November 19, 2007
By Ralph Pearce
Size matters when it comes to tillage equipment.
David Lobb sees eroded landscapes differently than most other people. For the
University of Manitoba soil scientist, the eroded landscapes across western
Canada can be restored in a short period of time. Man and nature have caused
severe soil erosion in hilly landscapes during the past 100 years. The widespread
adoption of conservation tillage systems has slowed this degradation on many
farms but even under zero-tillage, this degradation can continue and may take
many decades for soils to regenerate. Restoring these eroded landscapes is critical
to achieving healthy productive soils.
Now if Lobb can just get those other people to listen.
The concept of landscape restoration is certainly not new. According to Lobb,
Chinese farmers have been using this as a remediation process for hundreds of
years, carrying soil in baskets from the base of hills back to the top of the
hills. The practice of restoration is based on the fact that a majority of soil
which is eroded is not degraded and is not lost from the field. It simply moves
from one area to another.
This is true because tillage erosion is the dominant form of soil erosion in
many cultivated landscapes, not wind and water erosion. In the latter cases,
where soil is disaggregated, separated and transported from the field, there
is a true degradation and loss. "The relative importance of tillage erosion
to water erosion can be very high," says Lobb, who has researched this
extensively since 1988. "Although we think of things in the west not being
intense in terms of tillage and associated soil degradation, there is tillage
erosion occurring, and that means you have opportunities to restore because
the soil that is eroded isn't washing down into a river, it tends to stay very
close, so you have that local storage of material that you can move back up."
A major culprit in the west, says Lobb, is the size of the tillage equipment.
Although producers are not tilling as deep, they are using very large equipment.
"That means you have much more aggressive levelling of the landscape,"
he adds. "They have much more of a planing effect."
Potholes and depressions a serious issue
The perception that the prairies are relatively flat, compared to other regions
of the country, can make it challenging for Lobb to win over skeptics. Some
contend that only the hilly areas of the region would benefit from landscape
restoration. But he insists there are all kinds of depressions where topsoil
settles and there may be more opportunities for landscape restoration in the
west than in the east.
In one research study, Lobb and his students found 150 to 200 depressions per
section of land, including the Manitoba Zero-Till Research Association Farm.
"We surveyed that land and found 173 depressions on that farm, on a little
less than a mile square," says Lobb. He was told that such a find was not
representative of the hilly areas across the prairies. Yet they surveyed a farm
in Saskatchewan and found 159 depressions, and a farm in Alberta with 263. "Some
tend to be very small, but they trap soil, they trap water and nutrients. They
may only be 10m x 10m, but they are little pockets where you get very deep topsoil
and around it, you have thin topsoil from past soil erosion. A lot are small
and producers tend to manage right through them, but if there are a high number
of very large ones, they manage around them."
Even in the Red River Valley, possibly the flattest part of the prairies, the
scalping of very small rises in the land by tillage erosion can be seen. The
most obvious sign of the effects of tillage erosion in the flat area is the
in-filling of surface drains. Drawing large tillage equipment across surface
drains fills them in, just like a road grader would, and they have to be cleaned
out every two or three years.
Treat the cause, not the symptom
Whether it is in the east or west, producers still seem to favour treating the
symptom, not the cause of erosion. In fact, Lobb believes much of the drive
behind precision farming and variable rate management is shortsighted. "Anyone
willing to accept those concepts should look at landscape restoration first,
and that may eliminate the need for precision farming," he says. "Precision
farming is a response to these highly degraded, variable landscapes and if you
maintain the same type of management that caused the problem, the need will
become greater and you're going to have a recurring cost. In effect, you've
dealt with the symptom but not the cause."
On the positive
Some producers are doing some form of landscape restoration without realizing
it, adds Lobb. He says there may be several producers in Manitoba who are actively
engaged in the practice. "We're just now getting into a large study to
reinforce the economic benefits of this and once that's done, I suspect more
farmers will join in," says Lobb. "A lot of farmers have the equipment,
a lot of farmers have the problem and a lot of farmers have that soil store
that can be moved, so the potential is quite high."
That approach makes sense to Dr. Gary Johnson, an associate professor of agribusiness
and agricultural economics, also at the University of Manitoba. In studying
practices like landscape restoration, Johnson maintains the simplest, best approach
to converting the skeptics is to show the economic benefits, pointing to work
done in Illinois during the 1980s as an example. At that time, the state enacted
regulations governing the amount of erosion a farmer could have taking place
on his land. "It was a serious issue, but what we found was that we didn't
have to drive people by regulation to reduce erosion levels," explains
Johnson. "All we needed to do was show them it was economically more efficient
to use reduced tillage or no-till, and the returns were there."
Recent work by Johnson using a preliminary model for landscape restoration
in western Canada has illustrated similar benefits. "If the approach works
with reduced tillage and no-till, it should work with landscape restoration,"
First thing first
On a related matter, Johnson suggests the uptake of no-till and reduced tillage
on the prairies has been a positive influence on landscape restoration, again
pointing to economic benefits as the lure. The challenge, however, is the time
stress that reduced tillage imposes on a producer. The windows of opportunity
for planting, harvesting and any form of tillage are greatly reduced, thanks
in part to variable weather conditions.
But he echoes Lobb's contention that tillage methods may have to be altered
first to make the most of landscape restoration. "If the problem is tillage
erosion, continuing to till in the normal manner just means you're going to
have to rebuild that knoll again some time later on," says Johnson.
When is flat, flat enough?
Another misconception is that flat fields are not candidates for landscape restoration.
To Dr. Tom Schumacher, there is nothing to justify such blanket statements in
agriculture today. As a professor who teaches environmental soil management
and crop-water relations at South Dakota State University in Brookings, Schumacher
stresses that each farm is different, and that even small knolls can be eroded
and therefore benefit from this for land improvement. "It doesn't take
much variation in the topography," he notes. "You don't have to have
a lot of large steep hills, just a lot of curvature in the land. This is especially
true with tillage erosion where you're levelling the field out. If you have
a lot of small hills which are sharp peaks, then tillage erosion will occur
on the hilltops."
Schumacher adds that much of the prairie region boasts some degree of topography,
despite its flat and level reputation. "A lot of that country has knolls
and the prairie pothole region has a lot of examples where this problem of erosion
on hilltops from tillage erosion makes it very amenable to restoration,"
he says. "There are knolls where you can see a fairly acute convex top
on them and that's where you're seeing a lot of tillage erosion." -30-