Three ways new tech aims to improve soil carbon estimates – Farmers Weekly
How do you measure soil carbon both accurately and affordably at scale? ...
Measuring soil organic carbon accurately has always been difficult. But with the rise in interest in carbon trading in agriculture, as well as the other benefits from managing carbon stocks in soils, companies are looking at alternative methods of measuring soil organic carbon that meet the key criteria of accuracy and affordability.
Robust measurement of soil carbon stocks – total soil carbon, not just soil carbon percentage – and how it changes over time is critical to providing evidence to governments, food businesses and other corporates that soils really are removing carbon dioxide from the atmosphere and storing it.
Techniques being developed to provide that evidence include sensor technology, improving the throughput and accuracy of physical soil sampling, and advanced data analytics.
Scanning for soil emissions
Hutchinsons TerraMap Carbon service uses a metre-long, tube-like passive sensor usually fitted to a lightweight all-terrain vehicle to pick up gamma radiation that is naturally emitted from soils.
A scaled-down version of sensors fitted to aircraft and used for mineral prospecting, the technology has been developed for agriculture by Canadian company SoilOptix, explains Matt Ward, Hutchinsons services leader.
“It senses four naturally occurring radioactive isotopes – caesium, potassium, thorium and uranium, which, depending on the levels of each, infers different soil characteristics.”
Ground truthing
Once the field has been scanned, typically at 10-12mph in 12m swathes using a scanner height of 60-70cm, an algorithm in the service software pinpoints five to eight locations in the field for ground truthing soil samples. The resulting lab analysis is then used to generate a map using the variation detected by the field scan.
The technique can be used to map all common nutrients, pH, soil texture, organic matter, cation-exchange capacity, elevation, plant-available water, as well as both total organic carbon and active carbon – the percentage that is actively cycled in the soil.
The scanner measures carbon to a depth of 15cm in the soil profile. Initial research with Adas and Niab when the service launched in 2021 suggested there was little difference in carbon depending on soil depth, but that’s being revisited this year, with an aim to measure to 30cm depth. “Realistically, that’s the most you can sensibly influence through soil management,” Mr Ward suggests.
Maps are viewed and analysed within Hutchinsons’ Omnia platform, which enables fields to be compared using a fixed or dynamic colour scale. The fixed scale prevents showing variation when, in reality, there isn’t much, Mr Ward says. The dynamic view divides each field into 10 different zones, from the highest to lowest levels.
Organic matter:clay ratio
Omnia uses scientific research demonstrating threshold ratios for soil organic carbon to clay content for different levels of soil condition to help farmers interpret results, creating a map that shows areas of the farm with degraded, moderate, good or very good soils. “It helps farmers see which fields are actually good and which are not and start to focus activities.”
The standard service, which includes measurement of phosphorus, potassium, magnesium, pH, percentage of sand, silt and clay, elevation plus organic matter, costs £30/ha, and the standard carbon service, which also includes percentage and total organic carbon, costs £37/ha, Mr Ward says.
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