Evidence for the influence of different dairy practices on seasonal nitrous oxide (N2O) fluxes and fungal and bacterial N2O contributions

Background/Question/Methods and Results/Conclusions

This study compares nitrous oxide (N₂O) fluxes between differently managed temperate dairy farms. N₂O emissions carry serious implications for climate change and agriculture accounts for 70-90% of global anthropogenic emissions.

To examine N₂O fluxes, soil was collected from two dairy farms: an intensive rotational organic system and a conventional confinement and mowing system. Soils were processed and incubated along a range of temperatures and selective inhibitors were used to determine relative fungal and bacterial contributions.

Significantly higher N₂O flux rates were measured at the organic intensive rotational grazing system in comparison to the the conventional confinement system (29.11±21.66 versus 3.20±2.17 ug N₂O g dry soil^-1 d^-1; p = 0.003). Soils treated with bactericide (streptomycin) had the largest mean N₂O flux rate over the 7 day incubation in the conventional system, 7.46±9.18, in comparison to >3.1 in the fungicide (cycloheximide) and non-inhibited treatments. The effect of selective inhibitors at the organic farm was less distinct, and although not significant, bacterial N₂O contributions were higher than fungal N₂O contributions. Though the influence of temperature was not significant, large N₂O fluxes were measured at each farm at cold and freezing temperatures. This study also measured methane (CH4) and carbon dioxide (CO2) fluxes. CH4 flux rates were significanlty higher in the conventional system than the organic system, while there was no significant difference between CO2 flux rates.

From this study, we can provide evidence that N₂O production is influenced by dairy management practices. It was also clear that agricultural management strategy may structure the composition and functional capacity of bacterial and fungal N₂O producers.