Ways to build soil carbon

Soil carbon plays a vital role in productive farming systems. 

It supports soil structure, water holding, and microbial activity, helping plants grow and improving resilience across your land.

Carbon is stored in soil through a natural process called carbon sequestration. 

This happens when plants capture carbon from the atmosphere through photosynthesis and return it to the soil through roots, residues and organic matter. 

Over time this carbon can become stable humus, improving soil condition and contributing to climate mitigation.

Where soil carbon comes from

Soil carbon builds up from a range of sources:

• Root exudates – Roots release sugars, proteins, and organic acids that feed soil microbes and support nutrient cycling.
• Plant residues – Leaves, stems and roots contribute carbon as they break down. Roots account for around 58% of plant carbon.
• Microbial biomass – Soil microbes make up to 5% of total soil organic carbon, depending on soil activity.
• Humus – Stable carbon formed from decomposed organic matter. It improves soil structure, nutrient retention, and water holding.
• Amendments – Compost and biochar add carbon-rich material directly to the soil.

Healthy soils under active plant growth can store up to 40% of the carbon captured by plants as stable humus.

Types of soil carbon

• Labile carbon – Easily broken down by microbes. It supports active soil life and fast nutrient cycling.
• Non-labile carbon – More resistant to decomposition (for example, woody material). It provides long-term carbon storage.

Carbon levels naturally fluctuate with climate, plant growth, and land management. Productive systems tend to cycle carbon quickly, while less productive systems may store more over time.

Grasslands are especially effective at storing carbon due to persistent root biomass and continuous plant growth.

How to build soil carbon

Increasing soil carbon is about growing more biomass, protecting it, and keeping it in the soil. This includes:

• Growing more leaves, stems, and roots
• Returning organic material to the soil (for example, residues, compost, manure)
• Supporting biological activity that converts carbon into stable humus

Practical strategies

Increasing carbon in grasslands

Perennial grasses produce root biomass equal to their leaf growth. Dense, healthy plants increase soil carbon through photosynthesis and root turnover.

Tips to enhance soil carbon:

• Increase plant density and diversity
• Maintain at least 5 cm of residual leaf cover
• Promote healthy root systems
• Improve water holding through soil porosity and organic matter

Soil carbon projects and carbon farming

Farmers can earn income by increasing soil carbon through approved land management changes. These projects generate carbon credits (ACCUs) when soil carbon levels rise over time.