Timing and rates of nitrogen fertiliser application on seed yield, quality and nitrogen-use efficiency of canola

Effective management strategies for nitrogen (N) fertiliser are important to ensure optimum seed yields and seed quality of canola (Brassica napus L.) crop production. A field experiment was conducted for 3 years in Ontario, Canada to determine the (i) impact of different rates and timing of application of N fertiliser on canola yield and quality; and (ii) fertiliser-N economy, including agronomic N-use efficiency (aNUE), N-uptake efficiency (NupE), N-utilisation efficiency, partial N balance and N harvest index. Treatments included factorial combinations of six (2011) or eight (2012 and 2013) rates of N as urea (46% N) and timing of application (pre-plant only or preplant plus side-dressed applications at the 6-leaf stage). Side-dressed N application resulted in significant improvements in seed yield and protein concentrations (up to 16%) over equivalent preplant-only applications. The highest seed yield (2700 kg ha–1 in 2011 and 3500 kg ha–1 in 2013) was produced by the treatments including side-dressing: 50 + 50 kg N ha–1 or 50 + 100 kg N ha–1 (preplant + side-dressing). Seed protein concentrations varied from 21% to 23% in 2011 and 2013 and up to 28% in 2012. On average, the sum of protein and oil concentrations was 65–68%. Oil yield increased with increasing N rates in 2011 and 2013, but significant increases were recorded only when N was side-dressed at the 6-leaf stage. Drought conditions in 2012 negated responses to N fertiliser regardless of when it was applied. In general, aNUE and N-utilisation efficiency were decreased with increasing N fertiliser rates, but NupE varied among environments with increasing preplant and side-dressed N application. Side-dressed N applications after preplant application resulted in higher partial N balance, aNUE and/or higher NupE than comparative preplant-only N applications. Overall, side-dressed N application led to improved crop N uptake and better N economy of canola production in eastern Canada.