Composting as a Strategy to Reduce Greenhouse Gas Emissions

Composting animal manure has the potential to reduce emissions of nitrous oxide (N2O) and methane (CH4) from agriculture. Agriculture has been recognized as a major contributor of greenhouse gases, releasing an estimated 81% and 70% of the anthropogenic emissions of nitrous oxide (N2O) and methane (CH4), respectively. A significant amount of methane is emitted during the storage of liquid manure, whereas nitrous oxide is emitted from the storage of manure and from soil following manure or fertilizer application. Composting animal manure can reduce GHG emissions in two ways; by reducing nitrous oxide and methane emissions during manure storage and application, and by reducing the amount of manufactured fertilizers and the GHG associated with their production and use. We will present information of GHG emissions and potentials for reduction based on available data, and on specific composting experiments. Nitrous oxide and methane emissions were monitored on an enclosed composting system processing liquid hog manure. Measurements indicated that total GHG emissions during composting were 24% of the Tier 2 IPCC estimates for traditional liquid hog manure management on that farm. Previous research has also indicated little nitrous oxide emission following application of composted manure to soil. The method of composting has a large impact on GHG emissions, where GHG emissions are higher from outdoor windrow composting systems than from controlled aerated systems. Further research is required to assess the whole manure management system, but composting appears to have great potential to reduce GHG emissions from agriculture. The bonus is that composting also addresses a number of other environmental concerns such as pathogens, surface and groundwater quality and ammonia emissions.