Northwest Iowa research explores nitrate runoff from farm fields

SIOUX CENTER, Iowa | Matt Schuiteman farms land around all but two of the city of Sioux Center's 12 shallow wells.

Worried about the threat the nitrogen-based fertilizer applied to his corn acres posed to the underground aquifer, the Northwest Iowa farmer agreed five years ago to take part in a comprehensive study aimed at controlling the runoff, while still allowing him to grow crops on the valuable soil.

"The nitrates in the city wells were coming up a bit," Schuiteman said. "We wanted to make sure we could keep farming. We didn't want to see a lot of land going to (the Conservation Reserve Program) if we could help it."

As commodity prices have soared to historic highs in recent years, the federal CRP has become less attractive economically to farmers around the country.

At the same time, public health officials have expressed growing concerns about runoff of nitrogen, not only from fertilizer but also from livestock manure spread on fields.

The Environmental Protection Agency requires nitrates in drinking water be kept at less than 10 milligrams per liter. Levels above that can be deadly to infants six months or younger because the chemical can reduce the amount of oxygen carried in their blood.

The Sioux Center research project, which brought together the city, state and federal environmental agencies and Dordt College, examined five alternative cropping systems on a 40-acre tract of Schuiteman's land, above a bank of shallow wells that provide more than 50 percent of the drinking water for Sioux Center, pop. 7,210.

"The idea was to use perennial crops and cover crops to keep the nitrogen in the upper layers of the soil and available for next season, and apply just what the crops need when they need it," Dordt environmental studies professor Robb De Hann said.

De Haan was awarded a $90,000 grant for the research, which was funded by the Leopold Center for Sustainable Agriculture on the campus of Iowa State University and the Iowa Department of Natural Resources' Source water Protection Program for Targeted Community Water Supplies. Findings of the study were presented at a public meeting last month in Sioux Center.

The alternative cropping systems the researchers designed for standard farm equipment ranged from continuous corn on corn with a winter rye cover crop to perennial grass. The latter is common for wellheads but generally a low-income choice for farmers.

Three other systems used various rotations of corn, soybeans, wheat, oats, alfalfa and red clover. No commercial nitrogen was applied to the perennial grass or alfalfa crops.

After collecting six-foot-deep soil samples each fall, the researchers used the data to construct nitrate profiles for each plot and track nitrate movement over time.

As expected, the findings showed the continuous corn with rye left high levels of residual nitrate in the top two feet of soil.

The grass or hay acres averaged five-fold fewer residuals for every year and at every depth, proving to be the most effective system for reducing nitrate escape into local water supplies. However, wheat with a soybean and corn rotation performed better than continuous corn with rye.

Adding a tap-rooted legume, such as red clover or alfalfa, to corn dramatically lowered residual nitrate levels, De Haan said.

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