Caution urged with soil analysis

Soil scientist Ross McKenzie says he is concerned about potentially flawed soil test analysis from laboratories and what that means for nutrient and fertilizer recommendations.

There are no provincial soil test labs on the Prairies anymore, leaving farmers no choice but to send samples farther away.

As a result he sees an increasing problem with poor recommendations.

McKenzie, who for 30 years led the Alberta agronomy research program and is now a consultant, cautioned those attending the Saskatchewan Institute of Agrologists annual convention.

“Flawed analysis can lead to faulty recommendations,” he said, noting he had seen some that weren’t “even close to being in the realm of reality.”

In an interview, McKenzie said there are fairly standard methods to test for nitrogen, phosphorus, potassium and sulfur in western Canadian soils and as long as a lab uses those methods all should be fine.

For example, using the Olsen method or modified Kelowna method for phosphorous is acceptable, but the Bray method is not.

“That’s because we’ve never done any soil test calibration with that method in Alberta, Saskatchewan or Manitoba, ever,” he said.

McKenzie also said labs sometimes don’t do a good job of interpreting the numbers they get and that can spell trouble for agronomists.

“As long as they’re using the recommendations developed by Saskatchewan Agriculture they’re going to do just fine,” he said. “But if they start using recommendations on those analyses from Ontario or somewhere else, then that’s where it becomes flawed.”

Some labs will conduct an analysis called base saturation that looks at ratios of various elements such as potassium, calcium and magnesium.

“That’s really flawed in my opinion and you really won’t find a reputable soil scientist in Western Canada that would recommend that,” he said. “However, it’s being more and more frequently used to recommend potassium, calcium and magnesium to farmers, which results in applications of those nutrients that are not required or not necessary.”

McKenzie also said a clash exists between the scientific knowledge surrounding variable rate fertilizer technology and the marketing and promotion of it.

Some claims are not true and at times the practice is promoted as being of more significance than it actually is.

He encouraged agrologists to seek experts at universities and governments to make sure they use proper recommendations, and to examine new technologies from all sides.

For example, he said he began working with ESN fertilizer in the late 1990s.

“There’s a lot of really good research to show when it works, but also to show when it doesn’t work. That’s what an agrologist needs to seek out.”


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