Assessment of Perennial Cereals in Central Alberta: Environmental Performance and Productivity
Creators: Daly, Erin
Publisher: name: University of Alberta Library
Year: 2023

<p>Despite their paramount importance, modern, high-input agroecosystems used for annual grain production are often characterized as degraded systems with substantial greenhouse gas (GHG) emissions, namely nitrous oxide (N2O), a GHG 273x more potent than carbon dioxide (CO2) on a mass basis. Perennial grain crops represent a novel hybrid between annual grain crops and perennial forage crops and are of great interest due to their purported ability to rectify several environmental challenges while continuing to deliver agricultural products. This body of work aimed to improve our understanding of soil nitrogen (N) cycling and N2O production and release from agroecosystems and investigate the environmental performance and productivity of perennial grain cropping. Chapter 2 of this dissertation is a synthesis paper that establishes the conceptual foundations for the N2O priming effect, defined as the short-term increase or decrease in the rate of soil organic N (SOM-N) mineralization in response to a stimulus, such as the addition of carbon (C) and/or N to the soil. Chapter 3 documents a laboratory incubation conducted to examine the effects of N fertilizer and artificial root exudate (ARE) on N2O priming and changes in N2O production from nitrification and denitrification sources. Additions of ARE or N fertilizer alone caused positive N2O priming; while additions of ARE and urea concurrently resulted in an antagonistic interactive effect that diminished the N2O production derived from SOM-N mineralization (p &lt; 0.05). However, results indicate that the combination of elevated root exudation from a perennial cropping system with N fertilization has the potential to amplify N2O emissions due to increases in both nitrification and denitrification sources. Chapters 4-7 document the results of a multi-year field study conducted at two sites in Central Alberta (Edmonton and Breton). Perennial cereal rye (Secale cereale L. × S. montanum Guss cv. ACE-1) was used as a model perennial grain crop for this research. At both sites, an experimental continuum of perenniality (perennial forage, perennial grain, fall grain, spring grain [or annual grain], and fallow) was established. Chapter 4 investigates the productivity of perennial grain cropping systems. Grain yield of the perennial rye in year one averaged 64% and 51% of the fall and spring rye yields at the Breton and Edmonton sites, respectively. Conversely, perennial rye at both sites yielded substantial aboveground biomass compared to other rye crops over both years. Overall, perennial rye cropping beyond two years faced issues of winter survival and weed competition. In Chapters 5, 6, and 7 the environmental performance of perennial grain cropping was assessed by: (1) evaluating how contrasting cropping systems might differentially alter soil physical and hydraulic properties, (2) measuring growing season N2O emissions from contrasting cropping systems and (3) investigating how GHG emissions and soil organic C stocks respond when perennial crops are transitioned to annual crops after multiple growing seasons. While moderate improvements in soil physical and hydraulic properties manifested under the perennial grain crop at both sites when compared to the annual grain crop, they did not do so to the extent of the perennial forage crop. We attribute this to the inclusion of tap-rooted alfalfa in the perennial forage, and the overarching beneficial influence of root density on soil properties. Further, perennial grain crops reduced cumulative N2O emissions at the Breton site by 60% and 94% in years two and three of the study, respectively (Ps &lt; 0.0001). Correlation analyses for both sites revealed that the average root density was negatively correlated with soil available N (p &lt; 0.05) and cumulative N2O emissions, specifically at the Breton site (p &lt; 0.01), suggesting that the enhanced root density of perennial crops reduced soil N availability, which translated into reduced cumulative N2O emissions. However, when the perennial grain crop was transitioned to an annual crop via tillage, gains in soil C achieved at the Edmonton site during multi-year perennial grain cropping were lost to the atmosphere as CO2. In sum, the environmental performance and agronomic productivity of perennial grain cropping suggest that while these novel systems have the potential to contribute to sustainable agroecosystems, yield reductions, winter mortality, and weed pressure suggest that perennial grain cropping is not yet a feasible option for cold temperate conditions. </p>