Use of Manure Treatment and Microbial Processes to Mitigate Gaseous Losses of Nitrous Oxide and Ammonia from Incubated Soil.

Anaerobic digestion of slurries has the potential to mitigate losses of reactive N. A laboratory incubation study was conducted to determine whether application of anaerobically digested slurry and simulated methods of incorporation (subsurface deposition) reduced nitrous oxide (N₂O) rates and ammonia (NH₃) volatilization relative to raw dairy (Bos taurus) slurry or urea. A second objective was to correlate genes that regulate the processes of nitrification and denitrification with rates of N₂O production, slurry treatment and application method. Ammonia volatilization ranged from 14% of the total N applied in raw slurry (21.7 kg NH₃-N ha^-1), to 23% in urea (33.4 kg NH₃-N ha^-1) and was reduced by anaerobic digestion. Conversely, anaerobic digestion increased N₂O production. Cumulative N₂O loss ranged from 5.59 kg N₂O-N ha^-1 for digested, broadcast manure to 0.61 N₂O-N ha^-1 from subsurface deposition of raw dairy slurry. Genes of interest included a 16S rRNA gene selective for ß-subgroup proteobacterial ammonia-oxidizers, amoA , narG, and nosZ  quantified with qPCR and RT-PCR. Anaerobic digestion of slurry increased nitrifier and denitrifier gene copies that correlated with N₂O production. Expression of all genes measured via mRNA levels increased with slurry applications. This study provides new information that links genetic markers in denitrifier and nitrifier populations to N₂O production.