New research has found that prairie farmers can increase yields by moving soil from the bottom of a slope to the top of a knoll.
“Farmers have been doing this for hundreds of years because they know this is what you have to do if you have a lot of severe erosion,” said David Lobb, a soil scientist at the University of Manitoba.
“Not necessarily on the Prairies and not necessarily in Canada … but if you look at Asia, it is a standard practice and always has been.”
Read Also
Sask. ag group wants strychnine back
The Agricultural Producers Association of Saskatchewan has written to the federal government asking for emergency use of strychnine to control gophers
To determine if such a practice would work on the Prairies, Lobb and Diane Smith, a former master’s student in soil science at the U of M, conducted trials on four sites in Manitoba, moving 10 centimetres of accumulated soil from a lower slope back onto a hilltop.
They found that adding soil to the tops of knolls increased yields there by 31 to 133 percent.
Smith also tracked the yield changes on the lower slopes from where the 10 cm of soil had been removed. She found a slight decrease in yield but not enough to make it statistically significant.
Earth movers shaved 10 cm of topsoil from the lower slope of a hill on a field near Treherne, Man., one of four test sites for the project along with Bruxelles, Swan Lake and Brookdale, and moved the soil to a 12 by 15 metre plot on the hilltop.
There was barely anything on top of the knolls before the soil was added, said Smith, who is now a soil specialist with Manitoba Conservation.
“There was no topsoil …. A lot of time you’re plowing into the C Horizon (soil zone).”
In contrast, the researchers found more than 0.6 metres of topsoil at the bottom of some hills.
In 2005, barley was planted and harvested on the test plot and on an adjacent control plot with no added soil.
Smith found barley yields of 4,472 kilograms per acre on the control plot and 5,843 kg per acre on the plot with added soil, for an increase of 31 percent.
Peas were planted on the same site in the second year of the trial, and yields were 64 percent higher on the plot with the additional 10 cm of soil.
At the Bruxelles site, wheat yields were 1,967 kg per acre on the control plot and 4,586 kg per acre on the soil addition plot, for an increase of 133 percent.
Lobb’s economic analysis of the practice showed that farmers would be able to recover the cost of moving soil in their fields after four to five years, thanks to the higher crop yields.
He said he wasn’t surprised that yields increased on the tops of hills without substantial losses on the down slopes, considering that it was once a common practice in Europe.
“You can find old photos … and they have one set (of photos) from France where they show farmers filling up wagons with soil at the bottom of the slope and taking up to the top of the slope and dumping it off.”
He said there has been a misconception in North America that wind and water are the primary forces behind agricultural soil erosion, but recent research indicates otherwise.
“In the last 20 years we’ve become very well aware, as a science community, that it’s not wind and water erosion that causes our soil landscape variability; it’s tillage erosion.”
Lobb, who has conducted field trials in North America and published journal articles on tillage erosion, added that it’s not just conventional cultivators that move soil downhill.
“When we compare the no-till seeders to other implements, the high disturbance ones cause as much tillage erosion as the mouldboard plow,” he said.
“So even in what you call a zero till system, you’re going to have soil moving down slope. And this explains why many of the farmers who are into zero till have not seen dramatic improvements in crop yield on hilltops.”
As well as measuring changes in yield, Smith also wanted to know why the additional soil boosted production.
Because the amount of nutrients was sufficient in the control plots, Smith concluded that increased soil organic matter and the related gain in water holding capacity was making the difference.
“We could say that adding soil organic matter … does increase crop yield on severely eroded hilltops,” she said.
Lobb is continuing his landscape restoration studies with researchers from South Dakota State University on test sites in Minnesota and South Dakota.
