CO2 storage in agricultural soils yields little climate gain

04-09-2023 | |
Photo: WUR
Photo: WUR

Sequestering CO2 in agricultural soils is promoted as a promising option to mitigate climate change. But is it? Several soil scientists at the Wageningen Soil Conference on 29 August have reservations. The website of Wageningen University & Research pays attention to the discussion.

In order to achieve the climate targets, we not only have to significantly reduce greenhouse gas emissions, but also sequester more CO2 in the soil. We now know from research how we can store extra carbon in soils. Stopping ploughing, planting cover after harvest, increasing the area of ​​permanent grassland, certain forms of agroforestry and restoring wetlands – all of these can lead to (more) carbon storage in the soil.

For this reason, a lively trade in carbon farming is currently emerging. Companies that want to be or become climate neutral buy certificates from farmers who store extra carbon in agricultural soils. The European Union promotes carbon farming. ‘Carbon agriculture is a necessary addition to our efforts to become climate neutral’, said European Commissioner Frans Timmermans in 2021. ‘It enables farmers, foresters and other land managers to become real guardians of our environment and climate.’

Caveats on carbon farming

Is this a suitable means to achieve the climate goals? Carsten Paul, a researcher at the Leibniz Center for Agricultural Landscape Research, thinks not. He points out that the carbon content in the soil is a dynamic balance of carbon absorption and CO2 emissions. The rule is: the higher the carbon content, the higher the respiration and emissions. Moreover, CO2 sequestration requires a tight management of decades, which can be lost again if the farmer or his successor chooses a different management. These uncertainties mean that certificates claiming the extra carbon sequestration of farmer S in place X are an unsuitable means of achieving climate goals. ‘It would be better to spend our money on emission reduction,’ says Paul.

Wageningen soil biologist Gabriel Moinet comes to the same conclusion. Sequestering CO2 in agricultural soils can contribute at most to 8% of the current climate target for CO2 reduction, but 4% is a more realistic estimate. In addition, Moinet and his colleagues are critical of the frequently heard claim that carbon sequestration in soils is a no-regret measure that contributes to food security. Their research shows that the relationship between carbon sequestration and food production depends on the specific environment. In some cases, additional carbon sequestration can even lead to damage. “We need to shift the focus from maximizing carbon sequestration to optimizing it,” says Moinet.

These conclusions are bad news for supporters of permaculture, organic and regenerative agriculture. Soil health is central to these forms of agriculture, not only to create more soil health and biodiversity, but also to contribute to the climate challenge. Regenerative agriculture is now embraced by some of the agri-food companies, but the climate benefits are limited and difficult to quantify, so that CO2 certificates and a revenue model are difficult to justify.

New app of determine amount of carbon storage

WUR, NMI and AgroCares have developed a handy measuring method and a device to quickly determine the amount of carbon storage in soil samples. This method, called SoilCASTOR, provides reliable data and saves time and money, says Van der Voort. Soon there will be an app for this approach from AgroCares.

There are major differences in the quality of CO2 certificates, says Van der Voort. There are organizations with good quality standards, but credits can also be created and sold without proper research and quality standards. The EU is looking at how to regulate carbon farming, but there are no rules yet. “It’s a bit of a wild west now.”

That does not alter the fact that carbon storage in the soil is a good idea, says Van der Voort. ‘The climate gain may be limited, but carbon sequestration is especially good for soil health, resilience to climate change and biodiversity. This is really crucial for a large part of the world’s soils.’

Ed Asscheman Online editor Future Farming