Canola growth, nitrogen uptake, and yield response to nitrogen application

Canola (Brassica napus) is an oilseed crop with high nitrogen (N) fertilization requirements, and the within-plant distribution of N needs to be quantified in spring-habit commercial hybrids in Western Canada. A two-year study was conducted at three locations across Saskatchewan to characterize growth, N uptake and distribution of two cultivars under five N fertilizer rates (0, 50, 100, 150, and 200 kg N ha-1 ). Plant samples were taken at flowering, early pod fill, late pod fill and maturity and divided into organs (stem, leaf, pods, seeds when appropriate). Measurements included stem length, leaf area, dry matter, and tissue N concentration. Plant dry weight, tissue N concentration, N content and seed yield showed a positive response to N application. Different N fertilizer rates had little effect on the proportion of plant dry weight or the distribution of N within plant organs. At early flowering, half the shoot N was distributed in the leaves and rest in stems. Leaf area peaked at early flowering (~900 cm2 plant-1) and then declined, but plant height continued to increase to late pod-fill. Leaf and stem N was remobilized to developing seeds, showing the significance of this vegetative reserve to produce crops with an average yield of 1960 kg ha-1 containing 74 kg N ha-1 in seed. Hybrid canola had a harvest index of 40%, and placed 75% of its’ shoot N content in seed yield. Any increase in vegetative N reserves, such as leaf and stem, could further improve yield in semi-arid spring canola production.