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What? Cover crops plug tile lines?

Monte Bottens, ANP Tiles plugged with cover crop roots
IT HAPPENS: Tile lines plugged by cover crop roots are a rarity, most often caused by “bellies.”
Growing healthy soil: While deep-rooted cover crops can reach the tile zone, two other tile-plugging culprits are more probable. Weigh these preventives.

Based on an extremely few tile-plugging incidents involving deep-rooted cover crops on hundreds of thousands of tiled acres, risks are negligible. Yet, this issue seems to pop up every year somewhere.

Plugged tile lines aren’t a new phenomenon, and can’t be blamed exclusively on cover crops. But yes, it’s plausible that deep-rooted cover crops such as radishes and annual ryegrass grow that deep.

Properly installed tile lines are placed on a slight grade to drain well. When the water drains from the field, only air should be in those lines. Some improperly installed tile lines have low spots or “bellies” where water and sediment accumulate. That can provide a place for any root, regardless of species, to grow.

Beware of tile line ‘bellies’
That’s what researchers at Ohio State University discovered while digging up 13 places in one cover cropped field. Tiles, even partially plugged with water and sediment, allowed roots to grow.

Several professional tile contractors tell me that properly installed tile lines shouldn’t foster root growth. They contend that, with many “farmer-type” tile plows, a perfect grade is sometimes difficult to achieve. Those bellies may be due to lack of tiling experience and/or lack of precision equipment.

Farmers who install their own tile tend to install more lines due to lower costs — raising belly risks. It’s not that farmers can’t lay tile correctly, but their margin of error may be higher.

In most situations, tile lines are dry in the fall when cover crops are growing. Roots won’t grow into “air” to any extent.

Extreme cold can do it, too
The extreme cold winter of 2012-13 led to frozen tile lines in northern Iowa and Minnesota. The lines didn’t thaw in time to drain fields in a timely manner.

Many cover crops were planted there during the summer before. The fields were too wet to plant cash crops, so farmers took the Prevented Planting insurance option.

Cover crops were implicated as the culprit of plugged tile in several complaints. A thorough investigation, however, found that frozen tile lines and lines with bellies were to blame some of the time. 

Moving forward
No seed company can make iron-clad recommendations preventing a tile-plugging risk. If plugged tile is a concern, these tips may help mitigate that potential:

• Delay planting a bit so roots don’t grow as deep.

• Lower the seeding rate of the deeper-rooted cover crops like radish and annual ryegrass. Add other species to your mix.

• Based on a very minute chance of this problem, cover-crop only the tiled acres you’re willing to risk.

The coach’s closer
Poorly drained acres may benefit from tile. But many may not need tile if you implement an aggressive cover crop plan and reduced tillage or no-till. That creates an opportunity for natural drainage to be formed — something now being observed on a growing number of acres.

Groff, who farms on the Chesapeake Bay watershed, is a cover crop pioneer and innovator. Check out his website,

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