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Crops of influence

Can the right winter cover crops reduce nitrate runoff into tile drainage systems? Based on research conducted by the University of Illinois’ Department of Crop Sciences, the answer is a definite ‘yes’. And it is possible to earn money from this crop as well.

That’s the takeaway from research conducted by the Department of Crop Sciences since 2016. Over the past seven years, the department has assessed the ability of winter cover crops to reduce nitrate runoff at its Dudley Smith Initiative Farm. It is a 228-acre farm in Christian County, Illinois that was donated to the University as a research site by Dudley Smith Jr. in 1993. This nitrate runoff reduction research has proven that “certain winter cover crops can reduce the amount of nitrate that gets into tile drainage below ground,” says Dr. Laura Christianson. She took part in this research as an associate professor in the Department of Crop Sciences. “The right ones can also pay for themselves.”

“To achieve this reduction, you need a cover crop that overwinters, which means it starts to grow again in the spring,” explains Christianson. “That’s why one of the most common cover crops that we recommend for reducing nitrate runoff is cereal rye, because it grows in the fall. You plant it after harvest, and it grows in the fall. This cereal rye then goes dormant over the winter, but then it starts growing again when spring arrives. In doing so, the cereal rye takes up some of the nitrogen in the soil and holds onto it — thus keeping these nitrates out of the tile drainage system. The question is, can other cover crops do the same job, while also being saleable?”

Research and results
To answer this question, the Department of Crop Sciences laid out 16 individually drained two-acre plots at the Dudley Smith Initiative Farm. “Within each plot there are three lateral tile lines that are spaced 60 feet apart,” says Christianson. “We’ve designed the system to drain about three eighths of an inch of water per day, which is a pretty standard drainage coefficient for Illinois fields. As a result, these 16 individually drained plots allow us to monitor the amount of nutrients in the drainage water in the tile pipes underneath each of them.”

Laura Christianson, center, in the field at the Dudley Smith Initiative Farm.

Again, the purpose of this experiment was not just to verify that winter cover crops can reduce nitrate in drainage, but also to determine which crops can do this work profitably as well as effectively. “At the Dudley Smith Farm, we want to answer questions about how other cover crops influence the amount of nitrate that gets into tile drainage, because all cover crops are not the same,” says Christianson. “This is why we divided the 16 plots into four treatment areas.”

The first treatment area was a control in which researchers did not plant a cover crop; just corn one year and soybeans the next with nothing in-between. This provided a baseline of nitrate runoff levels that the other areas could be assessed against.

“The second treatment area is where we’re doing corn one year and soybeans the next, with cereal rye being planted each fall after harvest,” explains Christianson. “The third treatment area on the Dudley Smith Initiative farm is where “we’re doing something a little different in our choice of cover crop. Usually this mixture involves clover. For instance, this past winter we did kale and Belansa clover. But I’ll be honest: The clover treatments haven’t germinated very well, and so we’ve had some trouble with that treatment.”

The fourth four-plot section is Christianson’s favorite treatment area, and one that farmers should pay attention to. “Last year, rather than a classical cover crop, we planted winter wheat and then double cropped those plots with soybeans ,” she says. “The winter wheat serves the same function as cereal rye: You plant the winter wheat after harvest in the fall. It goes dormant during the winter and starts to grow again in the spring. Then you harvest that winter wheat and sell it, before planting the soybeans. This means that your cover crop is also a cash crop.”

The best part? Based on their measurements of water within the tile drainage systems, University of Illinois researchers confirmed that cereal rye reduces the amount of nitrogen sent downstream by 30 to 35 percent when used as a winter cover crop. Better yet, “We saw a very similar response from winter wheat in terms of the amount of nitrogen sent downstream,” says Christianson. “This is really good news because winter wheat can be sold whereas cereal rye isn’t a cash crop.”

Implications for farmers
The University of Illinois’ research into nitrate runoff reduction into tile drains has proven that winter cover crops can make a difference, and that the right crop choice can also make money. For farmers, this is one of those serendipitous occasions where protecting the environment also protects their income.

This being said, results may vary from farm to farm, depending on their actual soil and tile drainage conditions. As well, “even when we’re doing cover crops for research at the Dudley Smith Initiative Farm, we don’t always have them come up perfectly,” says Christianson “We don’t always have them germinate as well as we would like. We don’t always get the biomass and the good stands of cover crops that we know are necessary to have a really significant water quality benefit.”

As a result, she advises farmers to adopt a range of options for reducing nitrate runoff, rather than relying solely on winter wheat as a cover crop. “It’s important to be realistic about the fact that it can be a challenge to grow cover crops to reduce the amount of nitrogen we send downstream,” she says. “So keeping your mind open to other conservation drainage practices is really important. I’m talking about practices like constructed wetlands, wood chip bioreactors and saturated buffers. There are more conservation-oriented water drainage practices than just our in-field practices. Cover crops are an important practice, but they’re not the only practice.”