Soil carbon changes in cultivated and excavated land converted to grasses in east-central Saskatchewan

The conversion of annually cultivated or disturbed marginal land to forage grasses has the potential to accrete soil organic carbon (SOC) in the surface 0-15 cm depth. Soil organic carbon mass (Mg ha(-1)) was measured in ten side-by-side cultivated versus forage grass seed-down restoration treatments on catenae at various sites in east-central Saskatchewan, Canada. Treatments were imposed for time periods ranging from five to twelve years. It was found that SOC mass was usually significantly higher in the grassland restorations versus the paired cultivated equivalents. Estimated SOC gain rates (0-15 cm) from grass seed-down in the region was estimated to be 0.6 to 0.8 Mg C ha(-1) yr(-1). Light fraction organic carbon (LFOC), the labile component of SOC, was more variable in the comparisons than SOC. Measured C-13 natural abundance values in selected equivalent comparisons revealed a possible contribution from seeded warm season C-4 grasses and soil carbonate C-13 to the C pools in upslope positions of the landscape. Overall, grassland restoration in this region appears to result in increased carbon storage in the surface soil.