The timing of N application makes a difference in canola seed quality and nitrogen use efficiency. Spring application results in the greatest reduction in oil content (Figure 1). For example, the oil concentration reduced by 10% when N was applied where soil test N in 6-foot was higher than 100 ppm in spring in a field located in intermediate rainfall zone. This was because N was not a limiting factor for reaching its yield potential. The additional available N only increased protein concentration. Oil and protein concentrations are linearly and negatively related (Figure 2). This is due to competition for carbohydrate skeletons during carbohydrate metabolism, therefore, increased N supply enhances the synthesis of proteins at the expense of fatty acid synthesis.

Figure 1. Relationship between seed oil concentration and timing of N application.
Figure 2. Relationship between protein and oil concentrations in winter canola seed.
