Relationship Between Dairy Slurry Total Solids Levels and Greenhouse Gas and Ammonia Emissions.

Manure slurry storages are sources of greenhouse gases (GHG’s) and ammonia (NH₃) emissions. Total solids (TS) is an indicator of the volatile solids (VS) and nitrogen content which are important variables driving methane (CH₄) and NH₃ emissions, respectively. The TS content also influences the formation of natural surface crusts which may affect the magnitude of CH₄ and NH₃ emissions and induce the production of nitrous oxide (N₂O). A trial was conducted at a site located in Truro Nova Scotia, Canada to examine the effect of slurry TS level on crust formation and gas emissions. Methane, N₂O and NH₃ emissions were continuously measured from six pilot-scale storage systems over a 180 d undisturbed period from May through November, 2010. Each cell was permanently fitted with a flow-through steady-state chamber, that enclosed the entire slurry surface area and through which air was drawn continuously. Each cell was batch loaded with ~10.5 m³ of dairy slurry at a different TS level ranging from 0.3% to 9.5%. Crust formation on the slurries was variable and influenced by TS. Complete surface crust coverage only developed on the 3% < TS < 6% slurries, and only for the last 3 months of the storage period. Nitrous oxide was a minor contributor to the overall GHG budget (as CO₂-eq), representing < 5% of the total for all TS levels. Total CH₄ emissions (as kg m^‑3) increased linearly as a function of TS (E_CH4,V = 2.5 + 0.6*TS). Total NH₃ emissions (as g m^‑2) also increased linearly with TS (E_NH3,SA = 73 + 30*TS). The linear responses of CH₄ and NH₃ emissions was observed despite variable crust formation across TS levels, suggesting that the source strength of substrates for production reactions is the more important regulator of emissions.