Last week, I attended a demonstration of a new conservation practice and learned a new word—bioreactor.
On the drive over to the event, watching the young corn rows flicker past in bright green, I thought once again how the productivity of these deep, rich Midwestern soils is based on the ability to drain them. And it’s this water leaving the land, often laden with nitrates, that is increasingly the focus of conservation programs in farm states like Iowa.
A tile line bioreactor consists of a trench filled with a carbon source, in this case wood chips. As tile line water flows through the bioreactor, microorganisms break down the nitrate and expel the substance as a gas.
The project sponsors, which included the Iowa Soybean Association, Sand County Foundation, and Agriculture’s Alliance for Clean Water, were enthusiastic about the early results for the technology. The first bioreactor in the state, installed in Greene County last August has cut nitrate concentrations by 60% to 70%, said Keegan Kult, an environmental specialist for the soybean growers group.
What’s the future for bioreactors? There are issues in designing and managing the structures. USDA is studying the funding eligibility for the practice.
The 12x100-foot bioreactor we watched being built will cost about $7,000 -- for the control structures, wood chips, fabric, and contracting work. It will treat water from a 40-acre tile pattern.
A bioreactor is a field-level practice, which can be relatively expensive compared to watershed-wide practice. A small wetlands restoration, for example, can receive drainage from a couple thousand acres, filter the water, and provide other conservation benefits.
The farmer hosting the demo project I saw is clearly conservation-minded. He’s been willing to pay for practices that are proven to benefit soil and water. His strip-till beans were covered in protective corn residue. The creek taking the water from the bioreactor demo was flanked by a 130-foot wide buffer strip.
Conservation practices can provide direct benefits, even if long term, to a farmer. But a bioreactor?
"This is a pretty progressive step for a farmer to take," Kult told me. “The bioreactor is helping the people downstream."
Driving home I followed the creek from the demo farm down to the Boone River, which shortly drains into the Des Moines River--the water supply for the city of Des Moines. Soon that demo farm’s 40 acres of drainage becomes just a drop in the bucket of an agriculturally intense watershed. There are about 9.5 million acres in the Des Moines River basin.
Bioreactors are just beginning to be put to the test, but you hope that farmers and the people downstream will find in them a new conservation tool.
Video: Bioreactor tour
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