A tough nut to crack: Researchers study boron deficiency in soybeans

At midday, a welcome breeze pushes softly through golden rice and around large flocks of leggy white egrets making the grain home. We are in central Arkansas' Poinsett County, rumbling down an endless, unpaved road. The truck wheels crunch gravel and generate an enormous, gritty cloud.

“I hope there isn't anyone out walking,” says Chris Tingle, squinting at the ribbon of red dirt ahead. “I'd hate to be walking down this road and have somebody drive by. We're almost there. I promise.”

True to his word, the Extension soybean specialist soon pulls the truck into a soybean field that, at first glance, looks like a tee box for giants. Hollowed out depressions throughout the Group 5s make it appear Goliath, working on his short game, has forgotten to replace the divots.

But that isn't the case. In fact, the soybean field is deficient in boron.

I.D. the problem

One of the key's to dealing with soybean boron deficiencies is correctly identifying the problem in the first place. Farmers and consultants have seen it, but most often misdiagnosed the malady.

For that reason, says Tingle, “we need to get the word out on what the symptoms are and what we're studying. By doing so, hopefully we can help avoid future yield losses.”

But boron is proving a tough nut to crack. The problems are proving extremely difficult to duplicate in a greenhouse or lab.

“We've had to rely on field situations like this to work on. So far, we've documented boron deficient fields in Craighead, Cross, Lawrence, and Poinsett counties. We thought that the problem was only in the northeastern part of the state, but this year we found deficiencies in St. Francis County (in the eastern Arkansas Delta). We hope to run a test there next year.”

One of many strange things with boron deficiency is it can show up one year and not the next. Researchers identified a problem field last year in Cross County, put in a test this spring and deficiencies didn't appear.

“Studying this is hit or miss.”

Mainly the problem shows up north of I-40 (which basically divides the state into northern and southern halves) and west of Crowley's Ridge. What's the magic about I-40?

“We don't know, but, for whatever reason, it seems that a lot of different agriculture problems are hemmed in by I-40.”

Regardless, boron deficiency isn't a major problem. If Tingle had to guess, he says perhaps 10,000 Arkansas acres are affected. Out of almost 3 million acres of soybeans, that isn't much.

But, Tingle points out, “it's a major problem to whatever farmer is facing it. We're working with producers and county agents to find these deficient fields. That helps us get on board and do research like we're looking at today.”

The plot work currently being done by University of Arkansas researcher Nathan Slaton on this field, “certainly made believers out of these growers. They wanted us to do something. When they saw the symptoms and recognized what could happen if we didn't treat, they wanted to work with us in a big way.

“We're currently working on recommendations with boron. When should it be applied? How much should be applied? Slaton's work — along with Extension soil specialist Leo Espinoza's elsewhere — is looking at different timings and rates. The affected areas in this field are terribly obvious.”

Symptoms of boron deficiency can easily be misidentified as herbicide drift or carryover. Internode elongation of affected soybean plants is shortened.

“In ‘herbicide talk’ it's what we refer to as ‘stacked nodes.’ That means the plant, which has a full compliment of 15 to 20 nodes, is compacted.”

Tingle's hand sweeps across the field.

“Look. Some of the plants are really tall, some really short. They're all of the same growth stage, were planted at the same time, and are the same variety. If we counted the number of nodes on a tall plant versus a short plant, they'll be the same. But the difference between the lengths of nodes — which is where we set branches and pods — are vastly different.”

Symptoms can also include off-color leaves — maybe a deep maroon or purple. Terminals of the plants will sometimes die. Prior to dying, the terminals will often bend over into a shepherd's hook.

“We feel like more growers and consultants have seen this and called it something else. As far as we know, this is a new problem. However, in educating growers and agents, we're picking up more of this problem than we had just a year or two ago.”

Through study, researchers have found several things about boron deficiency. Among them:

  • It mainly shows up in a rice rotation.

  • If you do any sort of deep tillage, the symptoms aren't as likely to show up.

“By tilling, is the problem being diluted? By tilling are we allowing the plants' roots to go deeper to extract more boron? At this point, we don't know — hopefully research will tell us.”

Here's the deal: if you're in a rice rotation, there isn't a lot of tillage. Hard pan and compaction problems are common for soybean crops in such a rotation, says Tingle. The soils in this area are silt loams and can turn to “concrete” as soon as the weather gets right.

“So this could have a tillage component. We've gotten away from the plows we used 30 years ago.”

It's hard to know how widespread the boron trouble is. And it's frustrating because, “we can't tell a grower if they'll have a problem in the future. True, soil tests can tell you if soil is boron deficient, but we're not sure even that's a good indicator (of future trouble).

“If my neighbor has a field that has a problem, I may need to go ahead and apply some boron to my acreage. It's relatively cheap — about a pound per acre runs $2 to $3.”

So the problem can be fixed. But it can't be fixed during a cropping season. Once a crop is up and the problem manifests, it's usually too late to implement any control measures.

Boron is used in a multitude of physiological aspects of a soybean plant and — just as a field can be deficient — can reach toxic levels. That's a concern, admits Tingle.

“Much of the research on this has been in the Midwest, where farmers can run into toxicity. We don't want to come out recommending that everyone needs to put out, say, 5 pounds to 10 pounds of boron. That can lead to toxicity. Many people have the attitude: well, if one pound's good, 10 pounds will be better. We've got be really careful to stay away from that because toxicity is just as bad as deficiencies.”

Yield reduction associated with the problem isn't yet a given.

“After we harvest these plots, we'll have a better handle on that. I do know that harvesting shorter plants is a problem. Machinery can't get at some of the pods close to the ground. I think it's safe to say that yield loss due to this problem will be significant. But we'll see.”

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