Impact of ridge tillage on soil organic carbon and selected physical properties of a clay loam in southwestern Ontario

► Long-term ridge tillage impacts on selected soil properties were examined. ► Ridge tillage resulted in strong lateral variation in selected soil properties. ► Ridge tillage decreased surface soil penetration resistance relative to no-tillage. ► Ridge tillage decreased bulk density in surface soil compared to no-tillage. ► Ridge tillage had greater soil organic carbon stocks relative to mouldboard plow. Ridge tillage (RT) creates a distinctly different soil environment relative to no-tillage (NT) and mouldboard plow tillage (MP), which may in turn affect soil properties. In this study, the impacts of long-term (29 years) RT on soil organic carbon (SOC), water content, bulk density and penetration resistance were compared with NT and MP tillage on a clay loam soil under a corn (Zea mays L.)–soybean (Glycine max L. Merr.) rotation. The ridges in RT were formed at 76-cm spacing and corn was planted in the center of the ridges whereas soybean was planted in the shoulders of the ridges at 38-cm spacing. Soil samples were collected from the ridge crest (i.e. corn row), from the two ridge shoulder positions and from the interrow (furrow) positions of the ridges to evaluate both the spatial and profile distributions of the selected soil properties under RT relative to NT and MP. Ridge tillage produced low SOC in the interrows, high SOC in the crests and medium SOC in the shoulders relative to MP and NT. Soil water content was higher in the interrows than in the crests of the ridges, while soil penetration resistance followed the reverse trend. No-tillage resulted in a distinct SOC stratification with significantly higher SOC in surface soil and slightly lower SOC in subsurface soil while a uniform distribution of SOC was observed in the plow layer of MP soil. Hence, RT produced different SOC, water content, bulk density and penetration resistance distributions than NT and MP. Twenty-nine years of RT management resulted in improved soil physical conditions in the plow layer for crop root growth relative to NT and greater SOC stocks within the plow layer compared to MP.