Interactive effects of crop types and nitrogen sources on N₂O emissions in a cool humid climate

Perennial forages in rotation with annual crops can improve agricultural resilience by increasing soil organic carbon. However, how nitrogen (N) sources interact with rotation diversity to influence soil nitrous oxide (N₂O) emissions is not well understood.

During three snow-free seasons, N₂O emissions, crop yields, and ancillary variables were measured at three experimental sites with contrasting soil textures (silty clay and sandy loam) in eastern Canada. Using a split-plot design, we compared a corn (Zea mays L.)-soybean (Glycine max [L.] Merr.)-corn rotation and a mixed perennial grass sward receiving N via: i) mineral fertilizer (MIN), ii) liquid dairy manure (LDM), and iii) inclusion of alfalfa (Medicago sativa L.) to the perennial forages with no additional N (LEG).

When summed across sites over all three years, cumulative N₂O emissions were greater for LDM than MIN in annual crops (8.75 ± 1.63 and 5.15 ± 0.96 kg N₂O-N ha^–1, respectively), but not in perennial grasses (2.95 ± 0.55 and 3.76 ± 0.70 kg N₂O-N ha^–1, respectively). When comparing N sources within each crop type over the three years, MIN generated greater yields than LDM in annual and perennial crops, but lower yield-scaled N₂O emissions than LDM in annual crops only. During forages post-seeding years, area- and yield-scaled N₂O emissions induced by LDM and LEG were lower than MIN.

Our results suggest that for a cool humid climate using LDM or LEG in perennial forages and MIN on annual crops can reduce overall N₂O emissions, while generating similar or lower yield-scaled emissions.