When it comes to fertilizer, many stick to the ABCs of N, P and K, perhaps with the addition of S (sulphur). But there is a growing recognition of the need for micronutrients such as boron in plant health and performance, especially for soybeans.
Boron aids cell formation, cell wall and vascular tissue formation, node number and plant height, flower development, pollen viability, pod formation and seed set. Since it’s not mobile, plants need a supply throughout the growing season, as they can’t recycle boron from old tissues as they do with nitrogen, phosphorus and potassium. Once boron becomes a limiting factor, symptoms appear in young tissue and deficiencies can reduce flowering and pod set.
Soil tests conducted by the Fertilizer Institute across North America every five years show that several nutrient levels are declining, and as growers continue to push yields, its importance is magnified for all commodities.
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It’s why Aaron Stevanus refers to boron as a “low-hanging fruit.” He believes it’s one of the micronutrients that’s often overlooked in the chase for balancing the macronutrients in fertilizer plans.
“If we’re capping out any of these micronutrients as we push for more yield, we’re going to start running into challenges, especially if we haven’t been fertilizing for it in the past,” says Stevanus, Eastern Canada technical sales manager for The Mosaic Company. “It’s a hurdle we’re going to have to get over and understand as we move forward to drive for more off of the acre, just to keep food sustainable.”
He says boron deficiency has been associated more with alfalfa, and more attention is being paid to boron in the horticulture sector, but in row crops, it’s been overlooked.
“An average crop production fertilizer plan doesn’t have a lot of boron in it. There’s definitely more knowledge of it and recommendations in crop plans than there ever was, but there’s still a big hurdle to jump over in the next five to 10 years, especially when pushing for those higher yields.”
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Not always wrong
Mervyn Erb says boron is one of the most common micronutrient shortages in tissue tests.
“Corn, soybeans and edible beans, but the most common visual deficiency I see is in alfalfa,” says Erb, a certified crop advisor who operates Agri-Solve Agricultural Consultants, north of London, Ont. “In the last five to six years, I would say it’s not uncommon to see soil tests in the 0.2, 0.3 to 0.4 ppm range. Back in the ‘old days,’ 0.6 ppm was a really low number. But it all stands to reason — we’re removing more than we’re applying.”
In midsummer, Erb was looking at soil tests from nine fields of winter wheat, all from the same progressive grower. The P levels were all over 30 ppm and K levels were 149 to 223 ppm. But boron levels were in the range of 0.3 to 0.5 ppm. In 2021, the same grower had several fields at 0.2 ppm.
Erb echoes Stevanus about growers in horticulture understanding the importance of boron. In his area, he sees it in turnips, broccoli, cabbage and cauliflower. If there are drawbacks, they’re the cost of boron and the need for more specific research on how much is needed.
“Boron is running around $9 per pound of actual B,” he says, adding that it takes a good three pounds of actual broadcast boron to be effective, without worrying too much about toxicity. “Retailers put a pretty hefty margin on boron, however. You stab a bag with the forklift and there goes $55.”
Then there are potential problems with bin space in the tower, hand-cutting the bags open and blending boron into fertilizer mixes. And boron can’t easily be studied on its own: nitrogen, sulphur and potassium have to go hand-in-hand with it.
Research is key
The good news is there is some research being conducted on boron in soybeans in Eastern Canada. Horst Bohner, soybean specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), is in the second year of trials with The Mosaic Company’s Aspire, a potash-based fertilizer with a small amount of boron. Although he says it’s too early to draw any conclusions, he does believe the attention on boron is warranted, since it’s been shown to be an important nutrient.
Aspire is a muriate of potash-based granular fertilizer (0-0-58 per cent-0.5B) offering two forms of boron with 0.25 per cent of each form — a “quick-release” sodium borate formulation and a gradual-release (later-season) calcium borate. Company literature refers to Aspire as using Nutriform technology. According to Mosaic’s Stevanus, the forms of boron are delivered at the root level, providing season-long nutrient availability throughout the plant’s life cycle. The formulation helps with distribution, which is a primary challenge with boron, especially in granular applications and considering the amount needed. He uses Aspire on his farm because he believes it’s a superior boron-delivery system with a more uniform application, avoiding the pitfall of traditional granular boron as part of a blend, which he’s seen being toxic, deficient and sufficient all within a quarter of an acre.
The only other consideration is that boron can be taken up in two forms: as boric acid (H3BO3), which is an uncharged molecule, or as a negatively charged ion. Both forms are prone to leaching, similar to nitrate nitrogen. Stevanus says plants will also take up anion forms — also negatively charged — when pH is greater than 7.
The other factor with boron is its nutrient uptake and partitioning in soybeans, with a dramatic turn at R1 or R2, where the plant will take up 70 to 80 per cent of boron. In corn, that linear uptake starts at V8, meaning it’s needed later in the season, either with newer corn hybrids or soybean varieties.
To help with application, Stevanus says one option is to mix it using a Y-Drop system: it’s a good way to deliver nitrogen and boron in one shot, all at the root level.
“We’ve been worried about toxicity, and I’ve seen growers apply 200 pounds of Aspire, which is one pound of boron, and there are no issues,” he says, cautioning against applying it in-furrow or near the seed. “It’s one of those things we have to figure out, and determine where these new levels are — and again, that comes with more research.”
– This article was originally published in the October 2022 issue of the Soybean Guide.
