Small Elements That Can Make or Break a Crop
By Carol Miller, Editor, American Vegetable Grower
Micronutrients are typically measured in ounces, not tons. But these small elements play an outsized role in your crop’s success. And as more growers sharpen their focus on plant nutrition and its role in plant health, these secondary elements are moving from an afterthought to a front-line tool in crop production.
That’s good news — and also a potential landmine.
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“Micronutrients are essential, but a little goes a long way,” says Kaan Kurtural, Senior Agronomy Information Technology Manager at Wilbur-Ellis. “It’s not uncommon for toxicity to show up if application rates aren’t precisely calculated.”
The challenge? Unlike macronutrients like nitrogen or potassium, micronutrients — boron, zinc, iron, copper, and others — don’t follow a one-size-fits-all script. Their availability, mobility, and effectiveness are closely tied to your soil pH, organic matter, and even your application method.
Why It Matters
Growers across the country are incorporating micronutrients into their programs. Many, like California’s Taylor Farms, have seen striking yield and quality improvements from what Agronomy Manager Kim Horton called “a few little tweaks.”
But the margin between helpful and harmful is narrow.
“Without enough boron and zinc, flowering won’t happen. And without flowering, you don’t have a crop,” Kurtural says.
Kurtural recommends a tissue test to confirm deficiencies, rather than relying on traditional soil tests.
“Soil tests are great for pH, EC, and major nutrients,” he says. “But micronutrients like boron or zinc? They're much more accurately measured in plant tissue.”
As for sap tests? Kurtural is cautious.
“Everyone’s selling a sap test right now. But we don’t know what the values mean,” he says. “We can’t write a recommendation from it.”
“Micronutrients are essential, but a little goes a long way. It’s not uncommon for toxicity to show up if application rates aren’t precisely calculated.” - Kaan Kurtural, Wilbur-Ellis
Signs of Trouble — and How to Avoid It
Micronutrient toxicity typically shows up too late to reverse. Symptoms can vary by element, but often appear as leaf bronzing, curling, or distorted shoot growth.
“The most common cause is an application error,” Kurtural says. “Not necessarily the product itself, but a miscalculation of the rate, especially with liquid formulations. These are potent products.”
Most micronutrient formulations contain only 5% to 6% of the target metal. That’s deliberate — it’s designed to reduce risk. But only if applied with precision.
“There’s no real luxury zone with micros. They’re either deficient, optimal, or in trouble,” he says.
To stay in that optimal zone, Kurtural recommends a two-part strategy: combine soil and tissue tests, and lean on experienced PCAs or CCAs to write conservative prescriptions.
Foliar vs. Soil Application
When it comes to application, foliar feeding is often the most efficient route.
“Micronutrients are needed in such small quantities — a pint to half a gallon per acre — that foliar sprays are more efficient,” he says. “They’re taken up quickly by leaves and fruit.”
Soil application is less reliable, especially in calcareous soils, where high pH can lock up essential elements like iron or copper. That said, chemigation through drip irrigation is possible, depending on the element and the soil profile.
Flooding or pivot irrigation, on the other hand, is less likely to deliver consistent uptake.
“These nutrients aren’t mobile enough in the soil to count on uniform uptake that way,” Kurtural says.
Balancing the System
A common misconception is that adding one micronutrient will solve the problem. In reality, nutrient interactions — between micros and macros alike — complicate things.
Growers sometimes worry, for instance, that excess phosphorus might limit zinc uptake. But in most vegetable systems, that’s not a major issue.
“Soil pH and organic matter are far bigger influencers,” Kurtural says.
Micronutrients don’t operate in isolation. They’re affected by broader nutrient programs and field conditions. Residual buildup is rare but possible — especially if repeated foliar sprays coincide with poor uptake from environmental conditions like frost or heat stress.
New Tools and Technologies
Wilbur-Ellis has built digital tools to help growers make site-specific recommendations. One tool, AgVerdict, maps soil and tissue results to create variable-rate micronutrient prescriptions.
“Not every part of a field needs the same dose,” Kurtural says. “We can prescribe different rates based on irrigation output, plant tissue status — even sprayer calibration.”
Kurtural also sees promise in newer technologies like encapsulated micronutrients and nanotechnology. These tools can help extend uptake windows or improve efficiency, but they’re still in the early stages of broad adoption.
“The good news is these products can be applied with existing equipment,” he says. “So, the barrier to entry is low.”
When to Act — and Why You Must
If the risk of toxicity seems daunting, consider the risk of doing nothing.
“If you don’t apply boron or zinc, you might not get fruit set,” Kurtural says. “In almonds, for example, boron is required for pollen tube development. Without it, fertilization fails and yields crash.”
In leafy greens, iron is key to photosynthesis. Copper boosts water-use efficiency. And in heat waves — which are becoming more frequent — micronutrients delivered via biostimulants can help plants stay functional.
“I’ve seen growers lose whole fields in a multi-day heatwave,” Kurtural says. “Micronutrients can help plants avoid dehydration — like curling or premature stomatal closure — when the heat hits.”
Final Takeaway
Micronutrients are powerful tools. But they require precision, not guesswork. Invest the time in testing, use expert guidance, and calibrate your applications carefully.
“These aren’t luxury inputs,” Kurtural says. “They’re essential — but only when applied correctly.”
