CARBON DISTRIBUTION AND GREENHOUSE GAS EMISSIONS IN CULTIVATED AND RESTORED GRASSLAND SOILS IN SASKATCHEWAN
Nelson, Jennifer D. J.
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The impact of grassland restoration on amounts and forms of soil organic carbon (SOC)were examined using soil cores from paired cultivated and restored grassland catenae in the Missouri Coteau region of south-central Saskatchewan. Total SOC (0-15emdepth)and light fraction organic carbon (LFOC) (0-7.5 em) contents were determined in paired catenae in upland areas and in the surface (0-15cm) and at depth (> 15cm)in the wetland fringe areas. Soil organic carbon amounts were typically higher in the restored grassland catenae than in the cultivated equivalents, indicating that a switch to permanent cover on these soils will increase carbon sequestered in the soil. Shoulder positions showed the highest responses, with a 1.4-2.9 Mg ha-l yr'SOC increase over an approximately eight-year period observed at the three study sites. There was also an increase in the mass of LFOC and in the proportion of SOC comprised of LFOC associated with grassland restoration, reflective of higher recent C inputs in the grassland restoration. Once established, grasslands may be subjected to various managements such as fall burning of wetland fringe areas followed by cultivation in the spring. Under controlled environmental conditions, undisturbed soil cores collected from the wetland fringes revealed that over five weeks, the production of carbon dioxide, nitrous oxide and methane was reduced by32.5 to 1163.7 gm",0 to 247.6 gm", and 0 to 11.8 gm", respectively by the imposition of simulated burning and cultivation treatments. Possible alterations in microbial processes and/or microbial community structure as well as changes in root respiration may have occurred following the burning and cultivation, resulting in decreased gas production over the short-term. Imposition of saturated conditions to simulate spring flooding of the wetland fringe resulted in a decrease in carbon dioxide and nitrous oxide fluxes for most sites. Soil nitrate fluxes decreased with flooding, suggesting that lack of nitrate may eventually become the limiting factor for the denitrification process.