Greenhouse gas emissions from pig slurry applied to forage legumes on a loamy sand soil in south central Manitoba

Information regarding the greenhouse gas (GHG) emissions resulting from the application of pig slurry to forage in western Canada is limited. This study examined the effects of addition of pig slurry and soil water content with landscape position on nitrous oxide (N2O) and methane (CH4) emissions from forage legumes [sainfoin (Onobrychis viciifolia) and alfalfa (Medicago sativa)] on a sandy loam soil in Brandon, Manitoba, over two growing seasons. Pig slurry was surface applied with a rolling aerator-type tine at a rate of 35 000 L ha(-1) and 38 000 L ha(-1), providing 62-15-50 and 205-45-86, actual N-P-K kg ha(-1), in 2006 and 2007, respectively. Emissions were measured on and between surface bands of the slurry applied to soil. Soil concentrations of NH4+ -N and NO3- -N, moisture, and temperature were also monitored. In both years, slurry application increased growing season cumulative N2O emissions. Net increase in cumulative N2O-N emissions with slurry treatment ranged from 0.04 to 0.05% of total N ha(-1)Z applied in 2006 but from 0.7 to 0.9% in 2007. The coherence of rapidly increasing N2O emissions following slurry application with decreasing soil NH4+ and increasing NO3- concentration, in combination with the fact that emissions continued even when soil NH4+ concentrations were undetectable, suggest nitrification and denitrification were sources of N2O. Emissions of CH4 were generally slightly negative and unaffected by addition of slurry. Higher soil water content at lower landscape position did not affect emissions of CH4 but did increase those of N2O in 2007. The current study was conducted at one field location. Examination of slurry additions to additional sites is required for reliable estimation of N2O emissions from slurry applied to perennial legume forages in prairie Canada.