CO2 binding in the soil - sequestration

In addition to humus formation and agroforestry systems, there are numerous other approaches to bind CO₂ in soils in the long term. Some of these methods are established, while others are still being developed or trialled and could soon play a greater role.

What does CO₂ sequestration in the soil mean?

CO₂ sequestration describes the storage of carbon in the soil. Plants absorb CO₂ from the air and convert it into biomass using photosynthesis. This carbon reaches the soil via roots and dead plant remains. There it is processed by microorganisms and soil animals and can remain stored for years.

Why is CO₂ binding in the soil so important?

The atmosphere currently contains too much CO₂. This is driving climate change. One effective method of tackling this problem is to sequester carbon in the soil. Soils worldwide store more carbon than the atmosphere and all plants combined. Every hectare of soil has the potential to actively contribute to climate protection.

Which soils store the most CO₂?

Humus-rich soils are particularly effective. Black earth, bog and forest soils store large amounts of carbon. Even well-managed arable land can increase its storage capacity through targeted measures. The decisive factors are the structure, soil life and the constant supply of organic matter.

What role does humus play in climate protection?

Humus is the key to CO₂ storage. It is created through the decomposition of organic material. Every percentage point more humus in the soil means tonnes of bound CO₂. By building up humus in a targeted manner, farmers can actively contribute to climate protection - and improve soil fertility at the same time.

Current methods for CO₂ binding in the soil

No-till and minimally invasive tillage ("no-till"/"low-till")

• Principle: The soil is not ploughed up, but the plants are sown directly into the existing vegetation cover.
• Advantage: This reduces the release of soil CO₂, improves the soil structure and promotes humus formation.
• Status: Well established, especially in regions with soils at high risk of erosion (e.g. USA, Australia).

Intercropping and green manure

• Principle: Cultivate plants such as clover, mustard or lucerne after the main harvest to cover the soil and add organic matter.
• Advantage: These plants fix nitrogen and CO₂ from the air, increase the humus content and protect the soil from erosion.
• Status: Widely used in sustainable agriculture, but established to varying degrees depending on the region.

Composting and organic fertilisation

• Principle: Organic waste (plant residues, manure, kitchen waste) is processed into compost and spread on the fields.
• Advantage: The soil receives valuable nutrients and CO₂ is bound in a stable form.
• Status: Composting is established, but is being further improved through innovative processes (e.g. the addition of biochar).

Integration of biochar (biochar)

• Principle: Plant residues are converted into stable carbon compounds at high temperatures and low oxygen levels and incorporated into the soil.
• Advantage: Biochar can bind CO₂ in the soil for decades to centuries and improves the water retention capacity and nutrient storage of the soil.
• Status: Commercially available, but still relatively cost-intensive.

Mulching and permanent ground cover

• Principle: The soil remains permanently covered with plant residues (mulch) or ground-covering plants.
• Advantage: Mulch layers prevent CO₂ losses, improve moisture retention and add organic matter.
• Status: Particularly established in organic and sustainable agriculture.

Methods in development or testing

Enhanced Weathering (accelerate weathering)

• Principle: Rock flour (e.g. basalt or olivine) is applied to fields. Through chemical processes, weathering removes CO₂ from the atmosphere and converts it into carbonates.
• Advantage: The CO₂ is permanently bound in a stable chemical form.
• Status: Promising, currently being tested in large-scale field trials worldwide.

Microbial carbon sequestration (CO₂ storage by microorganisms)

• Principle: Special soil microorganisms (e.g. mycorrhizal fungi or certain bacteria) promote the storage of carbon in the soil by forming symbiotic relationships with plant roots.
• Advantage: Microorganisms improve CO₂ storage and increase soil fertility at the same time.
• Status: In use in research and regenerative projects, but not yet widespread.

Algae and biopolymer systems

• Principle: Microalgae or biobased substances are introduced into soils to increase organic matter and carbon sequestration.
• Advantage: Algae grow quickly and can store large quantities of CO₂ in the form of organic molecules.
• Status: Experiments are underway, particularly in the area of desert management.

Synthetic permanent humus ("Terra Preta" technology)

• Principle: Modern processes are used to develop nutrient-rich humus mixtures that store carbon in the soil for a particularly long time.
• Advantage: Permanent humus can improve the humus content of depleted soils in the long term and store CO₂ at the same time.
• Status: The first pilot projects are underway, similar to the traditional "Terra Preta" of the Amazonian peoples.

Electrical floor stimulation

• Principle: Current pulses are used to promote the absorption of CO₂ through chemical reactions in the soil.
• Advantage: Experimental method to specifically control biological and chemical processes in the soil and improve carbon sequestration.
• Status: Tested in the laboratory, but still a long way from practical application.

Visionary ideas for the future

Biotechnological approaches for "artificial roots"

• Principle: Synthetically optimised plants or additives promote the formation of particularly stable root compounds in the soil, which bind carbon in the long term.
• Status: In basic research and by biotechnological companies in the concept phase.

Soil sealing deconstruction and CO₂ recultivation

• Principle: Soils that have been lost due to development or sealing are uncovered and recultivated using special methods in order to store CO₂ again.
• Status: concept stage, requires political will and investment.

Conclusion:

In addition to traditional approaches such as humus formation and agroforestry systems, there are many innovative methods for binding CO₂ in the soil. Methods such as "enhanced weathering", biochar and microbial CO₂ storage are particularly promising. Technologies such as synthetic humus formation and electrical soil stimulation could play a major role in the future, but have yet to prove their suitability in practice. A combination of different approaches, supported by research and political incentives, will be necessary to realise the full potential of agriculture as a climate saver.