Greenhouse gas emissions from pig slurry during storage and after field application in northern European conditions

Different mitigation techniques for greenhouse gas (GHG) emissions from pig slurry in storage and after field application were evaluated and specific emissions factors derived. Fluxes of methane (CH4) and nitrous oxide (N2O) were measured for one year in a pilot-scale storage plant comparing uncovered pig slurry (NC) with slurry covered by straw (SC) or plastic sheet cover (PC). In spring and autumn, stored slurry was band spread (BS) in the field without or with immediate incorporation by harrowing (BS + HA). Closed chamber techniques were used for gas sampling. Complementary soil core experiments in the laboratory examined the influence of soil moisture and temperature on emissions from slurry application. Annual CH4 emissions (g CH4-C kg−1 VS) from storage were 5.3 for NC, 5.8 for SC and 2.8 for PC, corresponding to CH4 conversion factors (MCFs) of 2.6, 2.8 and 1.4%, respectively. N2O emissions from storage were low except from SC, where they comprised 31.7 g N2O-N m−2 year−1, corresponding to an N2O emissions factor (image) of 0.66% of total N (Tot-N) in slurry. N2O emissions after field application varied depending on soil conditions, with soil moisture content having a significant influence according to soil core experiments. Overall, cumulative N2O-N emissions in spring were 1.35% of Tot-N in slurry for BS and 0.46% for BS + HA. Corresponding N2O-N emissions in autumn were 0.77 and 0.97%. The MCFs observed in storage were considerably lower than the default IPCC value of 10%, while image was in the suggested IPCC range for storage and field.