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Carbon in your soil

Carbon levels vary across the Prairies. The ideal amount 
depends on yield expectations and the local climate

photo: lisa guenther

Great civilizations, including the Mayans and Mesopotamians, have been built on productive agricultural systems, underpinned by fertile soil. And as soil quality eroded, so did these civilizations. But when it comes to soil organic matter, it seems Western Canadian farmers have learned from the past.

People have known for centuries that dark soil is generally more productive soil, says Dr. Henry Janzen, research scientist with Agriculture and Agri-Food Canada in Lethbridge.

“And the darkness of the soil is really an indicator of the amount of organic matter. And we measure organic matter by analyzing for carbon,” explains Janzen. One of Janzen’s specialties is carbon cycling and sequestration.

Agriculture and Agri-Food Canada has long-term experiments at Lethbridge and other research stations, with the longest being over 100 years old, Janzen says. And that long-term approach is critical when it comes to measuring soil carbon changes, he says, because changes are slow and slight, above a high and often variable background.

“And sometimes it takes years or decades to see the final benefit of some of these practices,” he adds.

Building carbon

Soil carbon varies widely across the Prairies, depending partly on climate and soil factors. But management practices can influence carbon over time.

Although bumping carbon would benefit many soils, there’s no definitive level that indicates soil is too short on carbon for grain production, Janzen says. And how much carbon is ideal depends partly on yield expectations and local climate.

“So for example, if you are in the Melfort area — where you have generally higher rainfall and higher yield demands — the higher organic matter there, the higher carbon there is probably of value to you,” says Janzen. “Whereas in the Swift Current area… you probably maximize yield without needing as much organic matter.”

Historically, plant residue forms soil carbon, Janzen says. “So if you increase the amount of residue going in, you’re likely to increase the amount of carbon stored.”

Planting more perennial forages, which have large rooting systems and longer growing seasons, can help, says Janzen. Cutting summer fallow and reduced tillage can also increase soil organic matter, he adds.

Bumping yields can also bump carbon. Applying nutrients, either as fertilizer or in organic form, will reap higher yields and more residue. “If you add those residues back into the soil, that tends to increase soil organic carbon,” Janzen says.

Janzen is reluctant to offer a definitive estimate on how much carbon is being stored in Prairies soils. He says there may be local areas in Western Canada where carbon has fallen well short of optimal amounts because of erosion or improper management. But he thinks many Prairie soils are probably holding their own, or even increasing slightly.

“I think most farmers have this innate, instinctive sense that maintaining organic matter in soils is a good thing. And many, if not most, are doing things that, in fact, will preserve soil organic matter in soils” for their own benefit and that of those who farm the land after them, says Janzen.

About the author

Field Editor

Lisa Guenther

Lisa Guenther is field editor for Grainews based at Livelong, Sask. You can follow her on Twitter @LtoG.



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