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Iowa farmers may find some cover

BY ALISON CASSITY | JULY 13, 2015 5:00 AM

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Statewide, Iowa has battled high nitrate levels for the past several years.

Now, as Des Moines begins a lawsuit against surrounding counties, potentially dangerous nitrate levels in drinking water have become an issue of interest for many environmental and farming organizations.

“High nitrate levels can be dangerous to select groups, primarily pregnant women and infants fewer than 6 months old,” said Diane Moles, the executive director of the Iowa Department of Natural Resources’ Water Supply Engineering Section.

According to a recent report released by Natural Resources, 11 public water sources across Iowa exceed federal nitrate levels and approximately 260 Iowa cities and towns are highly susceptible to contamination from nitrate pollution. Iowa City is not among them.

The Environmental Protection Agency has set the current maximum nitrate containment levels to 10 mg/L, and according to a 2014 Iowa City report, the city’s level averages 5.8 mg/L.

The spike in nitrate levels across the state can be traced to Iowa’s corn and soybean fields, said Susan Heathcote, the water program director at the Iowa Environmental Council.

“The biggest source of nitrates is primarily coming from our intensive agricultural cropland in Iowa,” she said. “Sixty-five percent of our land is used for corn or soybean crops.”

These plants, she said, are called “annual crops” — they are planted in early spring and harvested in the fall.

“We call it a really leaky system,” Heathcote said. “There’s a lot of organic matter that has lots of nitrogen and phosphorous in it, and then we add chemical fertilizers, which also contain nitrates.”

The biggest problem, though, is not the fertilizer, she said. Instead, it’s the fields that go four to five months without anything growing in them to absorb the nitrates from the soil.

“There’s nothing there taking [nitrates] up, no roots in the ground, and the fields are also very vulnerable to soil erosion during this time,” Heathcote said. “This is where we get what we call subsurface leaching into the water source, which then becomes pollution.”

However, Sarah Carlson, a Midwest cover crops research coordinator at Practical Farmers of Iowa, said the nitrate spike is not completely a man-made issue. Naturally occurring nitrates can be abundant in certain types of soil, she said.

“Yes, we need to watch how much nitrogen we’re adding to the soil, but fertilizer isn’t the main problem,” Carlson said. “In a good central Iowa soil, a drained landscape, we can have 10,000 pounds of nitrate in the soil. Farmers only apply maximum 200 pounds each year.”

The solution may be as simple as planting cover crops, which would grow during the typically empty months, she said.

“We really need to cover up the winter window,” Carlson said. “[With cover crops], the nitrates are much more stable.”

Using cover crops to absorb nitrates and prevent soil erosion can make all the difference when it comes to affecting the water supply, Heathcote said.

“We’re trying to persuade more farmers to plant a cover crop like cereal rye,” she said. “It holds the soil in place during the fall and early spring and absorbs the nitrogen and phosphorous up into the plant.”

Organizations such as the Practical Farmers of Iowa are helping in this effort by hosting field days in which farmers can learn how to plant a cover crop and what the benefits are, Carlson said.

She said more and more farmers are planting cover crops, especially because of the availability of federal, state, and county funding.

“These field days have been really successful because it’s farmers teaching farmers,” she said.

“They’re going to be really honest about what works and what doesn’t, which is why it’s been so successful in Iowa.”


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