Enhanced rock weathering can help soils sequester carbon indefinitely

ENHANCED rock weathering is a nature-based carbon removal technology that permanently locks away carbon dioxide from the atmosphere. This geological process has happened naturally for millions of years – enhanced weathering simply speeds it up so that the whole process takes place in a matter of decades.

However, by adding fine weathered aggregate to soil and by boosting soil organic matter production, regenerative farmers can potentially grow soil and soil carbon indefinitely.

UNDO is a UK based company that specialises in enhanced rock weathering. Speaking to 8.9ha News, Jennifer Brodie, UNDO’s Business Development Manager for Scotland, said “There is this conception that soil has a limited ability to capture carbon, but soil is a growing, living media. When we add rock, that’s adding the minerals, but it is also boosting the life in the soil. It is a catalyst to grow our soil. Soil used to be much deeper and we need to get back to growing our soil.”

In the context of agroecology this is important. In regenerative livestock management systems the growth in soil organic matter can be substantial – as we reported earlier this week Gabe Brown built 29 inches of soil in a decade – but when new fine aggregate is added to organic matter the result can be a new, indefinite supply of robust, carbon rich and resilient soil.

Jennifer Brodie said “We’ve been dependent on NPK fertilisers which have made the plants grow fast but weak, so we’ve had to add pesticides and herbicides, which has killed the life in our soil. The enhanced rock weathering that we’re adding at the moment, it boosts the life in the soil and we can climb our way back out; we can grow our soil, and it can go on indefinitely.”

For millions of years, carbon dioxide has combined with rainwater to form carbonic acid. When this dilute acid falls on mountains, forests and grassland, the CO2 interacts with the rocks and soil, mineralises and is safely stored in carbonate form. However, natural rock weathering takes hundreds of thousands of years.

UNDO says on its website that they “enhance and accelerate this process by spreading crushed basalt rock on farmland, increasing the surface area of the rock and giving it immediate contact with the CO2 produced by plant roots and soil microbes.”

UNDO applies its enhanced rock weathering process specifically to basalt, an igneous volcanic rock that forms when molten lava cools. The company says that basalt is “highly reactive, weathering quickly to speed up the sequestration of CO2. Basalt is safe to use and offers significant co-benefits for crop and soil health.”

The basalt used for enhanced rock weathering is essentially a waste product, and as a result the process can be scaled without additional quarrying impact. “The basalt we use is an existing by-product of aggregate and mining industries so we aren’t using any additional energy to procure it. It’s also the most abundant rock on earth, enabling us to scale our operations considerably.”

Business development is currently focussed on Scotland, Northern England and the USA. The company has chosen these areas as they’re close to basalt quarries, helping to minimise the emissions and costs associated with transporting the rock fines to nearby farms.

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