Rock-Eval® thermal analysis as a tool to characterize SOM under different amendment contexts: four case studies

To achieve net-zero CO₂ emission by 2050, initiatives like “4 per 1000”, launched in 2015, promote actions to enhance carbon sequestration in soils. Applying organic amendment effectively raises soil organic matter (SOM) content, modifying the stability of carbon pools according to the amendment type, soil properties and environmental conditions. Sustained SOM increase depends on expanding the stable carbon pool via the addition of recalcitrant OM and/or SOM stabilization through its interaction with mineral phases. Over the past two decades, thermal analysis has emerged as a widely used approach for characterizing SOM stability, providing a proxy for its chemical recalcitrance and persistence. The Rock-Eval® method employs an open-system of successive pyrolysis and oxidation phases, during which carbon-based gases (hydrocarbon, CO and CO₂) are quantified. These emissions provide quantitative and qualitative parameters that help assessing SOM dynamics over time by distinguishing thermal carbon pools.

Four cases studies will be used to illustrate the response of SOM thermal properties to organic amendment under different contexts: (1) variation of carbon pools upon treatments with different organic amendments from a plant trial conducted in a growth chamber, (2) biochar amendment in a technosol in urban context in France, (3) geological coal pollution on a soil in Canada and (4) pyrolyzed material addition under archaeological context (Terra Preta) in Cameroon, Brazil and Bolivia. The thermal properties of these amendments will be discussed and compared.