Nitrous Oxide Emissions from Dairy Manure Compost

Abstract

Nitrous oxide (N2O), a strong greenhouse gas, is known to be emitted during the dairy manure composting process, so its emissions should be mitigated. Both pile-turning events and inappropriate use of mature compost containing NOx--N may cause N2O emissions to soar, although using bulking agent appropriately can also reduce them significantly. Isotopomer analysis of emitted N2O suggests that bacterial denitrification is the main process of N2O production just after pile-turning events. Significant NOx--N is accumulated in the pile surface between the pile turnings, and β-proteobacterial ammonia-oxidizing bacteria is seemingly the main contributor to this accumulation. Because the amount of NOx--N accumulated in surface explains the N2O production after mixing, denitrification of this accumulated NOx--N is the main source of significant production just after the turning events. Microbes in the pile core do not contribute to this N2O production significantly, while denitrifiers in the compost surface seem to be the main producer of significant N2O just after the pile-turning events. The bacterial community in the compost surface is always dominated by mesophiles, belonging to phylum Bacteroidetes and Proteobacteria. The future direction and mitigation strategy is discussed in detail based on these recent findings.