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 (CH), carbon dioxide (CO), nitrous oxide (NO), and ammonia (NH) 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 NO and CH with most carbon being emitted as CO-C and most N emitted as NH-N. Compost storage had higher CH and NO emissions than the active phase, while NH was emitted at a lower rate, and CO was similar. Overall, combining both the active composting and storage phases, the mean total emissions were 3.9×10gCHkg raw manure (RM), 11.3gCOkg RM, 2.5×10g NO kg RM, and 0.13g NH kg 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 (CH+NO) from solid separation, composting, compost storage, and separated liquid storage were reduced substantially on a CO-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 NH was emitted at higher rates from the continuously turned composter than reported values for traditional storage.