Soil organic carbon – what is it and how do we measure it?

Summary

This video script delves into the concept of total carbon, distinguishing between organic and inorganic components in soil. It emphasizes the significance of soil organic carbon (SOC), which nourishes soil biology and supports nutrient cycles, crucial for plant growth. SOC also contributes to soil structure, aeration, and erosion mitigation. The script outlines methods for measuring SOC, such as the Walkley-Black wet chemistry method and loss on ignition, and discusses the relevance of SOC in carbon trading and farming systems, suggesting it as a potential revenue stream and environmental asset.

Takeaways

• 🌿 Total carbon in soil includes both organic and inorganic carbon, with inorganic carbon primarily being carbonates.
• 🔍 To isolate organic carbon, soil samples are treated with acids to remove inorganic carbonates.
• 🌱 Soil organic matter consists of decomposed plant and animal material and living organisms in the soil.
• 🧪 Measuring soil organic matter is challenging, so soil organic carbon, which is about 40% of soil organic matter, is often measured instead.
• 🌱 Soil organic carbon is crucial as it feeds soil biology, supports nutrient cycles, and contributes to soil structure.
• 💧 Organic carbon acts as a binding agent, helping to hold soil particles together, which improves aeration and mitigates erosion.
• 🌍 Soil organic carbon is significant in the context of climate change, as increasing it in soils can aid in carbon sequestration.
• 📈 For carbon farming or credit purposes, knowing the soil organic carbon levels is essential.
• 🔬 Soil organic carbon is measured using methods like the Walkley-Black wet chemistry test or loss on ignition using a LECO machine.
• 📊 The lab results provide the concentration of carbon in the soil, which can be converted into soil organic carbon stock by considering soil bulk density.
• 💰 Monitoring soil organic carbon can benefit farming systems by improving soil health and potentially generating additional income through carbon trading.

Q & A

What is meant by 'total carbon' in the context of soil?

Total carbon refers to the sum of organic carbon and inorganic carbon found in soils. Inorganic carbon is primarily composed of carbonates, while organic carbon is derived from plant and animal residues and living organisms within the soil.

Why is it necessary to remove carbonates when measuring soil organic carbon?

Carbonates are removed because they are inorganic and not representative of the organic carbon content, which is the focus when assessing soil health and fertility.

What is soil organic matter and how is it related to soil organic carbon?

Soil organic matter consists of decomposed plant and animal material, as well as living organisms in the soil. Soil organic carbon is a component of this matter, making up approximately 40% of it, and is often used as an estimate for the total soil organic matter.

Why is soil organic carbon important for soil health?

Soil organic carbon is crucial as it feeds the soil biology that drives nutrient cycles, contributes to soil structure by acting as a binding agent for mineral particles, and helps in mitigating erosion.

How does soil organic carbon relate to climate change mitigation efforts?

Soil organic carbon is significant in climate change mitigation because it represents a carbon sink where carbon can be stored, thus reducing the amount of carbon dioxide in the atmosphere.

What are the two forms of soil organic carbon mentioned in the script?

The two forms of soil organic carbon are labile carbon, which is readily available to feed soil biology and drive nutrient cycles, and recalcitrant carbon, which is more stable and persists longer in the environment.

What is the purpose of measuring soil organic carbon in farming systems?

Measuring soil organic carbon helps farmers understand and improve soil health, structure, and fertility, which can lead to better crop yields and potentially open up opportunities for carbon trading or credits.

How is soil organic carbon typically measured in a laboratory?

Soil organic carbon is commonly measured using either the Walkley-Black wet chemistry method or through loss on ignition using a machine like a LECO, where the carbon is burned off and measured.

What is the significance of bulk density in calculating soil organic carbon stock?

Bulk density is important because it allows for the conversion of soil organic carbon concentration per unit volume to an estimate of the total carbon stock in a field, which is necessary for carbon trading and assessing soil carbon sequestration potential.

How can soil organic carbon measurements benefit a farmer?

Soil organic carbon measurements can help farmers improve soil health, structure, and fertility, which can enhance crop productivity. Additionally, it can provide opportunities for carbon credits and trading, potentially generating additional income.