Boron deficiency keeping Arkansas soybean yields low?

“A farmer in Green County told me he’d seen this problem before. He thought it was nematodes or even a virus,” says Leo Espinoza, Arkansas Extension soil scientist. “But after looking at the boron deficiency symptoms, he realized that he had the same troubles in his fields.

“We don’t know if this is a growing problem, how long it’s been around, or if it just appeared a few years ago.”

Espinoza, who spoke at the annual Arkansas Soybean Research Conference in Brinkley, said after the meeting, “another farmer came to me and said he’d seen this problem in his fields since the 1970s. He farms a short distance north of Brinkley, and his neighbor also has the problem.”

Anecdotally, most of the affected locations have been north of I-40 and west of Crowley’s Ridge. Typical symptoms include leaves being greener and thicker with a tendency to “cup” downwards. The nodes are often short and the terminal will sometimes die. Some plants recover through growth of lateral branching, but by then yield potential has been impaired. Yield losses in such cases can be more than 50 percent of expected yields.

“As we walked through fields we saw healthy plants immediately beside very sick ones. It’s strange because we see this problem across an entire field sometimes. Other times, we see it in patches or long strips within a field that’s otherwise seemingly healthy.

“Are we dealing with a problem related to the chemistry of boron or is the problem one of soil management? When it comes to boron, most research has been done on toxicity levels and not deficiencies.”

What’s curious is that cereal crops – rice and wheat – have a higher requirement for boron than soybeans. Those crops’ sufficiency levels are supposedly lower than those of soybeans. With all the rice and wheat Arkansans grow, however, “we don’t have reports of boron deficiency. That doesn’t mean it isn’t there, but it certainly isn’t showing up in a way that’s obvious.”

To illustrate the problems researchers (Espinoza is working on the boron project with both Nathan Slaton, director of soil testing, and Morteza Mozaffari, Cotton Branch soil lab director) have in studying boron, Espinoza points to a large, infrared, birds-eye-view photo.

“This is a soybean field that had a severe deficiency several years ago. We set up a large test there. Fortunately for the grower – but unfortunately for the test – the field’s deficiency cleared up. This seems to happen regularly. We want to know why the deficiency was evident two years ago and not now.”

It’s easy to see deficiencies through other infrared shots. One photo shows a field that typically cuts soybeans in the low 50-bushel range. Once deficiencies hit, however, it cut in the upper 20’s.

“We’re talking about large amounts of money lost. This isn’t just taking a few pennies away,” says Espinoza.

In preparing a study, Espinoza and his colleagues were introduced to a boron deficient field. The team took tissue samples around the V-6 stage and also at the R-2 stage.

A tissue sample of less than 20 parts per million raises a red flag of deficiency. When the levels are higher than 60 parts per million, boron may be at a toxic level. The field in question had plants testing 14 parts per million.

So, the researchers put foliar material out at 1 to 6 pounds per acre in six plots. Through later tissue samples what they found was that 4 to 6 pounds of material may have raised levels into the toxicity range. Plots receiving between 1 pound and 4 pounds raised the boron tissue levels to the sufficiency range. The 1 pound test raised the tissue samples to 41 parts per million.

Espinoza cautions that this is just one year of data and no one should act on this alone.

Paraphrasing Descartes and pointing out the frustrations of working with boron, Espinoza says, “The more you study this problem, the more you realize how little you know. By studying this problem, we keep raising questions. Why does the deficiency show up in some years and not others? Is this a physical or chemical problem? Is this deficiency going to move south of I-40? Is there a relationship between the problem and cultivars or maturity groups?”

The reason I-40 might play the role of a “boron border” is that south of the interstate, more cotton has traditionally been grown. That means more concern with boron, Espinoza says.

“According to a survey coordinated by Dr. Mozaffari, the water samples showed higher levels of boron south of I-40. We don’t know if those levels are significant or not – 14 grams in 325,000 gallons. With such low numbers, it could even be lab error. However, tissue samples south of I-40 also show higher levels of boron.

“It’s very strange. You may see both sufficiency and deficiency at the same soil test levels. Hopefully, in the end, we will be able to have a predictive tool allowing us to know where, when and under which conditions we can expect deficiencies. The only way to get to that point is to better understand how to deal with this nutrient. We need to build a database and raise awareness. Dr. Mozaffari will continue conducting a survey on boron for the next several years in hopes of providing recommendations in the end.”

Farmers in areas where this problem has been identified should consider applying 1 pound of boron per acre with their normal fertilizer applications, says Espinoza.

e-mail: [email protected]

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