Nitrogen Use Efficiency in Parent vs. Hybrid Canola under Varying Nitrogen Availabilities

Abstract

Improving nitrogen use efficiency (NUE) is essential for sustainable agriculture, especially in high-N-demanding crops such as canola (Brassica napus). While advancements in above-ground agronomic practices have improved NUE, research on soil and below-ground processes are limited. Plant NUE-and its components, N uptake efficiency (NUpE), and N utilization efficiency (NUtE)-can be further improved by exploring crop variety and soil N cycling. Canola parental genotypes (NAM-0 and NAM-17) and hybrids (H151857 and H151816) were grown on a dark brown chernozem in Saskatchewan, Canada. Soil and plant samples were collected at the 5-6 leaf stage and flowering, and seeds were collected at harvest maturity. Soil N cycling varied with phenotypic stage, with higher potential ammonium oxidation rates at the 5-6 leaf stage and higher urease activity at flowering. Seed N uptake was higher under higher urea-N rates, while the converse was true for NUE metrics. Hybrids had higher yield, seed N uptake, NUtE, and NUE, with higher NUE potentially owing to higher NUtE at flowering, which led to higher yield and seed N allocation. Soil N cycling and soil N concentrations correlated for improved canola NUE, revealing below-ground breeding targets. Future studies should consider multiple root characteristics, including rhizosphere microbial N cycling, root exudates, and root system architecture, to determine the below-ground dynamics of plant NUE.

Keywords: N availability; N mineralization; canola; fertilizer rates; nitrogen use efficiency; phenological stage; potential ammonium oxidation rates.

Figure 1

Soil ammonium-N concentration (mg NH₄⁺-N kg⁻¹ soil) and soil nitrate concentration (mg NO₃⁻-N kg⁻¹ soil) over four diverse canola varieties and four varying urea-N treatment rates at two phenological growth stages (5–6 leaf stage and flowering, n = 4).

Figure 2

Potential ammonium oxidase rate (µg NO₂-N g⁻¹ 5 h⁻¹) and urease activity (µg NH₄⁺ g⁻¹ 2 h⁻¹) over four diverse canola varieties and four varying urea-N treatment rates at two phenological growth stages (5–6 leaf stage and flowering, n = 4).

Figure 3

Canola (top) N uptake efficiency and (bottom) N utilization efficiency over four diverse canola varieties and four varying N treatment rates at two phenological growth stages (5–6 leaf stage and flowering, n = 4).

Figure 4

Yield (kg ha⁻¹) and seed N uptake (kg ha⁻¹) over four diverse canola varieties and four varying N treatment rates (n = 4).

Figure 5

Nitrogen use efficiency (NUE) and partial factor productivity over four diverse canola varieties and three varying N treatment rates (n = 4).

Figure 6

Spearman’s rank correlation coefficient (p < 0.05) of Category A variables showing correlation (r) among urea-N rates, days after sowing (DAS), plant biomass, nitrogen uptake efficiency (NUpE), nitrogen utilization efficiency (NUtE), ammonium-N, nitrate-N, ammonium oxidation, urease, plant N content, N uptake, and pH in varying canola varieties. Colours and shapes of ellipses indicate the strength of the correlations, with only significant correlations at a confidence level of 95% depicted. Positive and negative correlations are depicted by the respective direction of each ellipse, and positive correlations are depicted with the colour purple and negative correlations are depicted with the colour orange.

Figure 7

Spearman’s rank correlation coefficient (p < 0.05) of Category B variables showing correlation (r) among urea-N rate, % oil content, nitrogen use efficiency (NUE), thousand-seed weight (TSW), seed yield, seed N, start of flowering (DTF), % protein content, end of flowering (EOF), partial factor productivity, and duration of flowering in varying canola varieties. Colours and shapes of ellipses indicate the strength of the correlations, with only significant correlations at a confidence level of 95% depicted. Positive and negative correlations are depicted by the respective direction of each ellipse, and positive correlations are depicted with the colour purple and negative correlations are depicted with the colour orange.