Greenhouse Gas Emissions from an Irrigated Silt Loam Soil Amended with Anaerobically Digested Dairy Manure

Dairy production in the Pacific Northwest has grown steadily during the past decade. This increase has been accompanied by management challenges associated with production of large concentrations of dairy animal wastes that are implicated in the decline in surface and subsurface water quality as well as an increase in the production of greenhouse gases (GHG). Field studies were conducted to characterize GHG emissions from a silt loam soil planted to silage corn (Zea mays L.) amended with urea fertilizer (NPK), liquid dairy manure (LM), anaerobically digested dairy effluent (DE), or anaerobically digested fiber (DF), and unfertilized (UF) and fallow (F) treatments. Seasonal CH4 fluxes among treatments averaged −0.67 g CH4–C ha−1 d−1 in 2007 and −0.79 g CH4–C ha−1 d−1 in 2008, except at times of manure amendment. Methane emissions for 2 d after manure applications were 58-fold higher than the average CH4 uptake of the F, UF, NPK, and DF treatments. In 2007 and 2008 the N2O emitted represented 0.03 and 0.12% (NPK), 0.09 and 0.05% (DF), 0.05 and 0.10% (DE), and 0.09 and 0.11% (LM), respectively, of the total N applied during the 122-d growing season. Liquid slurry manure applications resulted in higher CH4 emissions than urea N fertilizers. Methane emissions after application were attributed to the release of dissolved CH4–C in the LM and DE slurries and not from the soil. Further research is needed to clarify GHG fluxes following manure additions during the fall and winter months.