Physical protection of soil carbon stocks under regenerative agriculture

Regenerative agriculture is emerging as a strategy for carbon sequestration and climate change mitigation. However, for sequestration efforts to be successful, long-term stabilisation of Soil Organic Carbon (SOC) is needed. This can be achieved either through uplift in recalcitrant carbon stocks, and/or through physical protection and occlusion of carbon within stable soil aggregates. In this research soils from blackcurrant fields under regenerative management (0 to 7 years) were assessed. Soils from under the blackcurrant bush crop (bush (ca. 40 % of the field area)), and the alleyways between the blackcurrant crop rows (alley (ca. 60 % of the field area) were considered. Soil bulk density (SBD), soil aggregate fractions (proportions of water stable aggregates vs. non-water stable aggregates (WSA and NWSA)), soil carbon content, and carbon stability (thermally recalcitrant carbon vs. thermally labile carbon) were assessed. From this, long term carbon sequestration potential was calculated from both recalcitrant and occluded carbon stocks (both defined as stabilised carbon). Results indicated favourable shifts in the percentage of NWSA:WSA with time, increasing from 27.6 %:5.8 % (control arable field soil) to 12.6 %:16.0 % (alley soils), and 16.1 %:14.4 % (bush soils) after 7 years. While no significant (p≥0.05)) changes in whole field (area weighted average of alley and bush soils), recalcitrant carbon stocks were observed after 7 years, labile carbon stocks increased significantly (p≤0.05) from 10.44 to 13.87 t C ha−1. Furthermore, as a result of the occlusion of labile carbon within the WSA fraction, total stabilised carbon increased by 1.7 t C ha−1 over the 7 year period. This research provides valuable insights into the potential for carbon stabilisation and long-term stability prognoses in soils managed under regenerative agriculture practices, highlighting the important role which soil aggregate stability plays in the physical protection of carbon, and potential therein to deliver long-term carbon sequestration.