Soil erosion concerns overblown?

Academic says soil loss to wind erosion isn’t backed up by data

The long shadow of the 1930s dust bowl may have resulted in an inaccurate assessment of wind erosion risk.

David Lobb has spent much of the last year challenging long-established beliefs about wind erosion.

The University of Manitoba soil science professor and his team recently completed a study of the historical and contemporary evidence of wind erosion on the Prairies and the findings run counter to deeply rooted assumptions about wind erosion that have persisted for nearly a century, he told the Farm Forum Event virtual conference earlier this fall.

“In the Canadian Prairies, wind erosion is ingrained in the culture of farming as it is throughout the Great Plains region of North America,” Lobb said.

“This stems out of the Dirty ’30s when the infamous dust bowl extended across the region and into Canada, devastating agriculture in the late 1930s and changing farming forever.”

Over the ensuing decades, with the assumption that wind erosion was a costly and enduring problem farmers would continue to face, various initiatives were established to combat the problem. Windbreaks were probably one of the more visible legacies that came out of the Dirty ’30s.

In the 1980s it was estimated that soil erosion was costing agriculture about $430 million per year and those losses were largely attributed to wind erosion. Those concerns fuelled the widespread adoption of conservation tillage, and the dramatic reduction of the use of summerfallow.

“The conventional wisdom is that wind erosion persists and remains a major threat to farming in the Prairies,” said Lobb. “This belief is reinforced by the dust storms we regularly see on the Prairies. Every few decades we see a big storm. We continue to experience dust storms, even small ones, with sediment blowing into ditches and creating snirt or dirty snow over the landscape during the winter.”

The snow/dirt blend known colloquially as ‘snirt’ might be unsightly, but it’s not necessarily a sign of a huge wind erosion problem, a new study says. photo: Allan Dawson

Research to assess the severity of soil erosion has been carried out since the 1990s. Predictably, the models suggest significant wind erosion in the past that has been mitigated through changes in management. They also suggest there are soils and landscapes where wind erosion is still considered to be a major problem for some cropping systems.

However, while the predicted rates of soil loss by wind erosion were substantial (20 to 30 tonnes per hectare), Lobb notes there was no regional experimental data to support these models, nor any corroborating visual evidence.

“To sort this mystery out, we selected several sites in the region considered to be moderately to severely impacted by wind erosion both historically and currently. These are sites with current predicted soil losses of 20 to 30 tonnes per hectare per year — averaged over the entire field surface, over all crops in the area, and over many years,” he said.

They expected to observe sufficient soil erosion to calibrate and validate the soil erosion models. But that never materialized. If the models were correct, there should have been evidence of topsoil deposited along the field boundaries. Lobb calculated that the banks would be two metres high and three metres wide and along every boundary every year, and 10 metres high and four metres wide over 25 years. There was only one site in the testing study area that showed any evidence of moderate to severe loss, but based on Cesium-137 data, it was dated back to before the 1960s and was likely a remnant of the 1930s climate event.

“So the conclusion has to be that there was severe wind erosion many decades ago but never since then,” said Lobb.

Knowing that their conclusion would raise eyebrows, Lobb and his team broadened their research. They did two more studies of wind-eroded sediment: a survey of ditches; and a survey of wetlands. Both studies came to the same conclusion: wind erosion is very noticeable but the soil loss resulting from wind erosion is very small.

It appears that the only conclusion that can be drawn based on all of these studies, is that wind erosion does not actually result in much soil loss or sedimentation in the Canadian Prairies and possibly in other areas in the Northern Great Plains region.

In an interview after the conference, Lobb said it hasn’t been easy to win over converts to these conclusions, especially when there’s a time limit.

“When I have presented our current scientific research on wind erosion, I normally observe great disbelief and outright rejection of our conclusions,” said Lobb. “A 20-minute presentation is necessarily thin on details and taking people through the full presentation of observations and logic typically takes about one to two hours.”

Lobb notes that people have very firm ideas about soil erosion.

“These are ingrained from the scientific community to the media, and into the government and industry. Unfortunately, soil erosion, as with most environmental systems, is a bit complicated and difficult to simplify. A simple story is always preferred, and once we have one, it is very difficult to rewrite the story,” said Lobb. “But, facts don’t lie.”

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