Greenhouse gas and ammonia emissions from production of compost bedding on a dairy farm.

Recent developments in composting technology enable dairy farms to produce their own bedding from composted manure. This management practice alters the fate of carbon and nitrogen; however, there is little data available documenting how gaseous emissions are impacted. This study measured in-situ emissions of methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O), and ammonia (NH3) from an on-farm solid-liquid separation system followed by continuously-turned plug-flow composting over three seasons. Emissions were measured separately from the continuously-turned compost phase, and the compost-storage phase prior to the compost being used for cattle bedding. Active composting had low emissions of N2O and CH4 with most carbon being emitted as CO2-C and most N emitted as NH3-N. Compost storage had higher CH4 and N2O emissions than the active phase, while NH3 was emitted at a lower rate, and CO2 was similar. Overall, combining both the active composting and storage phases, the mean total emissions were 3.9×10-2gCH4kg-1 raw manure (RM), 11.3gCO2kg-1 RM, 2.5×10-4g N2O kg-1 RM, and 0.13g NH3 kg-1 RM. Emissions with solid-separation and composting were compared to calculated emissions for a traditional (unseparated) liquid manure storage tank. The total greenhouse gas emissions (CH4+N2O) from solid separation, composting, compost storage, and separated liquid storage were reduced substantially on a CO2-equivalent basis compared to traditional liquid storage. Solid-liquid separation and well-managed composting could mitigate overall greenhouse gas emissions; however, an environmental trade off was that NH3 was emitted at higher rates from the continuously turned composter than reported values for traditional storage.

The Extent of Manure Removal from Storages and Its Impact on Gaseous Emissions.

Manure remaining in storage due to incomplete removal is a source of microbial inoculum that may affect methane (CH), nitrous oxide (NO), and ammonia (NH) emissions during subsequent storage. Manure removal was studied by loading fresh manure into outdoor concrete tanks (10.6 m) that contained previously stored manure (inoculum) at six levels (0, 5, 10, 15, 20, and 25%, with 0% representing an empty tank). Emissions were continuously measured for 6-mo storage periods (warm and cold seasons) using flow-through chambers. Fluxes during the warm season (average manure temperature at 80 cm depth, = 17°C) were 25 times higher for CH, 20 times higher for NO, and 2.9 times higher for NH compared with the cold season ( = 4°C). Cumulative CH emissions increased linearly with the level of added inoculum in the cold season ( = 0.98). A similar linear increase was observed in the warm season from 0 to 20% inoculum ( = 0.91), after which a decrease in emissions was observed at 25%. Reducing inoculum from 15 to 5% reduced CH emissions by 26% in the warm season and 45% in the cold season. There was no clear effect of inoculum on NO and NH emissions, suggesting that complete manure storage emptying does not alter their emissions.