Effects of winter storage conditions and subsequent agitation on gaseous emissions from liquid dairy manure

Abstract

An understanding of emissions from liquid manure facilities during winter, spring thaw and agitation is needed to improve national emissions inventories in Canada. In this study, liquid dairy manure was stored in six pilot-scale tanks (1.8 m deep × 6.6 m2 surface area) covered by steady-state chambers that enabled greenhouse gas (GHG) and ammonia (NH3) flux measurement. After 158 d of undisturbed storage, three tanks were agitated for 5 d (8 h per day) consecutively. During storage, methane (CH4) flux was correlated with manure temperature at 30 cm depth (P < 0.05). Nitrous oxide (N2O) fluxes occurred only during spring thaw - at rates comparable with agricultural soil during spring thaw. On a carbon dioxide (CO2) equivalent basis, however, cumulative N2O fluxes were negligible compared with CH4 fluxes. Flux of NH3 was correlated positively with manure temperature near the surface and negatively with the presence of ice or a surface crust (P < 0.01). Agitation did not affect N2O and NH3 fluxes, whereas CO2 and CH4 fluxes increased significantly (P < 0.01) as dissolved gas and bubbles were released. Trapped CH4 released during agitation was estimated to be 6.3 g CH4 m-3 manure, and was depleted in 2 d. Considering the entire storage period, agitated tanks (158 d + 5 d agitation) had 6% higher GHG fluxes due to higher CH4 losses than undisturbed tanks (163 d). This CH4 release is small in context of annual fluxes, but may partially explain discrepancies between predicted and measured winter fluxes.Key words: Manure storage, agitation, greenhouse gas emission, ammonia emission, dissolved gas