Corn School: Recognizing a problem with acidic soil

Soil acidity is an issue that’s gaining attention in the Northern Plains, especially in areas where no-till practices have been paired with high surface-applied nitrogen rates.

“They’re seeing this advancing a lot faster in parts of North Dakota and Montana, under traditional zero till conditions where they broadcast urea fertilizer. They find they’re acidifying the surface of the soil — just those top two inches, but it’s having major impact,” explains John Heard, soil fertility specialist with Manitoba Agriculture.

This Corn School episode features Heard and his soil management counterpart Marla Riekman discussing challenges — often un-or-misdiagnosed — with low soil pH, following Riekman’s presentation on dealing with unproductive soils at the 2023 CropConnect conference in Winnipeg.

While no-till can lead to stratification of acidic soil on the surface, low soil pH can also be a problem in tilled fields, particularly sandy soils that are conducive for growing crops such as corn and potatoes, but that don’t have high levels of calcium carbonate as a buffer, explains Riekman.

“From the fertilizer standpoint, where we’re dealing with sandy soil and high N-using crops, meaning high N fertilization on those crops, we start to see further acidification happening on those soils,” she says.

Part of the challenge in understanding the yield cost of low pH — less than 5.8 for corn — comes down to how soil tests are done.

“We often aren’t actually identifying patches of acidity in the soil very well because of the fact that we do composite sampling…pH varies a ton across fields, and we don’t see that unless we’re actually sampling specific areas,” says Riekman. Tissue testing plants in an affected area is also part of making a proper diagnosis, with manganese toxicity serving as a clue, she notes.

Liming will boost soil pH, but it’s expensive, and access to lime is limited in some of the pockets that are just starting to identify issues with acidic soils.

“One of the first impacts of acid soils is low phosphorus, so you could in the meantime, just bump up your phosphorus nutrition while while you prepare yourself to access some industrial lime byproduct,” notes Heard. “We’re surrounded by limestone in Manitoba. They mine it in Stonewall but nobody there wants to grind it into the fineness it needs to be for liming, until at least there’s a big business doing that. But at this point, we’re seeing just pockets of problems.”

Check out the Corn School episode below for more with the dynamic soil duo of John Heard and Marla Riekman on identifying and managing low pH soils:

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