Trade‐offs between soil organic carbon surface gains and subsurface losses following 60 years of contrasting tillage and crop rotations

Conservation tillage and diversified crop rotations are known to enhance soil organic carbon (SOC) storage in surface soils (0–20 cm), while their long‐term effects on subsurface SOC storage remain poorly understood. This study examined the 60+ year impacts of tillage and rotation on surface and subsurface SOC storage and aggregation at the Triplett–Van Doren Experiment in Ohio, at two locations with contrasting soil types (Wooster silt loam and Hoytville clay loam). Soil cores were sampled in 2024 from the full factorial randomized complete block design including three tillage intensities (moldboard plow [MP], chisel plow [CP], and no‐tillage [NT]) and three crop rotations (continuous corn [ Zea mays L.], corn–soybean [ Glycine max (L.) Merr.], and corn–forage–forage), segmented into five depths (0–10–20–30–50–100 cm), and analyzed for SOC, particulate and mineral‐associated organic C (POC and MAOC) stocks, and mean weight diameter (MWD). Tillage and depth had greater influence on SOC stocks than rotation. In the 0‐ to 10‐cm depth, NT stored more SOC and MAOC than MP and CP at both locations, more POC at Hoytville, and had greater MWD at Wooster. At the 30‐ to 50‐cm depth, MP stored more SOC and MAOC than NT and CP at both locations. At the 50‐ to 100‐cm depth at Hoytville, MP and CP stored more POC than NT. Thus, tillage disturbed SOC in the surface soil and distributed SOC into subsurface soil depths. The depth‐dependent nature of SOC storage after six decades underscores the importance of including subsurface soils in SOC assessments.