Plan Now to Keep Nitrates in Check

August 28, 2012 11:18 PM
Plan Now to Keep Nitrates in Check

Nitrogen might be a management challenge this fall

Tim Hoffman believes a ground-soaking rain this fall could be a mixed blessing. On one hand, he knows his parched corn fields need moisture after enduring the worst drought in half a century. On the other hand, he worries about the nitrogen that remains in his fields, unharnessed by the drought-damaged corn crop.

"If the nitrogen converts to nitrate, it could seep into the Sangamon watershed and Lake Decatur, two valuable water resources in central Illinois," says Hoffman, who, in addition to growing corn and soybeans, serves as board chairman for the Agricultural Watershed Institute (AWI), based in Decatur, Ill.

His concerns are shared by Doug Gucker, biomass director and agronomist for AWI.

"I have this terrible fear that once we get the soil recharged, we’ll have tiles running again and the nitrate levels will spike and it’ll be all over the news," Gucker says.

One solution to the potential nitrate problem is for farmers to gate their tile, notes Ken Ferrie, Farm Journal Field Agronomist. "If feasible, install gates on the outlets so you block the tile and don’t let the water out," he says.

The downside, Ferrie says, is that few people have that option available  because older tile systems don’t have gates. He adds, "If you have too much grade on your tile, you’ll blow the tile apart and damage the drainage."

A more viable option than closing gates on tile, Ferrie says, is for farmers to plant cover crops. That is a solution Hoffman plans to implement.

Nitrogen net. "Cover crops do a good job of absorbing nitrates and preventing erosion," Hoffman says. "Besides, I’ve already paid for that nitrogen, and I’d like to find a way to use it." Earlier this season, Hoffman applied nitrogen for his corn crop in preplant and sidedress applications as usual.

Ferrie says radishes, oats and rye are three cover crops that absorb nitrates effectively.

"Last year, our rye cover crops pulled anywhere from 100 lb. to 140 lb. up into the crop," he says.

Richard Payne, who owns Ohio Valley Ag in Owensboro, Ky., is encouraging farmers in his area to consider planting sudangrass. Not only would farmers be able to address the nitrate issue with the crop, he contends, they would also be able to harvest it this fall.

"There is a huge shortage of hay in our area and other parts of the country. Sudangrass could be a great opportunity for farmers because it grows so fast," Payne explains.

Winter wheat is another option, say Payne and Ferrie. (See "Win with Wheat")

"If you’d plant wheat, you probably would be able to pull enough nitrogen from the ground to get you through until next spring without applying anymore, and you’d also have the cash crop," Ferrie says.

Gucker wants farmers to plant wheat or cover crops even in years when nitrates aren’t a concern. "There are up to seven months of the year when there is nothing growing on our cropland, and we lose nutrients and soil to erosion," he says. "Putting a crop out there keeps our ground protected."

Ferrie says farmers can probably forgo applying nitrogen this fall to help with cornstalk decomposition. "There is most likely enough nitrogen out there, so just chisel fields this year," he says. "If you aren’t sure about the amount of nitrates in your fields, pull soil tests to verify the levels so you can take action accordingly."


Capture Value With Cover Crops

Even if your corn or soybean crops didn’t yield to their potential this year, you still have an opportunity to plant another crop to increase your soil’s health and provide additional forage value. With moisture, many fall-planted cover crops could provide livestock feed in the spring.

Keith Johnson, Purdue Extension forage specialist, says several small grains and grasses can be planted in September or October, depending on your geographic region.

He suggests choosing some "nitrogen-scavenger" cover crops, which are crops that trap soil nitrates that would otherwise stay in your field or move into groundwater. A few good nitrogen-hungry cover crops that also provide forage benefits for livestock are annual ryegrass, winter rye and winter wheat.

"These crops can be lightly grazed in the fall if weather conditions favor growth and there is an expectation to produce more abundant forage the following spring," Johnson says.

Farm Journal Field Agronomist Ken Ferrie recommends radishes and oats for farmers who haven’t planted cover crops before.

"They’re easier to work with and they’ll freeze out over the winter, so you won’t have to worry about managing them next spring," Ferrie says.

He adds that now is the time to line up your cover crop seed supply, as there may be shortages caused by larger-than-normal demand.

Another thing to keep in mind is the type of herbicide that you applied to your corn or soybean field. Some herbicides have restrictions because residuals can damage forage crop seeding. Be sure to check your labels and confirm that the maximum restriction period has passed.

Johnson suggests checking with your local agronomists, who have had training in cover crops, for advice on herbicide and nitrogen issues. Visit the Midwest Cover Crops Council’s website at to access an online Cover Crop Decision Tool and see which cover crops are suited for your region and use.

-- Sara Schafer

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