Carbon sequestration” is a term with plenty of traction these days. Technically speaking, it refers to long-term storage of carbon dioxide or other forms of carbon to help mitigate the fallout from climate change — a subject that increasingly figures on Canada’s agendas.
In agriculture, carbon sequestration finds a home in discussions about soil management and soil health.
According to John Bennett, former director and past president of the Saskatchewan Soil Conservation Association (SSCA), Canadian farmers have had a major, positive impact on reducing Canada’s greenhouse gas (GHG) emissions in recent years through soil management practices like zero-tillage. “Farmers’ actions have likely made the largest positive contribution to Canada’s GHG inventory, but to date have not had much recognition of that contribution,” he says.
Bennett says farmers are ahead of the curve in adopting practices like zero till, and through a relentless push for input efficiencies and fuel use reductions, they have reduced emissions from production systems.
This year, the SSCA published a position paper discussing the results of the Prairie Soil Carbon Balance (PSCB) project, which measured changes in soil organic carbon in 137 Saskatchewan field sites under direct seeding management over a period of 14 years.
“The PSCB project proved conclusively that significant amounts of CO2 — averaging 0.38 ton CO2 per acre per year — is sequestered under direct-seeded cropping systems,” the authors write.
The paper argues that past carbon tax or trading schemes have failed to deliver appropriate value back to the farm gate for offsets from carbon stored in agricultural soils. “If emitters of GHGs are penalized through the imposition of a carbon tax or emission reduction limits, it is reasonable that those who are removing GHG emissions, through carbon sequestration or capture, should be compensated in equal measure,” argues the paper.
In Alberta, farmers have the option of selling carbon offsets from no till and continuous cropping of previously summerfallowed land, according to Lorraine Lynch, a spokesperson for Alberta Agriculture and Forestry. “At current carbon prices of $15 per tonne of carbon dioxide equivalent, the value to farmers is $0.54 to $0.80 per acre in the brown and dark brown soil zones and $1 to $1.60 per acre in the black and gray soil zones,” she says.
“Other opportunities for carbon credits to improve management of nitrogen fertilizers and livestock are also available.”
Henry Janzen, a research scientist at Agriculture and Agri-Food Canada’s Lethbridge Research Station, has been studying long-term changes in soil carbon for close to 30 years.
“Here at Lethbridge we have experiments dating back to 1911, from which we’ve been able to follow changes in soil carbon over time,” he says. “A lot of our work over the last number of years has been focused on the question of how management affects carbon storage in soils.”
Much of Janzen’s work is focused on studying “carbon flows” — the flow of carbon atoms from the atmosphere into plants.
“In farming, we harvest some of that material typically in grain and export it from the system often to feed ourselves, and consume it, burning it back to C02 and extracting the solar energy from it,” he explains. “Farming is about trapping C02, investing it with solar energy and using that to fuel ourselves and animals.”
But much of this biomass carbon trapped by photosynthesis goes back into the soil, in straw, residues and manure, for example, replenishing soil organic matter. Microbes then help that organic matter decay back to C02. “The amount of carbon stored in the soil is a function of two things: how much is going in and how much is being lost as C02 from the decay,” says Janzen.
He likens soil carbon to a bank balance: you either have to reduce the rate at which carbon is lost, or increase the amount going into the soil to stay in the black.
By this measure, zero till is one excellent means of maintaining soil carbon. Planting grasses and other forages on land that has been intensively cultivated may also lead to carbon gains, says Janzen.
But Janzen emphasizes that there is no set of one-size-fits-all best management practices for enhancing carbon sequestration. He says every farmer should look at the land and ask, “What works best here?”
That question should be anchored in the assumption that our decisions will impact future generations, that we leave a legacy. “We come and go but the soil stays and the soil remembers us. The practices that we impose on the land have lingering effects for better or for worse,” he says.