Over a decade of minimum tillage: Impacts on soil organic carbon stocks to 70 cm depth in selected East Danish farmer fields

Minimum tillage (MT) practices have gained increasing attention for their potential role in climate change mitigation. However, in temperate regions, studies examining the full soil profile have shown limited or no significant soil organic carbon (SOC) accumulation with MT practices. This study collected soil samples from fields managed by some of Denmark's most experienced MT practitioners and paired them with adjacent conventional tillage (CT) fields. Each MT/CT pair was located within the same geophysical conditions and under similar crop rotations, minimising the risk of confounding variables unrelated to tillage. The results show a strong positive linear correlation (R² = 0.73) between the duration of MT management and the SOC stock difference between paired MT and CT fields across the full 0–70 cm soil depth, suggesting that long-term MT practices may enhance SOC sequestration over time. A more sequential data analysis supported other published works that SOC accumulation in MT fields was primarily confined to the upper 0–10 cm layer, while CT fields exhibited higher SOC stocks in the 10–30 cm layer. No significant differences in SOC were observed below 30 cm. When averaging these numbers across the 0–70 cm profile, SOC stocks did not differ significantly between the tillage systems. Despite limited availability of fields with more than a decade of MT management history farmers' fields serve as valuable, real-world laboratories for understanding the long-term impacts of tillage on SOC dynamics. A scalable pairing methodology is proposed with larger sample sizes in the range of 30–50 paired fields for achieving statistical robustness across heterogeneous agricultural landscapes. • Regression on paired MT/CT fields shows cumulative SOC effects at 0–70 cm depth. • Crossfield SOC comparisons without pairing can mislead due to soil heterogeneity. • Geoecological mapping helps identify MT/CT pairs with similar soil conditions. • This scalable approach supports future SOC hypotheses with larger sample sizes.