Survey reveals ‘amazing’ soil loss in Great Plains region

Marla Riekman watches as a clod of soil disintegrates in water. This soil is from a conventionally tilled field with annual crops. Soils from no-till fields or perennial crops hold together longer when immersed in water. | Robert Arnason photo

MINOT, N.D. — Nearly every farmer has seen the photos from the 1930s, in which a massive dust storm is about to strike a small town or a drift of soil is almost covering a house.

What North American farmers may not know is that soil in the air or in a drift contains more than just particles of dirt.

It also contains a massive amount of nutrients.

Dave Franzen, a soil scientist with North Dakota State University, has spent several years reviewing soil survey records for the state. What he found was startling and troubling: an incredible amount of nitrogen and phosphate has blown or washed away over the last 75 to 125 years because topsoil loss equals nutrient loss.

“Topsoil contains a (lot) of phosphate and we lost an additional six inches (15 centimetres) of topsoil from 20 million crop acres since 1940. I think that’s conservative,” said Franzen, who spoke at the Northern Prairies Ag Innovation Alliance (NPAIA) conference held Jan. 10-11 in Minot.

“We would have lost an additional 12.5 million tons of phosphate and 40 million tons of nitrogen. That is the equivalent of 75 years of N and P application at present rates.”

Franzen presented the topsoil loss estimates at the Minot conference to remind farmers why zero tillage is critical for sustainable crop production.

He was likely speaking to the converted because the NPAIA was formerly known as the Manitoba-North Dakota Zero Tillage Farmers Association.

Franzen didn’t look at historical soil surveys for Saskatchewan, but it’s possible that Western Canada has lost similar amounts of topsoil.

“I can’t imagine that it didn’t happen there, too,” he said. “If you look at the old soil record, and I would challenge somebody to do that, then look at what’s left there today. I think you would see a big difference.”

He did look at soil surveys for Divide County in the northwestern corner of the state, immediately south of Estevan, Sask.

According to soil records for the county:

  • Surveyors in 1900 found 40 cm of very black topsoil in the county.
  • As of 2017, the area had no black topsoil. It has light gray topsoil.
  • Franzen estimated the loss of topsoil at 30 cm.

He discovered comparable losses in other parts of North Dakota.

“I was completely shocked. I knew we lost some soil across the state, but I didn’t think it was all that much,” he said.

“When I started to look at it and realizing how much it was and how (many) nutrients were in it, it was just amazing.”

The NPAIA conference also featured a demonstration of wind erosion.

Chris Augustin, an NDSU extension agent and soil health specialist, hooked up a leaf blower and used a tray of soil to simulate how much soil can be blown off a field in a short period of time.

“When we have these open winters, we see a lot of sediment sitting in the ditches,” he said.

“With a loamy soil, an 80 acre field under conventionally tilled soybeans, the erosion would be somewhere around 25 to 30 tons per year. Five tons would be somewhere around the thickness of a dime.”

Franzen showed modern day photos of soil accumulating in a ditch next to a field. He said the amount in the ditch is a fraction of the total loss because most of it would have blown for tens or hundreds of kilometres.

“Every time you see that (soil in the ditch), multiply it by about 10.”

Franzen’s historical numbers for soil loss are estimates, but Augustin thinks the figures are low.

“I honestly think he’s being pretty conservative,” he said.

“We’ve degraded our soils. With adoption of no till, minimal till, cover crops … we’re starting to swing that pendulum.”

Growers in Manitoba’s Red River Valley and other parts of the Prairies with heavier soil often say zero tillage is impossible in their region.

Franzen has heard the same argument in North Dakota, but he doesn’t buy it.

“I don’t hammer them on the head and tell them, ‘you’re wrong, you’re wrong,’ but there are people that have been successful … even through these wet years at making it work,” he said. “It’s mostly a fear. We have examples of success.”

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