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

Abstract Aims 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 (N 2 O) emissions is not well understood. Methods During three snow-free seasons, N 2 O 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). Results When summed across sites over all three years, cumulative N 2 O emissions were greater for LDM than MIN in annual crops (8.75 ± 1.63 and 5.15 ± 0.96 kg N 2 O-N ha –1 , respectively), but not in perennial grasses (2.95 ± 0.55 and 3.76 ± 0.70 kg N 2 O-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 N 2 O emissions than LDM in annual crops only. During forages post-seeding years, area- and yield-scaled N 2 O emissions induced by LDM and LEG were lower than MIN. Conclusion Our results suggest that for a cool humid climate using LDM or LEG in perennial forages and MIN on annual crops can reduce overall N 2 O emissions, while generating similar or lower yield-scaled emissions.