Measuring soil carbon sequestration

With the establishment of our Paulownia hybrid trees, we can not only capture carbon from the fast growth of the wood every year, but we can also increase the amount of carbon stored in the land. As with any project aiming to reduce carbon emissions, we need to be able to measure and then monitor CO2 to evaluate the impacts of different actions on the environment. It can be measured down to a square metre of earth.

As we get ready to plant our Phoenix One seedlings in our first major undertaking at Euston Estates, we have measured how much carbon there is in the soil on the fields we are preparing, to provide a baseline for our project. Using TerraMap - Omnia software gives us a snapshot of the underlying health of the soil.

TerraMap uses passive, gamma-ray detection technology to provide high-definition mapping of soil carbon alongside a range of other properties. Data is collected in the field. The raw scan, soil data and soil samples are then combined and processed to produce up to 27 high-definition soil property layers including the carbon data.

There have been some very interesting findings.

The carbon and soil map, produced by Omnia, represents just under 20% of the land we will be planting at Euston Estates in 2022. The pale blue areas indicate that there is between 0.6 - 0.9 tonnes of active carbon currently in the soil, averaging 0.84 tonnes per Ha. We are also finding that active carbon is less than 5% of all carbon matter (both active and inactive) overall. These are low readings and we would expect to see a three to five-fold increase once the trees are established. We have also found that the amount of organic matter is less than 2%, which is not unusual for actively farmed land, but is also low. Organic matter is an indication of the health and biodiversity within the soil and we would expect this to recover to 6 to 8% in the coming years.

Inactive carbon is flint or stone in the soil whilst active carbon is what is held in the soil due to actions above ground. Soil organic matter is made up of plant and animal residues in different stages of decomposition, cells of soil microorganisms, and substances that are so well-decomposed it’s impossible to tell what they were to begin with. However, the way the land is managed also affects soil organic matter level, and it is not unusual for that level to decline over time in cultivated fields. Frequent tillage, periods of bare ground, and removal of crop residues all reduce soil organic matter.

Our study does reveal low numbers for active soil carbon, but they should not come as a surprise. The agricultural land has been successfully tilled for many generations, which has a major impact on the amount of organic matter present in the soil.

The introduction of our deciduous trees, combined with an absence of traditional farm practices, will boost life in the soil and create hundreds of carbon sinks, as the root system of each hybrid paulownia tree develops. Leaf fall in the autumn combined with the mixed wild flower, legume and grass understory, will add to the richness of life beneath the soil. That will in turn support the invertebrate population that lays the foundation for greater biodiversity. Insects are the glue of ecosystems.

Now we have established the baseline for our project we will continue to measure the carbon in the coming years. We expect the active carbon to rise over time, and the land will hold more water and be richer in life. As this soil life regenerates it will increase infiltration rates reducing water runoff which can create algal blooms and cause lakes, streams and rivers to silt up.

We are preparing the land as we would for any agricultural crop, but after the trees have been planted we will leave the soil untouched, with huge benefits resulting. A stable soil will enable microorganisms to thrive and interact, with deep burrowing worms leading to increasing populations of many different forms of wildlife. Nature will do what it does best when left to its own devices. And we will continue to measure the positive, long-lasting benefits for the carbon in the soil.

Images show site preparation work underway

Nigel Couch

Managing Director, Carbon Plantations.

20th April 2022.

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