Proceed with caution when it comes to micronutrients, says agronomist

It’s not hard to spend thousands of dollars on micronutrients that aren’t needed or produce little benefit, 
says Ross McKenzie

Farmers need to put on their critical thinking caps when dealing with micronutrient claims — or risk spending lots of money for no or marginal results.

There is a lot of hype surrounding supplemental micronutrients right now, said Ross McKenzie, a retired agronomy research scientist. However, not all micronutrients are created equally; some of the most crucial micronutrients — such as copper, manganese, zinc and iron — are already abundantly available in most soil in the province.

“Micronutrient fertilizers are often emphasized beyond their true significance,” said McKenzie. “A farmer might get a recommendation for two or three micronutrients. It may not seem like a lot of money at first but if the total cost is $15 per acre and a farmer has 5,000 acres, suddenly that becomes very significant. And if it isn’t returning any yield benefit and you’re spending this money, that’s the biggest concern.”

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Some fields in central Alberta might be deficient in copper for growing cereals, and zinc deficiency can be an issue when growing dry beans on some irrigated fields with sandy soil in the south. But those are rare instances, said McKenzie, who worked as a provincial agronomist for 38 years, primarily in fertilizer and agronomy research.

More often, micronutrient trials done in the province — such as boron applied to canola — find little, if any, benefit, he added.

Alberta research

Before trying micronutrients, do your homework.

This starts with soil testing followed by a “skilful interpretation” of the results. If you get a recommendation for a micronutrient, consider doing some comparative on-farm replicated strip testing to determine the benefit on your farm, he said.

Crops require 16 essential elements in order to grow properly. These include macronutrients (nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur) and micronutrients (boron, chlorine, copper, iron, manganese, molybdenum, and zinc).

The term micronutrient doesn’t mean these elements are less important — just that only small amounts are required for plant growth. And rarely are they in short supply in this province.

“As a general rule we do not have widespread micronutrient problems,” said McKenzie. “We have 25 million acres in Alberta that are cropped annually. With copper, for example, we have probably a million acres that would fall under the category of being deficient periodically when wheat or barley are grown. But that’s one million acres out of 25, so it’s a relatively small percentage.

“Those tend to be on soils in central and north-central Alberta or either the black or grey in colour or the grey-black transition soil zones. These soils will almost always be sandy and often they tend to have a low soil test for copper. It’s only really the cereal crops that would show some copper deficiency, so wheat and barley would be the two crops we’d be most concerned about on those soil types.”

As for zinc deficiency, growers mostly have that in hand.

“We identified a deficiency of zinc in the late 1980s in southern Alberta but only on sandy, irrigated soils or farms that were growing dry beans under irrigation, especially in spring in cooler-weather soils. Most bean growers now put on a small amount of zinc just to make sure they don’t run into a deficiency.”

Boron overblown

One micronutrient receiving a lot of attention lately is boron as a canola supplement. However, McKenzie said there is little scientific evidence that supplemental boron makes any difference.

“We know that canola is more prone to boron deficiency, but we did a lot of work in southern Alberta over the years with a number of crops — including canola — and even with very low soil tests we could never get a response to boron. There’s been work done in Lacombe and other places and very rarely do we see responses to boron with canola.”

McKenzie attributes this push on boron to enthusiastic micronutrient salespeople.

“This summer even the Canola Council of Canada was promoting it in one of its newsletters to help reduce heat stress and promote seed set in canola,” he said. “However, that’s based on extremely limited research in Ontario.

“In Alberta, we had heat stress but those fields also had drought or moisture stress. If you don’t have water, putting on a little bit of boron isn’t going to make up for severe moisture stress.”

He is similarly skeptical about claims being made about chlorine. While he said there have been studies touting the benefits of chlorine in certain circumstances, he wonders if farmers could get equally good results by changing their cropping practices.

“There was some good work done in Alberta in the late ’80s with chlorine and its benefit for reducing root rot in barley, but in many cases a farmer would be better off just using better crop rotations rather than grow barley on barley on barley and then develop root rot,” he said.

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