Building Soil Organic Matter: Practices, Timelines, and Returns

Soil organic matter (SOM) is the foundation of healthy, productive farmland. It's the carbon-rich material derived from decomposed plant and animal residues, and it plays a critical role in water retention, nutrient cycling, soil structure, and carbon storage. For farms facing climate volatility, rising input costs, and sustainability reporting requirements under CSRD, building soil organic matter is no longer optional—it's a competitive necessity.

Yet many farmers face a common challenge: soil organic matter doesn't build overnight. It requires consistent management practices, patience, and a clear understanding of which interventions deliver the best returns. This article explores the most effective practices for increasing SOM, the timelines involved, and the economic benefits that make the investment worthwhile.

What Soil Organic Matter Does

Soil organic matter is far more than just “dead stuff” in the ground. It's a dynamic component of soil health that delivers multiple benefits:

• Water retention: SOM acts like a sponge, holding up to 20 times its weight in water. In drought conditions, this can be the difference between crop failure and a viable harvest.
• Nutrient cycling: Organic matter slowly releases nitrogen, phosphorus, and other essential nutrients, reducing the need for synthetic fertilizers.
• Soil structure: SOM binds soil particles together, improving aggregation, reducing erosion, and enhancing root penetration.
• Carbon storage: Every percentage point of SOM represents roughly 10 tonnes of carbon per hectare stored in the soil—critical for carbon credit schemes and climate mitigation.
• Biological activity: SOM feeds soil microbes, fungi, and earthworms, which in turn improve nutrient availability and disease suppression.

In short, soil organic matter is the engine of soil fertility. Without it, even the most intensive chemical inputs will fail to deliver sustainable yields.

Current Benchmarks: Where Does Your Soil Stand?

Across the UK and EU, soil organic matter levels vary widely depending on land use, climate, and management history. Typical ranges include:

• Arable soils: 2–4% SOM (lower in intensive cereal systems, higher in rotations with grass leys)
• Permanent pasture: 4–8% SOM (higher in wetter climates, lower in overgrazed or degraded pastures)
• Peat soils: 20–60% SOM (but often in decline due to drainage and oxidation)

Many intensively farmed arable soils in the UK have lost 30–50% of their original organic matter since the mid-20th century, driven by deep tillage, monocultures, and the removal of crop residues. Reversing this decline is a multi-year project, but the economic and environmental returns justify the effort.

Practices to Build Soil Organic Matter

Building SOM requires a shift from extractive to regenerative farming practices. The most effective interventions include:

1. Cover Crops

Cover crops—such as rye, vetch, oats, or radish—are planted between cash crops to protect and enrich the soil. They add organic matter through root exudates and above-ground biomass, prevent erosion, suppress weeds, and improve soil structure.

A well-managed cover crop can add 1–3 tonnes of dry matter per hectare annually, contributing 0.1–0.2% SOM over time. Winter cover crops are particularly effective in the UK, where bare soil over winter leads to nutrient leaching and erosion.

2. Compost and Organic Amendments

Applying compost, manure, or biosolids directly adds organic matter to the soil. A typical application of 20 tonnes of compost per hectare can increase SOM by 0.1–0.15% in the first year, with lasting benefits as the material continues to decompose.

Compost also introduces beneficial microbes, improves cation exchange capacity, and buffers pH fluctuations. The challenge is sourcing high-quality compost at scale and managing transport costs.

3. Reduced or No-Till Farming

Tillage accelerates the decomposition of soil organic matter by exposing it to oxygen and disrupting soil structure. Reducing tillage—or eliminating it entirely—slows this loss and allows organic matter to accumulate.

In UK trials, no-till systems have shown SOM increases of 0.1–0.3% per year compared to conventional ploughing. The benefits compound over time: less erosion, better water infiltration, and lower fuel costs.

4. Residue Retention

Leaving crop residues—straw, stalks, chaff—on the field after harvest feeds the soil rather than exporting carbon. Residue retention is particularly important in cereal systems, where straw removal for bedding or biofuel has historically depleted SOM.

Retaining 50% of crop residues can add 0.5–1 tonne of carbon per hectare annually, depending on crop type and yield. The key is balancing residue retention with disease management and planting logistics.

5. Crop Rotation and Diversity

Diverse rotations—including legumes, deep-rooted crops, and grass leys—build SOM more effectively than monocultures. Legumes fix nitrogen and add biomass, while deep-rooted crops like chicory or lucerne deposit carbon at depth.

A four-year rotation including wheat, oilseed rape, beans, and a grass ley can build 0.2–0.4% SOM over the cycle, compared to continuous wheat.

Timelines: How Fast Can You Build Soil Organic Matter?

Building soil organic matter is a slow process. Unlike synthetic fertilizers, which deliver immediate nutrient boosts, SOM accumulates gradually. Realistic expectations include:

• Year 1–2: Minimal measurable change in SOM, but improvements in soil structure, water infiltration, and biological activity become evident.
• Year 3–5: SOM increases of 0.1–0.3% per year, depending on practices. Farmers report reduced fertilizer needs and improved drought resilience.
• Year 5–10: Cumulative SOM gains of 0.5–1.5%, with significant economic returns from reduced inputs, higher yields, and eligibility for carbon credit schemes.

The rate of SOM accumulation depends on climate, soil type, and management intensity. Sandy soils build organic matter more slowly than clay loams, while wetter climates favor faster decomposition and require more aggressive carbon inputs.

Patience is essential. Farmers who expect rapid results often abandon regenerative practices before the benefits materialize. The key is to track progress annually using soil testing and celebrate incremental gains.

Economic Returns: The Payoff of Building Soil Organic Matter

The financial case for building SOM is compelling, even before considering carbon markets or sustainability premiums. Key economic benefits include:

1. Reduced Fertilizer Costs

Every percentage point of SOM releases an estimated 20–40 kg of nitrogen per hectare annually, reducing synthetic nitrogen requirements. At current UK fertilizer prices (£400–500 per tonne of urea), this represents £30–60 per hectare in savings.

Phosphorus and potassium are also mineralized from organic matter, further reducing input costs. Farms with 4% SOM typically apply 20–30% less fertilizer than farms with 2% SOM, with no yield penalty.

2. Improved Water Holding Capacity

Soil with 4% organic matter can hold 40–60 mm more plant-available water than soil with 2% SOM. In a dry spring or summer, this extra water can prevent crop stress and protect yields.

For a 100-hectare farm, this translates to an additional 400,000–600,000 liters of stored water—effectively free irrigation. In drought-prone regions, this is worth thousands of pounds in avoided yield loss.

3. Yield Stability and Resilience

High-SOM soils buffer against climate extremes, delivering more consistent yields in both wet and dry years. Long-term UK trials show that farms with SOM above 3.5% have 10–15% lower yield variability than farms with SOM below 2.5%.

This stability reduces financial risk and makes it easier to secure favorable crop insurance rates and bank financing.

4. Carbon Credits and Payments

Building soil organic matter generates carbon credits, which can be sold in voluntary or compliance markets. Under UK and EU carbon farming schemes, farmers can earn £20–50 per tonne of CO₂ sequestered.

A 0.3% annual increase in SOM on 100 hectares sequesters roughly 90 tonnes of CO₂, worth £1,800–4,500 per year. As carbon pricing tightens under the EU ETS and UK carbon border adjustments, these payments will likely increase.

5. CSRD Compliance and Market Access

For farms supplying food manufacturers or retailers with CSRD reporting obligations, demonstrating SOM improvement is a competitive advantage. Buyers increasingly demand evidence of regenerative practices, and farms with rising SOM levels can command premium contracts.

This is particularly relevant for organic, regenerative, or carbon-neutral brands, which rely on supply chains that deliver measurable environmental benefits.

Measuring Progress: How to Track Soil Organic Matter

To capture the economic and environmental returns of SOM-building practices, farms must measure progress systematically:

• Baseline testing: Test soil organic matter levels (via loss-on-ignition or dry combustion) at the start of any regenerative program. Sample at 0–15 cm and 15–30 cm depths to capture surface and subsurface changes.
• Annual monitoring: Re-test every 1–2 years using consistent sampling protocols. Compare results to baseline and track trends over time.
• Soil health indicators: Complement SOM testing with measures of aggregate stability, infiltration rate, and biological activity (e.g., earthworm counts, soil respiration).
• Record-keeping: Document management practices (cover crop species, compost applications, tillage events) to correlate interventions with SOM gains. This data is essential for carbon credit verification and CSRD reporting.

Many UK farm advisors now offer soil health assessments that integrate SOM testing with agronomic recommendations, making it easier for farmers to track progress and adjust practices.

Connecting to Carbon Markets and CSRD Reporting

Building soil organic matter is not only good agronomy—it's a climate solution with growing regulatory and market recognition. Under the EU's Corporate Sustainability Reporting Directive (CSRD), companies must disclose their Scope 3 emissions, including those from agricultural supply chains.

Farms that can demonstrate rising SOM levels and carbon sequestration will be preferred suppliers for CSRD-compliant buyers. This requires:

• Verified carbon accounting: Use third-party standards (e.g., Verra, Gold Standard, or Woodland Carbon Code) to quantify and certify carbon sequestration.
• Traceability: Link SOM data to specific fields and crop lots, enabling buyers to attribute emissions reductions to sourced products.
• Continuous improvement: Show year-on-year progress in SOM levels, not just a one-time baseline. CSRD reporting favors suppliers with measurable trajectories.

For farms enrolled in agri-environment schemes (e.g., SFI, Countryside Stewardship), SOM data can also unlock higher payment tiers and eligibility for result-based incentives.

Overcoming Barriers: Challenges and Solutions

Despite the clear benefits, many farmers face barriers to building SOM:

• Upfront costs: Cover crop seed, compost, and no-till equipment require capital investment. Solution: Access grants (e.g., Farming Innovation Fund) or carbon finance to offset costs.
• Knowledge gaps: Many farmers lack experience with regenerative practices. Solution: Join farm clusters, attend workshops, or hire a regenerative agriculture advisor.
• Short-term yield dips: Transitioning to no-till or diverse rotations can temporarily reduce yields. Solution: Phase in practices gradually and focus on long-term resilience rather than annual maximums.
• Measurement complexity: Soil testing and carbon accounting can be intimidating. Solution: Use digital tools (e.g., CarbonCloud, Cool Farm Tool) to streamline data collection and reporting.

The farms that succeed are those that view SOM-building as a multi-year investment, not a quick fix. With the right practices, patience, and measurement systems, the economic and environmental returns are undeniable.

Conclusion: The Long Game of Soil Health

Building soil organic matter is the long game of regenerative agriculture. It requires consistent management, realistic timelines, and a willingness to prioritize soil health over short-term yield maximization. But the payoff—reduced input costs, improved water resilience, yield stability, carbon credits, and CSRD compliance—makes it one of the highest-return investments a farm can make.

For SME farms navigating climate volatility and sustainability reporting, SOM is not just a soil metric—it's a competitive advantage. The farms that build it today will be the ones thriving tomorrow.