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Micronutrient application tips

A look at copper, zinc and boron and other pointers on fertility application

A farmer applies micronutrients in the fall.

Micronutrients may only be required in small doses, but that doesn’t make them less important to your crops, and fall can be a good time to address any deficiencies.

“Much like nitrogen and phosphorus, micronutrients play a critical role in crop production and yield,” says Rigas Karamanos, senior agronomist with Koch Agronomic Services.

Micronutrients make up seven of the 16 essential plant nutrients — chloride (Cl), boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn).

Western Canada’s most common deficiencies are copper, followed by zinc and boron, says Karamanos.

Copper deficiencies have been seen in crops like wheat and barley, and to a lesser degree, in canola.

“In total, there are about five million acres that are potentially deficient in copper in Western Canada,” says Karamanos.

Meanwhile, zinc deficiencies are most common in corn, field beans, lentils and flaxseed.

“These losses are exacerbated on poorly drained or badly eroded soils, especially rich in lime,” he says.

Farmers can save money by matching micronutrient deficiencies to crop needs, says Thom Weir, a senior agronomist with Farmers Edge in Yorkton, Sask. There are times when producers can either add micronutrients or plant something else, he says.

“Make sure you’ve identified your deficiencies first and then pair it with a crop. If you’ve identified you have marginal zinc levels or a zinc deficiency, but you’ve seeded it to wheat, you’re probably not going to get very much response to the zinc,” Weir says.

Best time to apply, fall or spring?

Jeff Schoenau, a soil science professor at the University of Saskatchewan, says fall timing would work well for soil applications of micronutrients like copper or zinc intended to address micro deficiencies identified in specific regions of a field like eroded knolls.

The micronutrient may be applied selectively to these identified problem areas within the field, he says, adding that pre-plant spring applications may also be employed this way. As well, micronutrient applications can be made effectively at the time of seeding, Schoenau says.

Post-emergent foliar applications of copper, zinc and boron can also work well when a need is identified, he says.

Schoenau notes that the most suitable time and method of application depends on the micronutrient element that is in short supply, and can also be influenced by soil conditions.

“For example, soils that are calcareous at the surface may readily fix and strand micronutrients like copper and zinc that are broadcasted due to reactions with the carbonates,” he says. “Under these conditions, foliar application or banding is anticipated to be more effective.”

Karamanos says oxide forms of fertilizer can also be effective in fall applications.

“Oxide forms of micronutrients have low solubility, but are converted in the soil over time to more available forms for uptake by the crop the following spring,” Karamanos says.

Fine powdered particle size accelerates the increase in solubility of oxides to the degree that spring applications could become available to crops during the same growing season, he adds.

A uniform distribution of micronutrients is key, as it benefits root interception and plant uptake.

Weir cautions that for boron, there’s potential for making the soil toxic.

“Boron is the one we think of first when talking about toxicity, and usually that’s seed-row applied,” says Weir.

Boron can be dissolved and applied as a liquid, but the problem with that is solubility.

“So, in places with lighter soils, it may leach away. And traditionally, those are the soils that you would find boron being deficient,” Weir says.

Playing a critical role in crop production and yield, many growers are now turning to micronutrients to help reach those operational goals. photo: Koch Agronomic Services

Identify causes

However, before farmers make any expensive applications, it’s important they determine if their soils are genuinely deficient in micronutrients.

Soil moisture and temperatures can provide misleading signs. Cold, wet soils may restrict plant root growth, and thereby reduce the area that soil roots explore, Karamanos says.

“Prairie soils can be cool and wet in the spring, at which time micronutrient deficiencies may show up,” he points out.

Insufficient macronutrients, like phosphorous, can also cause what seems like a micronutrient deficiency, when in fact they are restricting a plants’ roots from exploring for other nutrients.

Karamanos adds that as higher yielding cultivars are being introduced on the Prairies, micronutrient levels in the soil are decreasing, and often reach the critical levels — or slightly above them — where hidden hunger can result in reduced yields without deficiency symptoms.

Therefore, it’s not enough to use crop symptoms to diagnose micronutrient deficiencies, warns Karamanos.

“That’s why agronomists will look for ‘multiple evidence’ before recommending a micronutrient for a whole field,” he says.

Testing recommended

There are too many instances of micronutrients being applied to fields that don’t need them, says Weir.

“I would suggest getting zone sampling done, and determine which zones actually need the micronutrients,” he says, stressing micronutrients are highly variable.

Karamanos notes micronutrient levels can vary from field to field, or even within the same field, and that any recommendations must be based on yield history, scouting knowledge, and soil and tissue tests.

Manitoba Agriculture crop nutrition specialist John Heard says soil and tissue testing can determine where and when micronutrients are likely to be deficient, as well as provide data about soil characteristics such as texture, organic matter, pH, and crop sensitivity.

“It is less of a mystery than it once was,” he says.

In general, Manitoba Agriculture urges farmers to take separate soil and tissue samples from affected and unaffected areas, and submit them to a reputable lab for nutrient analysis.

Tissue sampling is usually better than soil analysis to confirm micronutrient deficiencies.

Karamanos explains soil samples are merely a “snapshot in time” of the nutrients available.

“Depending on weather conditions, there may be more microbial activity in the soil, thus more liberation of nutrients and availability to crops,” he says.

Micronutrient soil test levels also often reflect the extreme variability of these nutrients in fields.

When tests suggest a micronutrient deficiency, apply the necessary nutrients in field test strips, evaluate crop recovery and yield and compare them with untreated areas, according to Manitoba Agriculture.

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