare, compacted soil, helping to mitigate both runoff and erosion.

But what’s particularly interesting about buffers as a solution is that they could help eke out a tiny bit more space for native plants and the wildlife they support—like the milkweed that monarch butterflies rely on for their very existence. Out of Iowa’s some 36 million acres of land, more than 30 million are cultivated, making Iowa second only to gigantic California in terms of ag production.

Not only does that leave little wild space where nostalgic Iowans can see the profuse blooms of native prairie, it’s also deteriorating an ecology that farmers benefit from. From the loss of topsoil to reduced pollinator populations, every acre that’s plowed under and planted in corn and soy impacts the natural resources Iowa’s farming tradition was built on. Thankfully, bringing it back on an even larger scale than a small streamside buffer here and there could help improve it.

At least that’s the idea behind STRIPS—science-based trails of row crops integrated with prairie strips—which could help mitigate the myriad problems faced by farmers and urban Iowans alike, according to researchers at Iowa State University.

“Our hypothesis was that if you put a little bit of perennials—a little bit of prairie—in the right place, you get these disproportionate benefits,” Lisa Schulte Moore, an ISU researcher, told New York Times columnist Mark Bittman last November. “That is, without taking much land out of production, you get a lot of environmental benefit.”

As Bittman writes, by converting 10 percent of a field to native prairie—nearly 10 times the amount of cropland EWG proposes in its stream-buffer study—“soil loss can be reduced by up to 95 percent, nutrient loss by 80 to 90 percent, and water runoff by 44 percent.”

Stream buffers may be a low-impact solution; winter rye crops a practical one. But if we want to address Iowa’s environmental and ecological problems in a major way—and improve everything from local drinking water, the environmental impact of the country’s major commodity crops, and the Gulf’s dead zone as a result—it’s going to take something bigger. And letting more of the state go wild looks like a very good place to start.