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

Abstract

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.