Since the early days of soil science, protocols for fractioning of soil organic matter exist to better understand and describe the composition or turnover in soils. This remains a hotly debated topic, largely due to the persistent challenge of achieving meaningful measurements of soil carbon quality to better capture the persistence and vulnerability of carbon in soils. Unlike other soil parameters that are comparatively more straightforward to measure, the mechanisms conferring the persistence of soil organic matter in soils are far harder to isolate and quantify, and no single method will and can capture all of them simultaneously. Chemistry, density, size, thermal stability and many more intrinsic properties are used to separate soil carbon in operationally defined pools to be able to understand its (potential) persistence or functioning. For instance, by size and mechanical stability fractionation, aggregates and very stable pseudosands can be obtained for further analysis of physically protected organic matter. Moreover, a plethora of chemical and physical fractionation schemes exist to extract microbial or fungal parts to estimate their biomass, or density fractionation is applied to soils to separate particulate and mineral-associated organic matter. Despite a methodological diversity, a persistent difficulty lies in reconciling operationally defined fractions shaped by the extraction method itself with functionally meaningful, biologically or biogeochemically relevant pools in soil.
This session invites contributions focussing on methods to fractionate soil carbon in functional pools, from highly sophisticated, to novel or classical methods . We particularly welcome efforts to link laboratory-based fractions to computational modelling frameworks. Contributions that go beyond successful stories are especially encouraged: we invite submissions that reflect on fractioning not yielding the expected trends, and the exploration of the reasons behind this lacking link.