Soil organic carbon – what is it and how do we measure it?
Summary
TLDRThis 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.
Outlines
🌱 Understanding Total Carbon in Soils
This paragraph introduces the concept of total carbon in soils, which includes both organic and inorganic carbon. It explains that inorganic carbon, primarily carbonates, is often removed using acids to focus on the organic carbon, which is crucial for soil health. Organic carbon is derived from plant and animal matter and is a key component of soil organic matter. The paragraph emphasizes the importance of soil organic carbon in feeding soil biology, driving nutrient cycles, improving soil structure, and aiding in climate change mitigation. It also touches on the existence of soil organic carbon in labile and recalcitrant forms, with the latter being more stable and persistent in the environment.
Mindmap
Keywords
💡Total Carbon
💡Soil Organic Matter (SOM)
💡Soil Organic Carbon (SOC)
💡Labile Carbon
💡Recalcitrant Carbon
💡Soil Structure
💡Carbon Sequestration
💡Walkley-Black Method
💡Loss on Ignition (LOI)
💡Bulk Density
💡Carbon Credits
Highlights
Total carbon includes both organic and inorganic carbon found in soils.
Inorganic carbon primarily consists of carbonates.
Organic carbon is derived from plant and animal residues and current soil life.
Soil organic matter is challenging to measure directly.
Soil organic carbon is used as an estimate for soil organic matter, representing about 40% of it.
Soil organic carbon is crucial for feeding soil biology and driving nutrient cycles.
It acts as a glue, providing soil structure and aiding in aeration and erosion mitigation.
Soil organic carbon is significant in the context of climate change and carbon sequestration.
Soil organic carbon exists in labile and recalcitrant forms, with different stability and persistence.
Measuring soil organic carbon is essential for farming systems and potential carbon credits.
Soil organic carbon is measured using wet chemistry methods like Walkley-Black or loss on ignition.
LECO machines are used to measure carbon through combustion in soil samples.
Lab analysis provides the concentration of carbon in soil samples.
Bulk density of soil is necessary to calculate the soil organic carbon stock.
Soil organic carbon stock is vital for carbon trading and assessing carbon sequestration potential.
Monitoring soil organic carbon can improve soil health and potentially generate additional income.
Transcripts
Hi there! Some of you have been asking questions about carbon, so we wanted to give you a
brief video to basically talk through some of these things about carbon.
One of your first questions is ‘What is total carbon?’ Well total carbon is the
organic carbon and the inorganic carbon that we find in our soils. The inorganic carbon
is basically the carbonates. And when we look at a soil, and it maybe has high carbonates,
we try to remove those using acids because what we’re interested in is the organic stuff.
Now this exists as our soil organic matter and what that is, is basically former bits
of plants animals, all that dead stuff that’s turning over in our soils and also the life
that’s in our soils at the moment. But it’s really hard to measure soil organic matter, so what we
usually do is measure soil organic carbon. Now soil organic carbon is only about 40% of the
soil organic matter, so we use an estimation or approximation of our soil organic matter
based on the soil organic carbon measurements. Soil organic carbon is important because it’s the
food that feeds the biology that drives the nutrient cycles which we rely on to grow our
plants. It also acts as a type of glue, helping to stick the mineral components of our soils
together, and in doing so it gives us structure and that structure allows better aeration and also
can help mitigate some of the effects of erosion events. And I guess finally, soil organic carbon
becomes important because it’s something we hear a lot about in relation to our fight or struggle
against climate change. Our ability to put more carbon into our soils is often something we’re
encouraged to do. And this is why we might want to look at our soil organic carbon, but in our soils,
that soil organic carbon can exist in two other forms: the labile form, which is what’s feeding
that biology and driving those nutrient cycles and a recalcitrant form (which is nearer to the
inorganic often, but is more like humic substances or what we call minerally occluded carbon) and
that’s the type of carbon that’s more stable and likely to persist in our environment for longer.
So our soil organic carbon is really important to help us with a number of things we rely on
in our farming system. That said, suppose you did want to try and farm carbon or
look for carbon credits – yes you need to know what your soil organic carbon is.
So when we send our soils off to the lab to measure soil organic carbon, it’s generally
measured in one of two main ways. The first way is using Walkley-Black, which is a wet chemistry
measure. The second is using loss on ignition, and that’s often done on a machine like this behind
me – a LECO where the carbon is basically burned out of the soil and it’s measured. So this is how
it’s done and these are the results you get back from the lab analysis. Now what tells you is how
much carbon you have in a gram or in a kilogram of soil – if you like it’s giving you a percentage
of carbon in your sample. And that’s fine, but as many of us will know, when we actually think about
a field, the density of our soils in those fields is much higher than a gram per centimetre cubed
or a tonne per metre cubed -it’s bigger than that. So what we need to know is the bulk density of our
soils. We can then multiply that concentration of carbon in our soils by the bulk density in
our soils and that gives us our soil organic carbon stock. And that’s what we’re interested
in when we’re looking at carbon trading. So there you go – if you’re interested in carbon
trading or not, soil organic carbon is definitely something you want to have in your system; it’s
something you maybe want to measure and monitor in your farming systems, because just having it will
help with your soil biology, it’ll help with your soil structure, and you never know – it just might
make you a few extra pennies on the side. That’s soil organic carbon!
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