Carbon Distribution and Greenhouse Gas Emissions in Cultivated and Restored Grassland Soils in Saskatchewan
Nelson, J. D.. 2002. M.Sc. Thesis. Dept. Soil Science, University of Saskatchewan, Saskatoon, SK
Abstract
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 (0-15
cm depth) and light fraction organic carbon (LFOC) (0-7.5 cm) 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-1yr-1
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 by 32.5 to 1163.7 g m-2
, 0 to 247.6 g m-2
, and 0 to 11.8 g m-2
,
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.
