UC Berkeley

Livestock manure management accounts for almost 10% of greenhouse gas emissions from agriculture globally, and contributes an equal proportion to the US methane emission inventory.  Current emissions inventories use emissions factors determined from small-scale laboratory experiments that have not been compared to field-scale measurements.  We compiled published data on field-scale measurements of greenhouse gas emissions from working and research dairies and compared these to rates predicted by the IPCC Tier 2 modeling approach.  Anaerobic lagoons were the largest source of methane (368 ± 193 kg CH₄ hd^-1 y^-1), more than three times that from enteric fermentation (~100 kg CH₄ hd^-1 y^-1).  Corrals and solid manure piles were large sources of nitrous oxide (1.5 ± 0.8 and 1.1 ± 0.7 kg N₂O hd^-1 y^-1, respectively).  Nitrous oxide emissions from anaerobic lagoons (0.9 ± 0.5 kg N₂O hd^-1 y^-1) and barns (10 ± 6 kg N₂O hd^-1 y^-1) were unexpectedly large.  Modeled methane emissions underestimated field-measurement means for most manure management practices. Modeled nitrous oxide emissions underestimated field-measurement means for anaerobic lagoons and manure piles, but overestimated emissions from slurry storage.  Revised emissions factors nearly doubled slurry CH₄ emissions for Europe and increased N₂O emissions from solid piles and lagoons in the US by an order of magnitude. Our results suggest that current greenhouse gas emission factors generally underestimate emissions from dairy manure and highlight liquid manure systems as promising target areas for greenhouse gas mitigation.