What goes down should go up | Sloped fields can experience tillage erosion unless soil is shifted from the bottom to the top
CALGARY — Soil movement from higher spots to lower spots in a field lowers production potential and increases variability.
What can be done about it?
University of Manitoba soil scientist David Lobb has numerous suggestions, the most drastic of which is to move soil from the bottom of slopes back to the top.
Lobb told the Precision Ag Update Feb. 27-28 about research that showed yield increases of 10 to 33 percent when soil was moved from depressions back to higher spots. In dry years, he recorded yield increases of 39 to 133 percent in Manitoba research.
On one of three sites, productivity was significantly reduced in the lower areas from which soil was taken, but there was still a net increase in crop production overall, said Lobb.
Yield response also continued for several years after the soil was moved. Given that added topsoil improved water retention and nutrient status, he said the cost of moving the soil could be recovered within four to six years.
It is potentially a one-time-only repair to degraded knolls, “so long as you don’t keep tilling the crap out of it,” Lobb said.
It is more economical than soil sampling and increasing nutrients every year. It might also eliminate the need for precision farming operations such as variable rate fertilization, he added.
“You’re never going to get rid of the variability, but the thing is, you may reduce the variability to the point where you don’t have to rely on precision farming,” Lobb said in an interview after his presentation.
“You can’t just manage the symptoms. You have to manage the cause.”
Some farmers apply manure to eroded hilltops, which can be effective but has to be done repeatedly. Putting topsoil on the same places can allow crops to produce enough biomass each year to retain the soil and improve productivity indefinitely.
Lobb said landlord-tenant agreements in England once required farmers to move the soil from the bottom of slopes back to the top.
“It’s not a new idea. It’s a very old idea.”
Even so, it hasn’t been popular in the scientific community, which Lobb contends is because most soil programs revolve around protecting against water and wind erosion. U.S. researchers in particular have been reluctant to accept his views.
“Once you start to suggest that programs that have run over the last several decades have missed the target — in other words, they’re not conserving soil to improve on farm productivity, they’re more directed at wind and water quality off site — that becomes problematic because it causes them to have to shift their program, and they’re usually very reluctant.”
He said Canadians have been more receptive, and preventing tillage erosion is part of the national soil conservation program.
However, manufacturers of tillage tools and other farm equipment have been slow off the mark.
“I’ve been a bit surprised that they haven’t jumped at this,” he said.
“There is a huge opportunity to look at how you design tillage tools, implements, etc., to make it less erosive and have better sustainability of ag land.”
If moving soil from low to higher spots isn’t considered an option, Lobb suggested low disturbance tillage using methods that move less soil. Flexible frame implements can reduce the tendency to scalp hills, and precision farming tools can help monitor tillage depth and speed to reduce tillage erosion.
He also recommended ensuring the tractor has enough power for the tillage implement so speed doesn’t have to be modified on slopes. As well, select tillage patterns that minimize variability in soil movement and use implements that can move soil up the slope.