It seems nothing escapes the scrutiny of scientists when it comes to greenhouse gas emissions. A team of researchers from the University of Saskatchewan recently completed an investigation of greenhouse gas emissions on Saskatchewan rangelands.
The major greenhouse gases – carbon dioxide, nitrous oxide and methane – have always been produced naturally as a result of normal biological processes. However, changes to the environment as a result of human activities can shift the balance of natural controls on these processes. Disruption of natural controls on greenhouse gas production can lead to an increase in production of these gases.
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According to Agriculture Canada, primary agriculture contributes approximately 10 percent of Canada’s greenhouse gas emissions. Rangelands, like other natural systems, will produce greenhouse gas to some extent. Determining the magnitude of greenhouse gas emissions from rangeland will help Canada comply with its emission reduction targets, according to Yuguang Bai, project leader and associate professor with the
U of S plant science department.
“GHG emissions from rangelands, especially those with hummocky terrain, are understudied, possibly due to complex interactions of landform elements, physical characteristics, disturbance and plant community, all of which vary in space and time,” he said.
“The objectives of this study were to contrast the spatial variability of GHG emissions between protected and defoliated rangelands, to model landscape-level variations in GHG emissions and to correlate GHG (emissions) with landscape elements, biophysical factors, plant species diversity and forage production.
In addition, we wanted to determine the relationship between range condition and soil carbon, as well as the effect of shrub invasion on soil carbon. Finally, we hoped to provide baseline data for optimal pasture management to maximize economic and ecological returns.”
To achieve this, Bai and his colleagues conducted three experiments in central and southern Saskatchewan between 2003 and 2005. The areas covered the mixed grassland and moist mixed grassland ecoregions.
A number of landform elements were looked at, such as the north-facing concave aspect, the north facing convex aspect, the south facing concave aspect, level upland and depression, within hummocky landscapes.
“We applied a defoliation treatment in April to simulate grazing, among other things, and we measured carbon dioxide and other gas emissions every seven to 10 days, from spring until fall, with chambers designed specifically for this purpose,” Bai said.
“We found that particular landscape elements significantly affected the flux of carbon dioxide and nitrous oxide. We also found that biophysical characteristics, such as soil temperature and water content, as well as plant species composition, also varied among landscape elements, contributing to variations in GHG fluxes. The greatest GHG flux was found in the depression. Mowing increased the positive flux of carbon dioxide and nitrous oxide while increasing the negative flux of methane.”
The scientists also studied the effect of shrub invasion on soil carbon in nine sites. Results showed that, along a gradient from grassland to shrub communities, soil organic carbon had a less than five percent increase. Effectively, there was no significant difference in soil organic carbon between the different plant communities.
Another nine sites were selected to study the effect of cattle grazing on soil carbon. Investigation revealed that grazing did not significantly affect soil organic carbon. The researchers found that soil carbon was controlled more by soil texture than by shrub cover or grazing, with loamy soils having greater soil organic carbon and root biomass than sandy soils.
“Overall, the mixed prairie of Saskatchewan likely contributes very little to GHG emissions,” Bai said.
“Properly managed, the mixed grass prairie has a well-balanced nutrient cycle that includes various greenhouse gases. The grassland ecosystem plays a role in mitigating climate change by retaining carbon that would otherwise be released into the atmosphere if poor grazing management or conversion to arable agriculture occurred.”
