If you farm in the Prairie pothole region, you’re dealing with some yield loss due to tillage erosion, says Marla Riekman, land management specialist for Manitoba Agriculture.
The good news is there’s a relatively easy way to restore that lost yield potential: simply move the eroded topsoil back up the slope.
Riekman was at this year’s Manitoba Crop Diagnostic School to demonstrate the impacts of tillage implements on soil movement and highlight soil restoration techniques.
She points to research from University of Manitoba soil scientist David Lobb showing that on Prairie “hilltops,” which include any slight rise in the landscape, topsoil losses average 30 to 50 centimetres — in other words, the original topsoil.
“We slow soil losses when we move to no till, but even after 20 to 30 years that lost topsoil may not necessarily be regained,”says Riekman.
For the erosion demonstration, Riekman dug a trench horizontally halfway down a slope and filled it with corn seed before three tillage implements (a tandem disc, a field cultivator and a high-speed shallow disc unit) were passed up and down the slope.
The germinated corn seed spread four to five metres on average from the original trench under more aggressive tillage, and three to four metres on average under less aggressive tillage. But some seed was dragged up to 14 metres.
“All implements came about equal in our trial,” says Riekman. “We expected the high-speed discs would move the most soil, and they did move more corn up and down the hill compared to the tandem disc, but at seven miles per hour we didn’t get up to appropriate field speeds. We would have seen more movement if we’d got it up to 10 or 12 miles per hour.”
According to Lobb, restoring lost topsoil is the fastest way to restore eroded land to productivity.
To restore a quarter section of land takes between five and 10 days with a custom contractor working eight-hour days, said Lobb at the demonstration, and the practice pays for itself in 3-1/2 years.
When lost topsoil is moved back to hilltops in the fall, those areas respond immediately the following spring.
Riekman’s second demonstration simulated erosion by moving soil from the top and depositing it down the length of a slope. Soil was then removed from the depression at the base of the slope and put back on the eroded knoll. Eroded, control and restoration treatments were duplicated in corn and soybeans, with half of these treated with starter fertilizer and half left untreated.
On eroded plots where starter fertilizer was not used, corn plant height was around four feet. Corn plant height increased by a foot or so when fertilizer was used. But where topsoil was restored, without help from starter fertilizer, plant height reached six feet.
“We had a two-foot height difference by going from the eroded plot to the restored plot,” says Riekman.
At the bottom of the slope, where four inches of topsoil had been removed, corn plants towered over six feet and no negative impacts could be seen.
For farmers interested in attempting the practice, Lobb recommends removing a maximum of eight inches from the bottom of the slope, to avoid disrupting biologically active soil, and adding a minimum of four inches at the top of the slope.
“I think the data speaks for itself,” says Riekman. “You can get an immediate yield boost once you’ve done this work. You’re not waiting for the soil to rebuild, that’s the most impressive thing about this. As opposed to adding manure or cover crops — why not just add the soil back to where it came from?”
Riekman says several farmers approached her at the event to say they already own scrapers that could move the soil. “One farmer did a quick back-of-the-envelope calculation, and she believed she could do it for $75 an acre, including fuel but not time,” she says. “She was really impressed.”