Greenhouse gas emission benefit of including
perennial forage in a Canadian Prairie cropping system Inclusion of forage perennial crops is commonly used in organic and rarely used in conventional production systems on the Canadian Prairies. Perennial crops may increase carbon sequestration and reduce nitrous oxide emissions, and could be a promising option to reduce agriculture’s contribution to greenhouse gas emissions. However, very little is known about the greenhouse gas emission benefits of including perennial forages in Canadian Prairie cropping systems. Further, it is not understood if increased carbon mineralization and nitrous oxide emissions after termination of perennial crops outweigh the emission benefits prior to termination. The objective of this study was to evaluate short-term and long-term benefits of including perennial forage in rotation with annual crops in terms of cumulative carbon dioxide and nitrous oxide emissions. The experiment is being conducted south of Winnipeg in the clay soil of the Red River Valley.The field experiment consists of four four-hectare plots. Two plots had annual crops from 2006-2011 while two plots included a grass-alfalfa foragephase from 2008 to 2011. We continuously measured carbon dioxide and nitrous oxide fluxes from all four plots using a micrometeorological flux-gradient method with a tunable diode laser analyzer. The results to date indicate that in three years (2008-2011) the system with grass-alfalfa forage increased carbon uptake by 4 tonnes C per hectare and decreased nitrous oxide emissions by 10 kg N per ha compared to the annual cropping system. However, the carbon sequestered during the alfalfa growth phase is starting to be released back to the atmosphere since its termination in the fall of 2011. Emissions will be continued to be measured and net greenhouse gas budget after accounting for harvest removal will be compared to better understand the short-term as well as long-term benefit of perennials in terms of net greenhouse gas emissions. Key words: Alfalfa, annual cropping, flux gradient method, grass, greenhouse
gases, perennial cropping
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