Why Tillage Erosion Is Bigger Than Wind and Water Erosion
Wind and water get their most ink when it comes to the ravages of erosion. Still, the cause of much erosion sits in the sheds of many farms: tillage tools.
That’s what David Lobb, a University of Manitoba soil scientists, told those attending this week’s Conservation Tillage Conference in St. Cloud, Minnesota. Tillage erosion is what it says: the actual movement of soil by tillage.
“It is far and away the biggest cause of soil loss, more than wind and water erosion,” he says. “It is the one (erosion form) that dominates the landscape in Canada, the U.S., and every country we looked at around the world.”
It also can key wind and water erosion. “Tillage erosion exposes subsoil that is highly erodible to wind and water erosion,” he says.
Read more: Is Tillage Stealing Your Soil?
Tillage erosion has helped fuel the total economic losses of erosion. Lobb pegged soil erosion costs and the value of lost crop yield from 1971 to 2011 in Canada from $40 billion to $60 billion in an analysis he conducted. Even though tools like conservation tillage have helped to slow soil erosion losses in recent decades, economic soil erosion losses remain high. Soil erosion losses are now magnified, as Canadian farmers are now growing high value crops like soybeans compared to wheat and barley as they did in the early 1970s.
Tillage erosion has been around a long time, even before the advent of the moldboard plow.
“In developing counties, we found the worst tillage erosion occurs wherever they (farmers) use hoes,” says Lobb. “They always pull the soil downslope, not upslope. It’s gravity.”
Environment can magnify soil erosion, such as when drought and wind combined with the exposure of bare soil during the Dust Bowl days of the 1930s. Still, erosion was also rampant in the Heavy 70s (as Lobb terms the 1970s) when farmers combined intense cropping systems with intense tillage.
The effects of tillage erosion are especially apparent on hilly ground. Ever see those yellowish knobs on top of hilltops in a field? Those knobs actually are subsoils that have had the topsoil stripped off them via tillage onto lower ground.
Tillage erosion is magnified when mechanized tillage occurs. “You will have waves of soil moving in front of an implement,” he says.
Some tillage tools are worse than others. A moldboard plow is bad for erosion, but there are more tillage operations more erosive, Lobb says. “A moldboard plow goes relatively slow and doesn’t move soil very far, 2 to 3 feet,” he says. Tillage tools like tandem disks are worse because tillage erosion is linked to speed, Lobb says.
Tandem disks cause twice as much tillage erosion than a moldboard plow, due to the amount of soil they churn at higher speeds, says Lobb. High disturbance seeders – popular on the Canadian prairies – also throw lots of soil as they pass through a field, which magnify tillage erosion.
“This all leads to the fact that you need to not just think about how much residue is left on the surface (by tillage tools), which is important for (preventing) wind and water erosion,” Lobb says. “You also need to consider how much soil is being moved. This could be your number one threat to soil, not wind or water erosion. So, consider the speed of tillage operations and how to manage the speed.”
What to Do?
Conservation tillage that minimizes the throwing the soil and, thus, tillage erosion is a start. Yet, systems like no-till simply stem the loss of soil and accompanying carbon and organic matter. Restoring soil carbon also requires stops like crop rotation and cover crops.
Some farmers around the world move topsoil that’s deposited at the bottom of fields to hilltops. In some countries, land-tenant agreements have stipulated that farmers do this. In some areas like Manitoba and Ontario, farmers have moved excess topsoil from bottom areas to hilltops using tools like earth scrapers. Multiple economic evaluations of this practice show restoration costs are recovered in three to five years due to increased yields across the landscape, says Lobb.