Meta-analysis of greenhouse gas and ammonia emissions from dairy manure composting

In order to minimise nutrient losses, comprehensive overviews of the magnitude of gaseous emissions from manure composting processes and the factors that influence these losses are urgently needed. This study presents a meta-analysis of greenhouse gases (GHGs) and ammonia (NH3) emissions from four main dairy manure composting methods (static, turning, windrow and silo) based on 41 scientific articles (153 treatments). Gaseous emissions and secondary variables such as average composting temperature, initial moisture content, initial total carbon (TC) and initial total nitrogen (TN) content from each compost treatment were extracted and normalised to enable inter-study comparison. Six mitigation measures for composting were selected and mitigation efficiency (Em) of each measure on different gas emissions were calculated. Gaseous emissions from different composting methods showed large differences. Turning composting resulted in larger carbon and nitrogen losses compared to other composting methods. Although silo composting significantly promoted NH3 emission, it reduced GHG losses by 82.84% compared with turning composting. Principal component analysis showed that the initial TC and TN content of the composted material were crucial in mediating gaseous emissions. Low TC and TN content can simultaneously reduce CH4, CO2 and N2O emissions. Applying compost biofilters was the most effective way to reduce NH3 emission with ME value of −97%. Adding sawdust or straw could reduce CH4 and N2O emissions by 66.3% and 44.0% respectively. Gaseous emissions from dairy manure composting varied a lot and were affected by physical characteristics of composted material and management practices of composting.