The role of grazing management in shaping soil organic matter and carbon pools in regenerative organic agriculture

Abstract Understanding how grazing and cover cropping influence soil carbon (C) pools is critical for sustainable agriculture and climate mitigation. This study evaluated soil organic matter (SOM), permanganate‐oxidizable carbon (POxC), and CO 2 mineralized across four management systems—grazing with cover crops (RGCC), grazing without cover crops (RGNCC), non‐grazed cover crop (NGCC), and no grazing without cover crops (NGNCC) at 0‐ to 10‐cm and 10‐ to 20‐cm depths over 3 years (2022–2024) on a Missouri organic ranch. A total of 2232 soil samples were collected and analyzed. Three‐way analysis of variance revealed significant year × treatment × depth interactions ( p < 0.05), indicating depth‐dependent and temporal variability in soil C. Surface soils (0–10 cm) were most responsive, with NGCC exhibiting the highest SOM (4.03 ± 0.10%) and POxC (676 ± 45 ppm), whereas RGNCC showed the lowest values, showing C depletion under grazing without cover crops. CO 2 mineralized were greatest in non‐grazed systems (NGCC: 702 ± 43 ppm; NGNCC: 992 ± 4.5 ppm) and lowest in RGNCC treatment (601 ± 21 ppm). SOM correlated positively with POxC ( p < 0.0001) but weakly with CO 2 ( p = 0.0296), while POxC exhibited a significant negative correlation with CO 2 ( p < 0.0001), suggesting stabilized labile C enhances retention and reduces mineralization. Results highlight the importance of multiyear, depth‐resolved assessments and identify POxC as a sensitive indicator of soil health. Management strategies combining cover crops, residue retention, and moderated grazing effectively enhance both stable and labile C pools, supporting microbial activity, long‐term soil fertility, and C sequestration in regenerative organic agroecosystems.