Greenhouse Gas Emissions from Annual-alone and Annual-Perennial Cropping Systems in the Red River Valley, Manitoba

Perennial crops may increase carbon sequestration and reduce nitrous oxide emissions. Therefore, integrating perennials in rotation with annual crops could 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. The study was carried out to evaluate the benefits of including perennial forage in rotation with annual crops in terms of cumulative carbon dioxide and nitrous oxide emissions over several years. The study was done in the clay soil of the Red River Valley, at Trace Gas Manitoba (TGAS-MAN) research site at Glenlea, Manitoba. The field experiment consisted of four four-hectare plots. All four plots were planted with corn in 2006 and faba bean in 2007. In 2008, grass-alfalfa forage was introduced to two plots and grown until 2011 whereas the other two plots were planted to annual crops: spring wheat, high erucic acid rapeseed, barley and hard red spring wheat in 2008, 2009, 2010 and 2011, respectively. We continuously monitored carbon dioxide and nitrous oxide fluxes from all four plots using the micrometeorological flux-gradient method and a tunable diode laser analyzer. The results to date indicate that over six years (2006-2011), the system that included grass-alfalfa forage increased carbon uptake by 4.5 tonnes C ha-1 and decreased nitrous oxide emissions by 14 kg N ha-1 compared to the annual-alone system. After accounting for harvest removals, annual-alone and annual-perennial systems were net source of GHG by the magnitude of 28 and 15 tonne CO2-eq ha-1, respectively. From 2012 onward, all four plots will be planted with the same annual crop and greenhouse gas emission will be measured for two additional years. The two cropping systems will be compared for eight years of cropping cycle to better understand the long-term benefit of including perennials in cropping systems to reduce net greenhouse gas emissions.