Evaluation of nitrogen use efficiency and contributions of soil-and fertilizer-derived nitrogen uptake in a diverse set of canola lines
McCannell R.M. 2025.
Abstract
Canola is a major field crop in Western Canada, requiring substantial nitrogen (N) fertilization
for optimal yields. However, high application rates of fertilizer N to agricultural soils can lead to
environmental N losses and represent wasted inputs and costs. Improvement of canola N use
efficiency (NUE) can reduce N inputs while satisfying crop N demand minimizing costly N losses.
This thesis evaluated a range of commonly used NUE metrics in a diverse set of canola lines.
Additionally, 15N isotope tracing in microplots was used to understand fertilizer and soil N
contributions to plant N uptake and yield. This research intended to identify specific lines with
superior NUE traits that could support the development of canola varieties with improved NUE.
Plant samples collected throughout the growing season provided insight into understanding plant
N partitioning and final recovery of fertilizer- and soil-derived N.
All site-years, yields and measured NUE indices varied between canola lines. Variation
between canola lines for recovery efficiency of fertilizer (15NRE) added at a rate of 100 kg N ha-1
was observed at Saskatoon-2022 and Saskatoon-2023 at harvest maturity. Few and inconsistent
differences between canola lines were found for total N derived from fertilizer (TNdfF) and total
N derived from the soil (TNdfS) at the Saskatoon sites. However, no significant patterns amongst
canola lines could be discerned, limiting attribution to a specific line. Despite low levels of residual
inorganic soil N and adequate N fertilization, soil N was the primary contributor to canola N uptake
contributing 30-79% of total N in the mature plant. 15N-labelled fertilizer was a small proportion
of total plant N, yet post-harvest soil samples revealed a large portion of unaccounted 15N fertilizer
averaging 61 kg N ha-1 at Outlook-2022, 54 kg N ha-1 at Saskatoon-2022, and 51 kg N ha-1 at
Saskatoon-2023. Our findings showed inefficient use of fertilizer N by all canola lines and the
substantial contributions of soil N to plant N.
