The misconception of soil organic carbon sequestration notion: when do we achieve climate benefit?

Abstract

Soil organic carbon (SOC) sequestration is a key function of natural and semi‐natural ecosystems. Restoring this property in terrestrial ecosystems has become central to the EU's climate change mitigation and adaptation strategies. However, SOC sequestration is a widely misunderstood concept. The different methodological approaches used to investigate and compare SOC stock under sustainable agricultural practices play a key role in reinforcing misconceptions about this complex process. This commentary paper aims not only to provide a clear definition of SOC sequestration, but also to interpret the results that can be obtained for SOC stock change estimation using the SOC stock difference and the pair comparison methods, as well as to identify the soil carbon‐related processes that achieve climate mitigation. SOC sequestration can be defined as the progressive increase in a site's SOC stock compared to pre‐intervention via a net depletion and transfer of atmospheric CO2 into the soil, where it is retained as soil organic matter (SOM), by plants, plant residues or other organic solids such as the material derived from the organic fraction of farming solid waste, which can be used as a fertilizer (e.g., manure, compost, biochar, digestate), and that is produced or derived from that land‐unit. To date the most appropriate way to determine if a land unit's soil is a sink or rather a source of atmospheric CO2 is to implement the SOC stock difference method, provided the non‐occurrence of carbon exchange between ecosystems.