Soil C, N and Growing Season N2O Emissions from a Typic Cryoboralf As a Function of Long-Term Fertilization History and Crop Rotation.

Results from Long-term Agroecological Experiments (LTAEs) have shown that long-term management (tillage, rotation and nutrient management) has a significant influence on soil properties, soil C and N stocks and cycling, crop yields and crop response to applied fertilizers. This presentation summarizes three growing seasons of N₂O emissions from a Typic Cryoboralf under 2 different rotations and 5 different long-term fertility treatments. Established in 1930, the University of Alberta Breton Classical Plots LTAE consists of a 5-year, cereal-forage rotation (wheat-oats-barley-hay-hay) and a 2-year wheat-fallow subject to 8, long-term fertility treatments. This investigation focused on the control(check), manure, NPKS, NPK(-S), and PKS(-N) fertility treatments in the wheat phase of the 5-year rotation and both phases of the 2-year rotation and results from 2013, 2014 and 2015 growing seasons are presented. Over the three growing seasons, rotation was the most significant factor affecting cumulative growing season N₂O emissions. Emissions from treatments receiving long-term fertilizer and manure N applications were higher in the 5-year rotation even though N application rates were lower than the 2-year rotation (50 and 90 kg N ha^-1, respectively) because of significant organic N input from alfalfa in hay phase over the long-term which is evident in soil total N stocks. With respect to fertility treatments, the most productive (highest wheat yield) treatments (manure and NPKS), showed the highest cumulative growing season emissions (1.2 and 1.0 kg N₂O-N ha^-1, respectively), but the lowest emissions per kg of grain. These results illustrate the importance of interpreting N₂O emissions in the context of N inputs from all sources (fertilizer and crop residues) and that long-term management affects soil properties that influence soil N cycling and N₂O emissions.  Further interpretation of these results will focus on N₂O production mechanisms and implications for management.