Reduced tillage increased growing season N2O emissions from a fine but not a coarse textured soil under the cool, humid climate of eastern Canada

Reduced tillage is often promoted as a method to sequester carbon (C) in soils and thus mitigate climate change. However, in certain conditions reduced tillage may increase soil nitrous oxide (N₂O) fluxes, which may negate any climate gains from the potential storage of C in soil. To investigate how long-term applications of different manures interact with tillage effects on N₂O fluxes during the crop rotation, we established a long-term trial in 2009 in eastern Canada, using two tillage (inversion tillage [IT]; and reduced tillage [RT],) and three fertilizer types (pig slurry, dairy slurry and a 0-N control) arranged in a split-plot design with 3 replications. The experiment was reproduced on two contrasting soil textures (silty clay and sandy loam) located approximately 900 m apart in a wheat-corn-soybean rotation. During 2016 (wheat), 2017 (corn), and 2018 (soybean) we estimated the N₂O fluxes from each plot using manual static chambers for the growing season (April to November). Mean cumulative fluxes for the growing season ranged from 0.8 kg N₂O-N ha⁻¹ for the corn/control/IT to 7.6 kg N₂O-N ha⁻¹ for the wheat/dairy slurry/RT in the silty clay soils and from 0.4 kg N₂O-N ha⁻¹ for the corn/control/IT to 3.0 kg N₂O-N ha⁻¹ in the corn/pig slurry/RT in the sandy loam soils. The RT increased soil N₂O fluxes for both slurry types and the control in the clay soil (mean flux for all fertilizer treatments over both seasons were 5.5 and 2.4 kg N₂O-N ha⁻¹ season⁻¹ for the RT and IT, respectively), likely because the higher water content in the RT caused greater denitrification; while on the sandy loam the N₂O flux was similar between the two tillage systems. Manure type had no measurable effect on the growing season N₂O fluxes in either soil type as both provided sufficient labile N. Application of both slurries however, resulted in greater emissions than the control (P = 0.002). These findings suggest that RT on fine-textured soils in this region may not be an effective strategy to reduce GHG emissions.