Can cover crop roots clog field tile? Reports of tile clogging in Indiana rolled in this spring to Purdue University Extension agronomist and cover crop specialist Eileen Kladivko. "Rarely did I hear about it in the past," said Kladivko. "This year I heard about it a lot."
It wasn't just Indiana farmers having problems. Ohio farmers also reported unusual tile clogging this spring, said crop consultant Dan Towery, Ag Conservation Solutions.
Among those calling Kladivko was Ruth Hackman, Washington County, Indiana, NRCS District Conservationist. Two farmers in her district had reported clogged tile. Except for their relatively close proximity, the two farmers' situations had little in common. They planted different cover crop seed mixes. One planted spring oats and radishes; the other cereal rye and radishes.
The tile systems were also different. The tile line that plugged for Brian Wischmeier in Brownstown, Indiana, was a 40-year-old plastic line, 30- to 48-inches deep. "The other farmer's tile system was less than 10 years old," said Hackman. "And fairly shallow at 28 inches."
Neither farmer had ever had a tile clogging problem before this past spring, despite having planted cover crops for four years or more. But this spring, field tile clogged in six places in one of Brian Wischmeier's corn fields.
Some 70 miles north -- in Shelby County, Indiana, -- Mark Nigh and a neighbor also had clogged field tile this spring, apparently plugged with cover crop roots. It was also the first time for a clogging problem for these farmers, who have been seeding cover crops for four years or more. They had seeded cereal rye and radish.
Root samples pulled from Wischmeier's plugged lines were sent to a Purdue University lab for analysis. "The results were inconclusive," said Hackman. "However, the lab ruled out brassica roots." That means the sample roots weren't radish roots. Since spring oats and radish were the only cover crops planted in the fields, it's a fair assumption that oat roots clogged the field tile. But oats couldn't have been the culprit on the many plugged tiles where farmers seeded cereal rye.
WHY THIS YEAR?
So, why did fields that had been in cover crops for four or more years plug for the first time this last spring? Why did it happen with different cover crop seed mixes? And, why did it happen in some fields and not others -- and in some parts of fields and not in other parts? Purdue's Kladivko concedes up front that she doesn't know. "We have theories, but we're guessing on all of it."
What are the theories so far? On the question of why the problem showed up this past spring for the first time, Kladivko, Towery, Hackman and Wischmeier all agreed that the unusually favorable growing season for cover crops played a role. "This past fall's growing conditions were super for cover crops," said Kladivko. "We had a warm late fall and our winter was relatively warm. In short, we had a long window for good cover crop growth -- more than typical.
"And then in the spring the cover crops that overwinter, such as cereal rye, really took off," she added. The wet spring triggered rapid growth. It also delayed farmers, such as Mark Nigh, from getting their sprayers into the fields to terminate the cover crop -- so roots grew longer into the spring.
"One of the reasons we seeded spring oats and radishes is that they winterkill," said Wischmeier. So, we don't have the issue in the spring of getting the cover crop killed. Oats and radish help hold the winter annuals down, and radishes sequester leftover nitrogen in their tubers.
"If oat roots clogged the tile, as evidence suggests, it was probably due to their having a longer than normal growing period," said Wischmeier. The field with the clogging problem flooded out in early August, killing the soybean crop -- the first loss of a growing crop in the field in 40 years. "After the water receded weeds started coming on," said Wischmeier. "We thought we'd seed the cover crop early -- in late August -- to get more growth and organic matter. Looking back," said Wischmeier, "that was probably not a good idea."
Normally, oats and radishes would have frozen out by December. Last winter, however, the crop didn't kill out until January. "By that time it was waist high," said Wischmeier.
He planted the field to corn on April 20 and didn't notice any drainage problems. "Within the next week, however, we got a couple of inches of rain," says Wischmeier. "I didn't think the field looked quite right. Then we received another inch or two of rain and I knew there was something very wrong. We had water standing above where the tile main ran and we thought the main had collapsed. So, we brought in an excavator and started digging."
They found five laterals across the field plugged tight with roots near where each joined the main line. In all cases the tile was plugged only 2 to 3 feet from the main. "It was a real mess," recalled Wischmeier. But aside from the plugged sections, the tile line looked clean with no sediment and no water pooling.
Wischmeier believes the main problem was that the cover crop grew too long and too well. "We grew corn in an adjoining field, and planted the same cover crop mix in that field after harvest in early September. The cover crop in the later-planted field didn't get as well-established and we had no tile clogging problems in it."
Yet, how and why did the oat roots get down so deep? "It still floors me that there could have been oat roots in the tile," said Wischmeier. "I thought oats had more of a fibrous root and were not deep rooting." It was a dry fall and the clay soil cracked. He wondered if the roots followed cracks down. Or, because the field had been no-tilled maybe the roots followed night crawler holes that seemed prevalent over the tile main.
Why did the clogged tile line problems show up so late in the spring? One of the Shelby County farmers speculates that grass roots entered but did not plug the tile lines when the plants were alive. Then after the plants died, their dead roots started sloughing off in the tile and were carried along the line. As they were carried along they accumulated with other dead roots until the mass grew large enough to plug the tile, which can happen more easily at a junction of laterals with the main.
Towery cautioned farmers against jumping to conclusions. He pointed out that percentage wise, very few cover crop fields had tile clogging problems. And, he added, some clogging could have been caused by corn roots. That, of course, doesn't explain the clogging on Wischmeier's field where the previous crop was soybeans or the fact that corn has been raised on most of these fields for years without clogging problems. Towery also speculated that some clogging may have been aided by improperly laid tile with snags that catch roots, or with dips in the line to attract roots.
If a tile line is the same from year-to-year, why would it clog this year and not in previous years? "It may be that in most years the roots don't get down to the tile to show the problem," said Kladivko. "A tile system is unlikely to be perfect throughout a field," she explained. "If you've got a little bit of a dip in a line where water is always sitting it won't likely affect the functioning of the tile system. However, it could attract roots into the tile line where they can proliferate." She added that residue or sediment in the line can also cause water to pool and attract roots.
Kladivko also warned that internal couplers, where tile line laterals are connected to the main line and stick out into the main a small distance, may provide places to snag and accumulate dead roots in log-jam style until enough accumulates to block the tile.
WHAT TO DO?
With no hard answers, what should farmers do this fall?
-- Manage cover crop growth. "While I think last year was an unusual circumstance, we'll never seed the cover crop that early (late August)," said Brian Wischmeier. "If we get another odd year when there's extremely large cover crop growth, we'll terminate it early," he added. "Letting cover crops grow tall adds a lot of organic matter," noted Kladivko," but if it's a tile field, you maybe don't want to let it grow that tall." If you're concerned about wet soils keeping you from terminating the cover crop, Kladivko said using an ATV sprayer could be a good option.
-- Change seed mix. "Alternating winterkill cover crops with those that overwinter is an option to lessen risk of tile clogging," said Kladivko. She noted, however that with a winterkill mix you lose the benefit of having a cover crop growing in the spring. Brian Wischmeier said he's considering planting wheat in the mix instead of oats, but hasn't made up his mind.
-- Keep residue from entering tile lines. "Residue can slip through holes in risers and into tile lines restricting water flow and causing pooling," said Kladivko. She recommended screening risers -- especially if you're using vertical tillage. Installing blind inlets is another option.
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