Regenerative Agriculture Promotes Soil Health by Improving Soil Structure Through Organic Carbon Storage

Soil degradation driven by inappropriate soil management is a serious global challenge, while climate change-induced yield declines are increasing the conversion of natural ecosystems to agricultural land. This review examines how soil structure influences soil health, focusing on organo-mineral complexes derived from microbial biomass and soil organic carbon-to-clay (SOC/Clay) ratio as an indicator of structural quality. Regenerative agriculture based on conservation farming practices helps mitigate SOC depletion and aligns with the nature-based solutions framework. In Hokkaido, Japan, 10 years of clean agricultural applications (cover crops and organic matter application) increased SOC storage in farmland affected by volcanic eruption. This was associated with improved bulk density, porosity, cation exchange capacity, and phosphate absorption capacity, indicating improved soil health. The increased SOC rose SOC/Clay ratio to levels comparable with unaffected farmland (≥1/13). When the SOC/Clay ratio exceeded 1/13 (soil carbon storage level of 30 t C/ha/15 cm), carbon sequestration rate became negative. This suggests that improved soil health and structural quality may promote carbon saturation and stimulate microbial decomposition of existing SOC. While the threshold for SOC/Clay ratio varies depending on soil type, vegetation type, climatic conditions, and land use, changes in the SOC/Clay ratio can provide insights into changes in soil health and structural quality.