Greenhouse gas fluxes and budget for an annual cropping system

in the Red River Valley, Manitoba, Canada


Project Leader:  Dr. Mario Tenuta, Dept. Soil Science, Email:
Graduate Student:
  Aaron Glenn, Dept. Soil Science, University of Manitoba

Thesis Abstract:

by Aaron Glenn Although agriculture contributes significantly to national and global greenhouse gas (GHG) inventories, there is considerable control over management decisions and changes in production methods could lead to a significant reduction and possible mitigation of emissions from the sector. For example, conservation tillage practices have been suggested as a method of sequestering atmospheric carbon dioxide (CO2), however, many questions remain unanswered regarding the short-term efficacy of the production method and knowledge gaps exist regarding possible interactions with essential nutrient cycles, and the production of non-CO2 GHGs, such as nitrous oxide (N2O).

Between autumn 2005 and 2009, a micrometeorological flux system was used to determine net GHG exchange from an annual cropping system situated on clay soil in the Red River Valley of southern Manitoba. Concurrent net aerodynamic fluxes of CO2 and N2O were determined for three years. Four plots (4-ha each) were independently evaluated and planted to corn in 2006 and faba bean in 2007; in 2008, two spring wheat plots were monitored. As well, during the non-growing season in 2006-2007 following corn harvest, a second micrometeorological flux system capable of simultaneously measuring stable C isotopologue (12CO2 and 13CO2) fluxes was operated at the site.

Tillage intensity and crop management practices were examined for their influence on GHG emissions. Significant inter-annual variability in CO2 and N2O fluxes as a function of crop and related management activities was observed. Tillage intensity did not affect GHG emissions from the site. After accounting for harvest removals, the net ecosystem C budgets were 510 (source), 3140 (source) and -480 (sink) kg C ha-1 y-1 for the three respective crop years, summing to a three-year loss of  3170 kg C ha-1. Stable C isotope flux measurements during the non-growing season following corn harvest indicated that approximately 70 % and 20 – 30 % of the total respiration flux originated from crop residue C during the fall of 2006 and spring of 2007, respectively. The N2O emissions at the site further exacerbated the net global warming potential of this annual agroecosystem.