Characterization of Microbial Communities Associated with Nitrous Oxide Production Following Application of Dairy Manure to a Soil.

The objective of this research was to provide new knowledge linking soil microbial processes with a field scale emissions of a key agricultural greenhouse gas, nitrous oxide (N₂O). In a multiple year field study, best management practices for manure application in dairy productions systems have been evaluated.  Liquid dairy manure (LDM) has been applied yearly since 2011 to hay and corn using contrasting application methods on four 4 ha fields. Two fields were in a corn-soybean rotation and received LDM yearly a rate of 135 kg N ha^-1 either in the fall or spring, and two fields were in hay and received LDM yearly at a rate of 90 kg N ha^-1 either broadcast or injected.  In November 2013 hay was ploughed in, and reseeded in the spring of 2014.  N₂O fluxes were measured from the soil half hourly as atmospheric gas samples using a tunable diode laser trace gas analyzer. Soil samples were collected over the growing season, and around key N₂O flux events.   From the soil samples, DNA was extracted and quantitative PCR was used to enumerate abundance, followed by next-generation sequencing to determine functional gene diversity and composition of nitrifying and denitrifying communities. Daily N₂O fluxes varied between treatments within the year and significant differences were observed between fields with the highest emissions from the corn fields compared to hay fields.  In addition, corn fields receiving manure in the fall had greater emissions than spring manure fields.   All nitrifying and denitrifying genes (amoA, nirS, and nosZ) were successfully quantified and sequenced in both fields throughout the study.  These results contribute to the development of a scientific basis for choosing sustainable best management practices for manure application onto cropping systems that are productive and while minimizing their environmental impact through decreasing their contribution to GHG emissions.