This past spring was one of the worst on record for so-called “snirt,” or dirty snow, in ditches across the Prairies — a sign that wind is moving loose topsoil to the margins of fields.
While snirt is an indication that fields are susceptible to wind erosion, however, University of Manitoba soil science professor David Lobb says wind and water have “negligible” impacts on soil erosion in the Prairies when compared with tillage erosion. “If you look at how much soil is lost as ‘snirt’ it’s an insignificant amount. If you lost a significant amount from every field, you’d have every ditch brimming with topsoil and that just doesn’t occur.
“Tillage is the number one soil-degrading process by far,” says Lobb.
Though Lobb’s work looks at water, wind and tillage, he says it’s primarily tillage erosion that’s responsible for soil losses and the lost productivity that currently costs Canadian producers at least $3 billion annually.
Last year, Lobb completed a detailed analysis using soil erosion modelling to determine how much the loss of topsoil from the 1980s to 2011 cost producers. In the 1980s, he says, it worked out to about $1 billion a year. But that figure has tripled in recent years.
Lobb says most estimates fail to account for losses over time. When Lobb’s team accounted for cumulative losses in their soil erosion models, they found producers have lost about $40 to $60 billion cumulatively due to soil erosion since the 1980s.
“You can go to complete zero till, and then even if you have no tillage erosion, that doesn’t eliminate the history of erosion that’s occurred,” he explains.
Because areas that have been severely eroded have very little ability to grow biomass or restore the soil, soil loss causes greater and greater economic losses because crop losses are increasingly severe on eroded land. “Your ability to regain the profit on eroded hilltops doesn’t exist,” says Lobb. By “hilltops,” Lobb means any rise in the landscape, including slight ridges or knolls.
Because producers have higher yields across the board than they did in the 1980s, and field averages have increased, Lobb’s calculations also account for potential as well as actual losses. “In 1981 you may have had a 30-bushel wheat crop on that hill, but now the potential is 50 bushels. You’ve lost a whole lot more because production has changed,” he says.
By Lobb’s estimation, there are two ways to restore lost topsoil. Producers can add organic matter such as manure to eroded areas. Or they can physically move the topsoil that shifted from hilltops to low-lying areas back to the hilltops.
The latter method has shown excellent results in experiments in Minnesota and South Dakota as well as locally, says Lobb, and when his team performed a full economic analysis of the costs associated with the practice, they found Canadian producers could recover the cost in three-and-a-half to five years — “making it the most cost-effective land improvement practice we have,” he says.
Lobb hopes to do more research on this form of soil landscape restoration to assess landscape resiliency in the face of climate change.
Producers across the Prairies are increasingly using tillage to manage soil structure, explains Yvonne Lawley, a researcher at the University of Manitoba’s soil science department.
In the Red River Valley, where Lawley conducts most of her research, there is a growing awareness that erosion is still a problem and tillage is at the very least a contributing factor. But in many producers’ minds, she believes, the issue is tied to soil compaction — they’re planting and harvesting under too-wet conditions and thus creating compaction, and they’re reversing compaction with tillage.
“We need to find solutions to the problems that tillage is trying to resolve,” she says.
Much of Lawley’s research is focused on crop and soil management, and how producers can grow good crops and also build or conserve soil.
She’s working on studies looking at corn and soybean residue management. With longer-season crops like these, there’s a risk that soil management is taking a backseat to producers’ needs to extend the growing season, planting these crops early into black, dry soil so they can fully mature before the frost.
Lawley’s field study with corn residue management compared the impact of different types of tillage on stand establishment and yield. They compared discing corn residue — standard practice for many producers in the Red River Valley — to using vertical tillage equipment. Her team didn’t find any differences in impacts on the test crops.
What was novel about that study, says Lawley, is how farmers were using vertical tillage. It’s sold to producers from a conservation standpoint because it can chop residue and leave a lot on the surface. But farmers in the study were not using it that way. They were running the equipment with a high-speed disc.
Soil temperature and tillage
Because tillage is widely used to remove residue in order to warm the soil earlier (i.e. so producers can get the crop in on time), Lawley and Lobb agree more research is needed to understand the relationship of soil temperature and moisture to stand establishment.
The impact tillage has on soil temperatures varies based on the residue type, says Lawley.
“In wheat residue we see higher daytime temperatures where we do tillage,” Lawley says. “Strip tillage has the highest daytime temperatures. It creates a rounded berm that has higher surface area.”
Yet soil temperature may have less impact on yields than producers think. Lawley had a grad student working on planting soy into different temperatures of soil — six, eight, 10, 12 and 14 degrees Celsius. “In that study we found that date of planting was more important for yield than temperature. Cold soil temperature treatments were our highest yielding,” she says.
In other words, misperceptions about soil temperature and crop performance may be fuelling tillage practices. But the paradigm that insists crops do better when planted into warm, black earth isn’t necessarily wrong, says Lawley — producers do need warm soils for good stand establishment.
“What my projects are exploring is if there are other ways to achieve warm dry soil other than using tillage, for example planting into tall stubble. It’s more than substituting product A for product B — we’re looking at many factors that need to change to make that work.”
Erosion in the Prairies is a growing problem. That’s “unmistakeable” after the last few springs, says Lawley.
“We’ve had forgiving soils in the Red River Valley, but I don’t know what the tipping point is,” she says. “Even on these soils, which we would consider higher productivity soils, these practices aren’t sustainable. The issues are accumulating.”