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Stressing soybeans may actually help

The big question is: what are you trying to achieve, more bushels? Or an easier harvest?

Plant stand losses increase significantly if rolling is delayed past the second trifoliate. Yield losses will occur.

The search to improve field-crop production never ends. Just when you think science has reached its apex, a new input comes along, a new planting practice gets tested, a new combine design gets introduced.

And, of course, somewhere a grower comes up with an idea that no one has really looked at before.

In 2017, Horst Bohner and Greg Stewart explored the prospect of increasing yield by stressing soybeans two ways. Shortly after emergence, at the V1 stage of development, they either clipped off the top of the plants or they rolled the plot.

These aren’t exactly new practices. There are growers in Ontario who have been rolling soybeans for years, yet the approach has never been researched in full detail in Canada.

So Bohner and Stewart tried the stress test this past growing season.

Stewart used the Maizex Seeds exhibit at Canada’s Outdoor Farm Show for his experiment. He set up four different treatments: a control, a plot of soybeans that were rolled on June 20, another that was cut (using a weed trimmer) on July 10, and another that was burnt with UAN on July 28. Visually, Stewart says the control had more lush growth to it, to the point where it was prone to lodging compared to the other three.

When it came time to count pods and beans in the plot, Stewart concedes the results were less satisfying than he had hoped. Both the rolled and cut soybean counts were lower than the control.

“It’s a little less exciting, simply because the pod counts we did on those preliminary trials were off compared to the pod count on the control,” says Stewart, agronomy lead with Maizex Seeds. He adds that it was an interesting concept and one he wants to continue to test this coming year. “It’s always a competing interest with other factors that rise to the top in terms of agronomic practices to be put to the test. Right now, I’m not sure that trimming the beans is going to work to a grower’s advantage.”

Cutting the beans is thought to encourage added branching by clipping the unifoliate and negating the plant’s apical dominance, where the top of a plant is the primary stem. In its absence, two stems grow and branch, increasing the number of nodes.

By contrast, the theory behind rolling beans is that bending the stems early on in their development should trigger the plant’s natural capacity to overcome stress. (Remember: soybean stands can suffer upwards of 60 per cent loss yet still reach 90 per cent of yield index.)

For Bohner, the lure of this type of stress research comes from knowing growers who have made it work. And he acknowledges other work done by Michigan State University (MSU) among other groups to help drive more in-depth study on the concept.

“I had three rolling trials and Greg (Stewart) had one at the Outdoor Farm Show site,” says Bohner, the soybean specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). “From Greg’s plot, there was no statistical difference. But from the three plots I had that were replicated, it does seem that there’s a small but real benefit to rolling after emergence — at V1, maybe even V2, and a slight benefit over rolling right after seeding.”

The majority of plants rolled during the early vegetative stages (first or even second trifoliate) do not break off and will completely recover. photo: Horst Bohner, OMAFRA

Different reasons are cited for rolling soybeans, including stone management. In much of the work done in Michigan, the intent has been to improve harvestability of the crop. From Bohner’s perspective, the primary reason for experimenting with rolling is to stress the plants and drive that compensatory capability: the more pods through stress, the more soybeans.

From Bohner’s trials in 2017, it looks as though there is about a two bu./ac. advantage to rolling soybeans at the first trifoliate. If that’s repeatable year in and year out, it’d be worthwhile doing for some growers.

Even so, is it something every grower would do with every acre? Likely not, states Bohner, but the yield boost is certainly sufficient to try again in 2018, and he adds he has no problem telling a grower who’s asking about the practice to “drive on” with the practice, no matter the size of a field.

Bohner cautions, however, that rolling is a once-per-season practice. A grower can’t come back and stress the plants a second time. The potential for breakage and yield losses is too great. The other is that even at V1, breakage is a concern with more than one pass, so care must be taken not to drive over parts of a field, like headlands, more than once.

Ongoing research in the U.S.

In fact, there has been quite a bit of research on the concept. Ken Ferrie and Missy Bauer, two field agronomists from Illinois and Michigan, respectively, have studied the impacts of rolling. Bauer’s work dates back to 2014, in which her plots indicated an average of 2.4 bu./ac. yield increase across six locations. Ferrie’s work in Illinois saw a 1.5 bu./ac. advantage.

Mike Staton, a soybean educator with MSU, learned of field rolling from growers who had been using the practice in different parts of the state. Despite Bauer’s and Ferrie’s results, it wasn’t the potential for boosting yields that drew Staton to study the concept, it was the harvest-aid benefit.

“We know the fatigue and the mechanical benefits, reducing down-time and pushing stones into the ground, and we know that there’s a benefit for seed producers, because you get fewer stones in the seed, so the seed buyers are happier,” explains Staton. “We know all of those benefits as a harvest aid, but is there an economic return? Does it make you money in any way, either by reducing harvest losses or by stressing the plants?”

That, says Staton, still requires more research.

One of his co-operators wanted to learn more about the benefits, especially in terms of the harvestability of the crop as opposed to its physiological response. But among those who were rolling their fields, some were saying the window between planting and emergence was relatively short in some years, and if they couldn’t finish the job then, they wanted to know, could they come back shortly after emergence and get the same effect without damaging the soybeans?

“They’re taking a little different approach and looking at extending the field-rolling window, so that you’re not rolling when it’s too wet, and yet still get the harvest-aid benefit,” says Staton. “That’s more the question of rolling post-emergence.”

Based on his second year of research in 2017, Staton found that rolling should be conducted during the heat of the day, when the plants tend to be more wilted, and V1 is the preferred crop stage for doing it. Staton says that in eight locations in the past two years, only one site showed a statistically significant yield increase — although it was considerable — more than four bu./ac. higher. The site was near Bay City, in a high-yield environment with populations ranging from 123,000 to 127,000 plants per acre. By season’s end, the rolled beans yielded 72 versus 68 unrolled.

“There are a number of things that have been found, and one is that if you don’t want to damage the plants with the roller, rolling a field with some residue is desirable,” says Staton. “You can punch the stones in to the level you need but the roller rides over the corn residue and it just seems that there’s less soil sealing and less damage to emerging soybeans.”

Staton emphasizes that his work was to determine the impact on harvestability, not to test the physiological response. There was no statistical analysis performed on his plots. Although he did look at yield, he didn’t look at yield components (which Bauer did, studying branching, pods per plant and seeds per pod). Staton’s goals were to look at the bottom line. Does rolling cost you anything? Does it make you more money?

The harvest-aid concept was an easy illustration for the benefits of rolling, says Staton, referring to his annual Soybean Harvest Field Day, where they compared rolled and unrolled soybean strips, and their effect on harvest. In the first unrolled strip, he recalls, the combine had barely travelled 300 feet before one of the guards was broken. In front of a crowd of 60 to 80 people, it made quite an impression. Given the downtime to repair it or the level of damage a stone that size could have done had it been scooped inside the combine itself, the benefits of rolling were rather obvious.

And that’s one of the things that’s driving the idea of rolling, from Staton’s perspective. It’s the size of the heads on the combine. At 35- to 40-foot widths, the idea of watching the entire span of the head while travelling at five km/hr is unworkable; the potential for damage is too great to rely on one set of eyes.

In spite of Bauer’s — or Ferrie’s —work, and in spite of the allure of physiological benefits and yield advantages, Staton maintains that it’s the improved harvest conditions that provide the biggest financial payback. Aside from mid-day rolling and V1 to V2 staging, the only other requirement is that rolling shouldn’t be carried out unless a grower is working with a flat field. They should also avoid it if it’s a clean (tilled) field. Rolling under that condition could cause sealing or smearing of the surface, which could lead to run-off, depending on the severity of a precipitation event. Staton has seen fields that were low in residue and rolled; the sealing effect caused heavy run-off during a substantial rain event shortly after rolling.

This article was originally published in the 2018 issue of the Soybean Guide.

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Ralph Pearce

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