Can occasional ploughing enhance soil organic carbon stabilization?

A soil’s capacity to store and stabilize organic carbon (OC) is commonly attributed to its silt and clay content, which provides mineral surface area for OC interactions. Because this surface area is finite, soils are assumed to exhibit a texture-dependent limit for OC stabilization, referred to as soil OC saturation. However, this concept neglects the role of soil structure, which largely determines which mineral surfaces are actually accessible for contact with OC.

In structured soils, OC predominantly enters through soil pores. In the absence of structural turnover, these pores may represent sites of high OC content where mineral surfaces are saturated. Meanwhile, other parts of the soil matrix do not receive OC input and therefore remain well below their OC storage capacity. Based on this assumption, we hypothesize that the occasional ploughing of agricultural fields may eventually increase net soil OC stabilization. Specifically, the infrequent disruption of the soil structure could redistribute the OC more evenly throughout the soil matrix, thereby bringing previously unsaturated mineral surfaces into contact with OC.

We investigate this hypothesis by monitoring OC stocks and soil respiration (used as a proxy for OC turnover and stabilization) over several years in intact soil samples from agricultural fields that had been subjected to a single ploughing event after more than a decade. These were then compared with non-ploughed control fields. Initial results show that ploughing led to a redistribution of predominantly surface-stored OC (0-5 cm) throughout the entire plough horizon (0-20 cm). This initially resulted in increased soil respiration and microbial activity in the middle of the plough layer (10-15 cm), accompanied by a decrease in the OC content at the soil surface. After seven months, soil respiration declined, indicating the onset of OC stabilization processes. Analyses of disturbed soil samples from the same sites suggest that the physical disruption of soil structure itself played a minor role compared to the OC redistribution.

These results demonstrate that a single ploughing event can induce not only short-term OC destabilization, but also longer-term stabilizing effects, in line with our hypothesis. Ongoing and planned analyses will further assess the temporal development of OC stocks, stabilization processes, and the spatial distribution of OC within soil microsites.