Early evidence for the benefits of biochar in organic regenerative agriculture

Enhancing soil carbon stocks is important to improve soil quality, but also plays a crucial role in mitigating climate change. The potential of innovative approaches such as regenerative farming practices for increasing soil organic carbon (SOC) needs to be explored. A randomized block experiment was established on an organic farm in Hesse, Germany, to assess the effects of different regenerative agricultural (RA) practices on SOC stock changes over a period of three years (2020-2023). The treatments included minimum tillage combined with cover and nurse crops (RA), RA practices plus the incorporation of biochar (BC) at 30 cm depth with a subsoil loosening device (RABC) and conventional soil cultivation with ploughing and moderate cover cropping as a control. In the beginning and at the end of the experiment, intact soil cores were extracted down to 100 cm depth with a percussion corer and divided into five depth increments for analysis to evaluate changes in SOC stocks. The RABC treatment resulted in the highest increase in native SOC (+ 2.24 Mg C ha^-1 over three years), in addition to the applied biochar carbon (2.2 Mg C ha^-1), compared to the control. In contrast, RA alone did not significantly alter SOC stocks compared to the control. Changes in bulk density played a key role in the observed SOC stock differences, with RABC showing the strongest reduction, particularly in deeper layers. Early indicators of SOC stock changes, such as CO₂-C respiration, water-extractable organic carbon (WEOC), and water-extractable organic nitrogen (WEON), showed positive trends favoring RA and RABC, but effects were not statistically significant. Microbial Biomass Carbon (MBC) in the 0-10 cm soil layer was the strongest early indicator, significantly increasing in both RA and RABC compared to the control. These findings highlight that RA practices, particularly when combined with biochar application in the subsoil, improve soil structure in the early phase after management change and may enhance SOC stocks. However, field experiments lasting more than a decade and full carbon balance assessments are required to evaluate the overall C (CO₂eq-)sequestration potential and climate mitigation effects including non-CO₂ greenhouse gas fluxes.