Carbon Dynamics across Contrasting Temperate Agroecosystems: Soil Organic Matter Pools, Mycorrhizae, Water Use-efficiency, Methane and Carbon Dioxide Fluxes

• Author / Creator

  Kim, Keunbae

• Perennial grain crops have been proposed as a sustainable alternative to conventional annual grain crops, since they potentially hold multiple desirable features including increased soil C sequestration and biodiversity, mitigation of greenhouse gases (GHGs), and reduction of water loss and others. These attributes are accomplished by their no-tillage management, longer growing season, and pervasive root systems. Nonetheless, the ramifications of implementing novel perennial grain cropping systems to the atmosphere, lithosphere, and biosphere remains elusive. In this research, comprehensive comparisons were made to enhance current understanding of how annual versus perennial grain cropping differ in soil organic matter (SOM) pools, GHGs emissions, and mycorrhizae (i.e., AMF). Five contrasting cropping systems —fallow, annual-grain, biennial-grain, perennial-grain, and perennial-forage — were compared with and without N fertilizer addition. A randomized complete block design consisting of four replicates was initiated at sites located in Edmonton and Breton, Alberta, Canada. In addition to the replicate plots, two adjacent 4-ha fields, including annual vs. perennial grain crops, were set up for eddy covariance measurements at the Breton site. By doing so, it was expected that they address a limitation of the chamber measurements with respect to instantaneous and heterogeneous capture, as well as evapotranspiration (ET) comparison. As a result of SOC fractionation, perennial grain crops increased soil C concentration in both transitory and stable pools compared with annual grain compartments, although overall soil C sequestration occurred as a function of N fertilizer, cropping systems, and underlying soil texture. Moreover, substantial CH4 and CO2 uptake were observed in perennial grain cropping system compared with annual grain crops likely due to a shift to favorable GHGs sink conditions such as aeration-moisture balance, photosynthetic activity, and microbial decomposition. However, overall cumulative ET and associated ecosystem-water use efficiency were similar with between the two cropping systems. Lastly, arbuscular mycorrhizal fungi (AMF) community compositions between annual and perennial grain cropping systems exhibited no significant difference, likely due to the genetic similarity of two crops. In addition, the two contrasting study sites had different patterns of AMF alpha and beta diversity, which may be a result of differing inherent soil properties and management legacy effect across field sites. In sum, AMF communities appear to be impervious to annual vs perennial grain crops, rather their most pronounced difference are field site specific. In sum, my research has been conducted for an overall assessment of whether perennial grain crops play a multifunctional role in agroecosystems toward better sustainability.

• Subjects / Keywords

  • Sustainable agriculture
  • Greenhouse gases
  • Microorganism

• Graduation date

  Spring 2022

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-dsjv-ej67

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.