Soil specialist says the nation’s farmland and tillage erosion remains a problem; farmer fatigue might have set in
Soil erosion continues to cost agriculture and the economy substantially and more needs to be done to protect moderately to severely eroded soils.
This was the take home message of David Lobb’s video presentation during the University of Saskatchewan’s annual Soils and Crops Workshop that was held virtually this year.
“Conservation tillage, no-till and zero-till in particular are absolutely necessary to slow and stop soil erosion and conserve the soil. This is only the first step that must be followed by practices that restore and stabilize the health and productivity of the soil,” Lobb said.
Lobb described significant soil-management challenges and he said soil erosion is the most widespread form of soil degradation in Canada, and the greatest threat to soils in the Prairies.
He said in 1985 Don Rennie estimated the annual cost of soil erosion in Canada is about half a billion dollars, which is around one billion dollars in today’s values.
“These values were alarming at the time and this alarm was a major impetus for the development and enhancement of soil-conservation technologies,” Lobb said.
“Conservation tillage practices were developed and promoted with the coincident drop in the price of Roundup. Conservation tillage was widely adopted, zero-till and no-till increased from less than 10 percent of the crop land area to over 60 percent in areas such as Saskatchewan.”
Another key element of the soil conservation movement was the reduction in the use of summer fallow decreasing from about 25 percent in Saskatchewan in the 1980s to about five percent today.
However, Lobb said there has been a steady decline in interest to soil conservation and that a sense of fatigue has set in.
“There’s a pervasive belief amongst all the stakeholders that we know all there is to know about soil conservation, and that the job is done and we need to move on. But that is not the case. We still face some major challenges with soil management,” Lobb said.
He said a new understanding of soil erosion is forcing us to rethink what effective soil management is, because tillage erosion is the predominant cause of soil distribution within fields and the major cause of soil degradation.
“Tillage erosion is a net redistribution of soil resulting from the variability in soil translocation or soil movement by tillage, causing soil loss on hilltops and accumulation at the bottom of hills,” Lobb said.
“Over the past 30 years there have been many tillage erosion experiments and assessments and all of these studies demonstrate the tillage erosion is a significant form of soil erosion. Tillage erosion results in severe soil loss on large areas of cultivated landscapes, and tillage erosion can cause more soil loss than wind and water erosion combined.”
He said it’s important to consider wind, water and tillage erosion in combination, to get a more accurate assessment of the impacts of soil erosion on soil and its productivity.
There has been a dramatic reduction of the risk of wind erosion, water erosion and tillage erosion in Canada, but water erosion risk remains high in many parts of Eastern Canada and there are hot spots for tillage erosion across Canada.
“Moderate to severe soil loss by erosion have been greatly reduced, but they’re not eliminated particularly in some parts of the country. Nationally, the area of cropland in these higher risk classes had decreased from about 37 percent in the 1970s to about 9.5 percent by 2011,” Lobb said.
However, he said it’s important to understand these soil erosion levels are average annual rates, they do not reflect the cumulative amount of soil loss on a piece of land, it’s the cumulative loss that impacts crop yields and this is best indicated by organic carbon levels of the soil.
“The loss value in crop production due to cumulative soil losses in 1971 is estimated to be about one billion dollars per year. That’s the same value Don Rennie estimated his study back in 1986. The estimated cumulative loss value for the preceding 30 to 60 years is about $20 to $30 billion,” Lobb said.
The costs of soil erosion has continued to increase in spite of widespread adoption of conservation practices, because the value of crop production increased over the past 30 to 40 years.
The value of crop production has increased from 1971 to 2011 so the greater crop yield loss on the smaller highly eroded cropped areas translates into a much greater lost value.
“The annual lost value has increased three billion dollars in 2011 with an estimated cumulative loss value of $40 to $60 billion between 1971 and 2011. The annual loss value is expected to be similar today and the cumulative value is expected to continue to grow,” Lobb said.
“These numbers are rough, but they represent the best we have. They are considered to be very conservative and they do not include any indirect costs on either off-site or on-site environmental and agricultural impacts.”
Lobb said we need to think more broadly about what tillage is, as well as what conservation tillage is.
“Some implements may leave adequate crop residue on the soil surface to protect the soil from the erosive forces of wind and water, but they may move considerable amounts of soil with a high degree of variability resulting in substantial soil loss by tillage erosion,”
“Chisel plows and tandem discs are more erosive than a moldboard plow. We have no experimental data for new soil management tools, but it is safe to assume that ones being sold as vertical tillage are highly erosive with respect to tillage erosion.”
He said soil disturbing operations following seeding must be recognized as tillage as well, because tertiary tillage operations can result in more tillage erosion than all primary and secondary tillage operations combined.
“Conservation tillage, even if greatly improved, will not be enough to repair the damage caused by soil erosion over the past several decades. Extraordinary measures must be taken to build the soil organic carbon in moderately to severely eroded land.”
He said such remediation can be achieved by including crops and rotation that return high levels of stable organic matter to the soil over crops that don’t.
Crops such as soybeans and potatoes deplete the soil of organic carbon even under conservation tillage, so it may be very difficult to achieve a net gain in organic carbon inputs within conventional crop rotations.
“Including cover crops and rotation may be an effective means of building soil organic carbon.
Importing organic carbon to these areas may be necessary to growing organic carbon in such areas,” Lobb said.
He said one the most creative solutions that have been recognized by farmers and ignored by scientists is the practice of soil landscape restoration that takes the soil built up at the base of eroded hill slopes and moves it back to the top of the slopes where soil loss is most severe.
“This practice has been used for generations in the hilly regions of China and Europe, but has never been recognized as a soil conservation or restoration practice until recently,” Lobb said.
“Preliminary studies at Manitoba, Minnesota and South Dakota on this soil management practice have shown great promise in restoring moderately to severely eroded soils.”