Persistence of Soil Organic Carbon after Plowing a Long‐Term No‐Till Field in Southern Ontario, Canada

There is abundant evidence that minimizing soil disturbance reduces mineralization of organic matter and can result in larger storage of soil organic carbon (SOC) relative to conventional tillage. However, little is known about the persistence of SOC when no‐till lands are plowed periodically. This study set out to determine the change in SOC when a long‐term (22 yr) no‐till field in southern Ontario, Canada, was plowed once. Four plots were located within three textural classes [sandy loam (SL), sandy clay loam (SCL), and silty clay loam (SiCL)] within two hydrologic conditions (well‐ and poorly drained) in the field. The plots were sampled before and three times after (3 d, 7 mo, and 18 mo) the no‐till field was moldboard plowed. The single tillage event homogenized the SOC through the profile and reduced the stratification. When calculated on an equivalent mass basis beyond the plow depth, there was no significant change in SOC 18 mo after plowing the SCL, SiCL, and SL high SOC plots. However, in the SL plot with low SOC, there was a loss of about 3 Mg SOC ha −1 after 18 mo, and the loss occurred primarily between the 15‐ and 30‐cm depths in the profile. The loss may have accounted for as much as two‐thirds of the SOC gained from no‐tillage. This study also emphasized the need for additional care to account for changes in bulk density when comparing the quantity of soil constituents, such as SOC, after plowing.