Comparison of Greenhouse Gas Emissions from Composted and Liquid Swine Manure Management Systems.

Liquid manure management systems that involve long term storing and spreading over agricultural lands have been recognized as a significant source of agricultural greenhouse gas (GHG) emissions. Composting of liquid swine manure (LSM) with straw under forced aeration has been suggested as a mitigation practice for emissions of GHGs such as methane (CH₄) and nitrous oxide (N₂O). The GHG emissions during composting of LSM with straw and the N₂O emissions after field application of composted manure versus LSM have not been directly compared in past studies.

A non-steady state chamber approach was used to measure CH₄ and N₂O fluxes during composting. The flux gradient method was used to quantify N₂O emissions from soils after fall application of composted and untreated LSM in 2004 and 2005. Measurements were carried out at Arkell, Ontario, Canada, following manure application until early summer (June) of each year, including winter and spring thaw. Gas concentrations were measured using a tunable diode laser trace gas analyzer.

GHG emissions were reduced by 35% during composting compared to LSM storage, mainly due to decreased CH₄ fluxes. Field application of compost resulted in 57% reduction of N₂O emissions during February to May in 2005 compared to application of LSM (526 vs. 1232 g N₂O-N ha^-1), but emissions during the same period in 2006 were not significantly different (589 vs. 491 g N₂O-N ha^-1). Differences between years were related to winter and spring thaw conditions. Composting of LSM with straw has the potential of decreasing soil N₂O fluxes, but this effect is related to winter conditions. However, in comparison to liquid swine manure management, aerobic composting was estimated to reduce the overall GHG emissions on a CO₂-equivalent basis by 26%.