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      Belowground Contributions of Pea and Canola to Soil Nitrogen Pools and Processes

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      ARCAND-DISSERTATION.pdf (10.79Mb)
      Date
      2013-07-04
      Author
      Arcand, Melissa
      Type
      Thesis
      Degree Level
      Doctoral
      Metadata
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      Abstract
      Nitrogen (N) contained in roots and rhizodeposits represents a significant input of crop residue-N into soil that is often unaccounted, despite its contribution to the total N budget and its influence on soil nutrient cycling. Utilizing 15N-labeling methodologies under controlled conditions, the goal of this research was to quantify the input of belowground N (BGN), including rhizodeposits and roots, to soil and to investigate the influence of BGN on soil N cycling processes from the major pulse and oilseed crop grown across the Canadian prairies—namely, field pea and canola, respectively. Using continuous 15N2 labeling, the input of fixed-N to rhizosphere soil from pea plants amounted to less than 2% of the total plant N assimilated via fixation. Nodulation and root 15N enrichment were positively related to rhizosphere 15N enrichment, suggesting that the relatively low input of fixed-N to soil was due to low N fixation in this system. Shoot 15N-labeling techniques enabled a higher 15N enrichment in roots; as a result, rhizodeposition was detected in the rhizosphere as well as the surrounding bulk soil. Rhizodeposition accounted for 7.6 and 67% of plant N and BGN, respectively, in mature pea. Temporal changes in the pattern of rhizodeposition were detected as evidenced by differing 15N enrichment in rhizosphere versus bulk soils. In comparison to pea, a higher proportion of BGN contributed to the total residue-derived N from canola. The higher quantity of N rhizodeposition by canola was related to greater root biomass. However, pea rhizodeposition contributed more to soil inorganic N pools; this was sustained over time, as a higher proportion of pea BGN contributed to the growth of a subsequent wheat crop. In addition, wheat uptake of residue-derived N was twice as much from belowground compared to straw residues. Whereas the abundance of denitrifying bacterial communities in the rhizosphere was uncoupled from rhizodeposition and denitrification enzyme activity (DEA), root-derived 15N correlated with DEA in pea and canola. This research highlights the importance of belowground inputs from differing crop species on N budgets and soil N cycling.
      Degree
      Doctor of Philosophy (Ph.D.)
      Department
      Soil Science
      Program
      Soil Science
      Supervisor
      Farrell, Richard; Knight, J. D.
      Committee
      Walley, Fran; Lemke, Reynald; Bonham-Smith, Peta; Siciliano, Steven; Bedard-Haughn, Angela
      Copyright Date
      June 2013
      URI
      http://hdl.handle.net/10388/ETD-2013-06-1075
      Subject
      Nitrogen
      rhizodeposition
      roots
      canola
      pea
      stable isotopes
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