Soil organic carbon: the challenges of measurement and permanence
We understand better the importance of returning lost carbon to the soil. The challenge now is to measure exactly how much carbon has been returned and, more importantly, to make sure it stays there.
More and more growers are realizing that soil organic carbon (SOC) is an essential component of their fields, and an important part of the solution to climate change. Little by little, they are therefore using more farming practices that promote the presence of carbon in their soils.
To ensure that these efforts are valued at their fair price, specialists are looking at ways to 1) better measure the carbon that producers return to the soil, and 2) ensure that it stays there!
An article on our blog explains the nature of SOC and its effects on climate change and soil health. The problem is that this precious matter is rapidly escaping from fields because soils are left bare or ploughed too intensively.
Although both these practices are widespread, they have two major drawbacks: they encourage erosion, which reduces the organic matter available in the fields, and they bring a lot of oxygen into the soil. This excess oxygen binds with carbon, creating carbon dioxide (CO2), which is released into the atmosphere. CO2 is the most widespread greenhouse gas.
SOC, a precious material to be recovered
According to the best estimates, Quebec’s fields contain between 50 and 150 tonnes of carbon per hectare, and lose between 0.2% and 1% each year.
A 0.2% loss of carbon may seem negligible, but given the volumes present in the soil, it adds up to around 14,500 tonnes of CO2 equivalent for an average 250-hectare farm. That’s a considerable amount!
In short, we must do everything we can to recover this carbon and return it to the soil, while continuing to reduce GHG emissions. Why? Because SOC is a powerful tool that we absolutely cannot do without to combat climate change.
Return carbon where it belongs: in the ground!
There are two main ways of returning carbon to the ground: industrial solutions and those based on nature.
Industrial processes use various methods (often chemical) to extract carbon from the air or capture it at the factory gate. This carbon is then buried in disused underground spaces, such as old mines or old oil fields. Although many people pin their hopes on these processes, they are far (very, very far!) from being mature, and will certainly be expensive.
Nature-based solutions return carbon to the soil in a more natural way, through regenerative practices, peatland restoration or tree planting.
These natural solutions are less spectacular than a high-tech process, but… they are proven and can be implemented today. Not only do they work, but they are sustainable and remain a low-cost solution. Not to mention that, unlike the carbon stored in an old mine, they also improve soil health, which promotes food self-sufficiency.
The ABCs of carbon sequestration
Increasing soil carbon naturally also brings challenges. The first is to gradually abandon farming practices that leave fields bare and overwork the soil. In concrete terms, this means planting more vegetation for longer periods, while working the soil less. It’s quite a change!
In the field, it may mean planting a perennial meadow. Once the meadow is established, growers mow only the above-ground part, or let their animals graze it. They never touch the roots of the meadow. These roots continue to grow, year after year, without losing an ounce of carbon. In so doing, they encourage the soil’s microbial life, nourish it and facilitate the passage of water.
Other techniques also increase the SOC in a field, for example:
- Soil covered between harvests, with cover crops, winter crops, etc;
- Vegetation around the perimeter of plots (windbreaks, extended riparian strips, etc.);
- Organic fertilizers, which return to the field the plant carbon digested by livestock;
- Reduced tillage.
Requests from certification bodies
Once these new practices have been implemented, two other challenges must be met.
The first is that of additionality, i.e. measuring exactly how much carbon the regenerative practices have added to the soil or left in there! The second challenge is that of permanence, that is ensuring that this additional carbon remains in the soil.
It’s the certification bodies that want proof of additional, permanent SOC. This allows them to guarantee that companies purchasing these sequestrations can rightly claim they are carbon neutral or can sell products that are truly low-carbon.
The challenge of additionality
The challenge of additionality arises from several factors. First of all, carbon concentrations in plots changes even before the slightest action is taken, depending on soil type, topography and weather, among other factors. Before one puts any carbon back in, one often doesn’t know how much there is already!
What’s more, even though carbon is escaping from the soil at high speed, huge quantities of it remain beneath our feet. So it’s almost impossible to detect the carbon we’ve added in the space of twelve months thanks to a new regenerative practice. Before you see any difference, you need to maintain these practices for at least a few years.
Finally, building up SOC takes time. To recover all that has been lost, the new practices must be maintained permanently.
The challenge of permanence
The challenge of permanence is simple: to guarantee that a product is truly low-carbon, the SOC returned to the soil must remain there permanently, that is for at least a few generations.
Imagine, on the contrary, a windbreak hedge planted to sequester carbon and then cut down 10 years later to make firewood. The carbon that had been sequestered is then released back into the atmosphere, with zero effect on the climate.
Stimulating challenges
Far from stopping us, the challenges of regenerative agricultural practices, additionality and permanence are driving us to design tools and methods to ensure that carbon sequestration on farms is recognized at its full value. The agricultural world and society in general have everything to gain: better soils, more resilient agriculture and greater food self-sufficiency.
Do you want to get on board?
