Impact of Ridge Tillage on Organic Carbon Sequestration in a Clay Loam Soil in Southwestern Ontario.

Differences in traffic and tillage intensity among positions in ridge tillage (RT) create distinctly different soil environments relative to no-tillage (NT) and mouldboard plow tillage (MP), which would likely be manifested in differences in soil organic carbon (SOC) and other soil properties over time. In this study ridges were re-formed every two years (during the corn year) at 76 cm spacing and corn was planted in the center of the ridges whereas soybean was planted at 38 cm spacing. We collected soil samples from the top of the ridges (i.e. corn row), from the shoulder positions of the ridges and from the interrow positions of the ridges to evaluate both the spatial and profile distribution of SOC and selected soil physical properties under RT relative to NT and MP. After 29 years, RT decreased soil penetration resistance and bulk density in surface soil (0–5 cm) relative to NT, and significantly increased SOC stock within the plow layer relative to MP. A striking finding is that ridging practices led to a strong spatial heterogeneity in SOC, soil water content and soil penetration resistance. Ridging produced the lowest SOC in interrow and the highest SOC in row of the ridges, with medium SOC content in the shoulder. Soil water content was notably higher in the interrows than in the rows of the ridges, while soil penetration resistance followed the opposite trend. Another remarkable finding is that spatial heterogeneity in SOC did not occur in the 10- to 20-cm depth soil. Our results also illustrated that a RT sample collected in shoulder of the ridges could represent the average of samples collected across a ridge tilled field. Hence, relative to NT and MP, RT shows benefits in improving the quality of the Brookston clay loam soil in Southwestern Ontario and consequently is a feasible minimum-tillage option.