In the “Carbon Farmers” project, Lidl, Boerenbond, Boerennatuur, the Soil Service of Belgium and Rikolto support nine Belgian farmers to store more carbon in their soil. But how do you measure that? Enter: carbon accounting. Mieke Verbeeck from the Soil Service of Belgium visited the participating farmers over the past months to establish this accounting.
"With our carbon accounting, we estimate how much CO2 can be sequestered in the soil and potentially in woody biomass,” explains Mieke Verbeeck. “For the farms in the project, we will examine how the soil management of the farm translates into CO2 emissions, but also how much CO2 they are capturing in their soils.”
The accounting focuses on organic carbon and CO2, but also on nitrous oxide emissions linked to soil management. "Carbon is continuously being built up and broken down in the soil,” Verbeeck explains. “We estimate the input of carbon that takes place through crop residues from main crops, cover crops, and fertilisation," she clarifies.
"In addition, we take into account CO2 emissions associated with the breakdown of carbon and the use of nitrogen fertilisers and lime—a product that farmers use to improve the soil's acidity." Nitrous oxide, a potent greenhouse gas, receives special attention. "It is released during the breakdown of organic matter, during fertilisation, and through the use of nitrogen fertilisers," says Verbeeck. "By monitoring these sources, farmers can take targeted action."
The carbon accounting is tracked in a detailed Excel sheet. "We collect annual data on fertiliser use, crops grown, the percentage of fields with cover crops and more." This tool allows farmers to adjust the impact of their soil management. "They can better estimate what certain measures actually achieve," explains Verbeeck. “Lidl, on the other hand, can assess which measures among farmers reduce emissions in their supply chain the most. They can then support these practices among the farmers who supply them.”
1. Smart cover crops: Japanese oat mixes or winter rye contribute more carbon than, for example, yellow mustard.
2. Crop rotation for animal feed: Traditionally grown maize contributes little to carbon build-up in the soil.
3. Sowing clover grass instead of regular grass: Clover grass fixes nitrogen in the soil, reducing the need for synthetic fertilisers, thus lowering nitrous oxide emissions.
4. Converting a field into flower strips: This promotes additional carbon storage, increases biodiversity, and is supported by European agricultural policy.
5. Using solid organic fertilisers and soil improvers like compost, wood chips, and manure.
6. Experimenting with legume-based cover crops like clover grass, which fixes nitrogen in the soil, reducing the need for nitrogen fertilisers in subsequent crops, thus lowering nitrous oxide emissions.
7. Expanding hedgerows: Planting wild hedges that can be cut after 10 years and ideally processed into wood chips for use as mulch. Wood chips are a stable carbon source and store CO2 for a long time.
“For farmers, more carbon in the soil means better soil quality, making our soils more resilient to climate change,” explains Verbeeck. "By growing clover grass or legume-based cover crops, farmers need less synthetic fertiliser. This not only avoids indirect CO2 and direct nitrous oxide emissions but also saves costs. Additionally, more hedgerows, flower strips, and trees, increase biodiversity."
So many benefits... Why aren't these practices standard? “Experience shows that a farmer begins to see the first benefits of soil carbon storage after five years,” says Jana Roels, climate and sustainability consultant at Boerenbond. “Furthermore, there are extra costs in the short term such as purchasing cover crops and compost.” New risks also emerge. “Reducing fertiliser use requires experimentation. If a farmer is poorly advised or unlucky with the weather, yields can drop significantly. Converting arable land into flower strips also leads to lower yields.”
In short, the transition can only succeed if the risks are not borne solely by the farmer, and if the farmer is compensated for providing ecosystem services.
Carbon accounting is a crucial tool in this transition. However, there are still many challenges. "To estimate the amount of carbon being built up in the soil, we use the currently known estimates of carbon inputs and outputs," says Verbeeck. "Unfortunately, this data is not available for all crops—and especially not for combinations of crops. Further research is needed here."
Nevertheless, the first results to be released in 2025 will already provide many valuable lessons. With carbon accounting, the project has taken a crucial step. “Farmers now have a tool to improve the CO2 balance of their soil. And what's good for the soil is good for the planet, but also for their wallet. The better we can measure carbon storage, the better governments and companies like Lidl can reward farmers for it. This way, we make sustainable agriculture economically viable."
.png)
