Nuts and Bolts of Cleaning Water

By Danier Looker –
February 21, 2015
Any farmer who doesn’t think that managing nitrogen fertilizer is a complex challenge would have been convinced after spending a day at the Iowa Soybean Association (ISA) Research Conference in Ames, Iowa, Thursday. Besides looking at the results from the group’s on-farm replicated strip trials to help growers earn more from soybean and corn crops, the group also showcased its environmental research that  evaluates the best ways to reduce nitrates in Iowa’s streams and rivers.

A pending lawsuit by the Des Moines Water Works against drainage districts in three northern Iowa Counties may have been an unspoken incentive that drew about 550 farmers and researchers to the meeting at Iowa State University. Instead of legal strategy, the conference emphasized innovation and voluntary programs, including collaboration between water utilities and farmers such as the new USDA partnership program getting started between Cedar Rapids and farmers in the middle Cedar River watershed.

“What’s the best way to stave off regulation? It’s to show progress in water quality,” said Sean McMahon, Executive Director of the Iowa Agriculture Alliance, a group funded by ISA, the Iowa Corn Growers Association and the Iowa Pork Producers Association.

McMahon pointed out that the potential lawsuit from Des Moines isn’t the only pressure on farmers. Other litigation is pending as well as state efforts to reduce the farm fertilizer that accounts for almost half of the nutrients that cause hypoxia, known as the dead zone, in the Gulf of Mexico every year. 

Hypoxia in the Gulf isn’t unique. McMahon said there are more than 150 dead zones in the planet’s oceans, places where decaying algae starves the water of the oxygen needed by fish and other sea life. 

“Unfortunately, agriculture is the leading contributor to a majority of them,” McMahon said. 

Between 1960 and 2000, global use of nitrogen by farmers increased 800%, and phosphorous use rose 300%. The United States is a contrast in efficiency. According to statistics from the Fertilizer Institute, nitrogen use in the United States dropped 4% between 1980 and 2010, while corn production rose 87%, nearly doubling the efficiency of that fertilizer.

Yet, as several speakers pointed out Thursday, more efficient use of fertilizer alone won’t be enough to reach the goals of the voluntary Iowa Nutrient Reduction Strategy that started in 2013. The plan is among the first in a multi-state effort to shrink the Gulf dead zone. It seeks to lower the amount of nitrogen and phosphorous heading downstream from Iowa by 45%. Agriculture will have to come up with 41% of that reduction in nitrates reaching waterways.

Another step in reducing nitrates in streams, just getting started, is finding ways to remove some of the nitrogen with edge-of-field technology. One method, around since 2008, is the bioreactor. It’s a pit filled with wood chips. Water from drainage tile flows through the reactor, where anaerobic bacteria metabolize nitrates into atmospheric nitrogen.


Keegan Kult, ISA’s environmental projects manager, said bioreactors are just one of several edge-of-field technologies that his group has been evaluating. They typically work for a 30-acre to 100-acre field and require six-inch to 10-inch tile lines. The pit is usually about 100 feet long by 15 feet wide, filled with about a semi-load and a half of wood chips, a carbon source that the anaerobic bacteria feed upon. The chips are also a big part of the typical $8,000 to $12,000 cost of a bioreactor. And they’re estimated to last about 15 years.

At that point, if a farmer doesn’t want to spend more to recharge the reactor with new chips, it can be left in the ground without affecting drainage tile flow, Kult said.

The effectiveness of bioreactors varies a lot, according to ISA testing. Kult said that they remove about 25% of the nitrates leaving a field in tile lines and Michelle Soupir, an Iowa State University agricultural engineer who is also doing research with bioreactors  puts the range at 30% to 50% in a good year. But, like most things in agriculture, weather can reduce the effectiveness. Bioreactors are designed to divert excess water after heavy rainfall, so as much as 80% of water in tile lines can remain untreated.

And in the spring, when the ground is colder, the microbes aren’t as active, either and remove less nitrogen, said Soupir, who describes bioreactors as being at “kind of the Model T stage” of development. 

Kult said other technologies may prove more cost effective, including saturated buffers, which send water from drainage tiles through existing buffer strips along streams, which need to be at least 30 feet wide. 

Farmers don’t benefit directly from removing nitrates with edge-of-field technology, but some see it as an important part of making the state’s voluntary nutrient management strategy work.

Rob Stout, who farms in Washington County in southeast, Iowa, installed a bioreactor last year and saw a phenomenal 97% reduction in nitrates leaving a 65-acre field. 

The bioreactor cost about $14,000, he said. He was able to get half of that covered by a conservation cost share grant, “so it’s $7,000 out of my pocket, but the results are phenomenal and I’m putting out clean water,” Stout said.

Stout is a veteran no-tiller who six years ago began experimenting with cover crops on six acres. Today he seeds about 600 acres to cover  crops, he said.

Stout was part of a farmer panel at Thursday’s meeting who nearly all agreed that farmers will need to see some economic benefits to make water quality practices widespread.

Dean Sponheim, who farms near Mason City in northern, Iowa, describes himself as “an accidental environmentalist.” He started strip cropping to deal with soil compaction and germination issues in heavy clay soils, but later saw many environmental benefits as well as the lowered fuel and labor costs. The machinery he bought was too costly for his small farm, so Sponheim also got into custom work for neighboring farmers.

Sponheim also cautioned farmers against trying to make big changes on their own. “If you’re really serious about doing it, talk to somebody. Don’t wast a lot of time trying to figure it out,” he said.