Effects of application of nitrogen on seed yield and quality of winter oilseed rape (Brassica napus L.).

To explore the effects of N fertilizer rates on seed yield and quality of winter rapeseed, field experiments were carried out in Wuxue County, Hubei Province during 2019/2020 and 2020/2021 seasons. The experiments were set at five nitrogen application levels of 0, 90, 180, 270, and 360 kg N hm^-2. Rapeseed yield, N concentration, and rapeseed quality indexes were measured at maturity stage. The results showed that N application significantly increased rapeseed yield and N content. Compared with the zero N application, the average yield increase after N application was 1548 kg N hm^-2, and the average yield increase rate was up to 32.9%. Within the range of N application rate of 0--270 kg N hm^-2, rapeseed yield increased significantly with the application of N fertilizer. If N application was continued, rapeseed yield did not change significantly or had a downward trend. N application mainly improved rapeseed yield by increasing the number of pods per plant. N application significantly increased protein content in rapeseed. When the N application rate was 270 kg N hm^-2, the protein content was the highest. N application significantly reduced the seed oil content. For every 100 kg N hm^-2 increase in nitrogen application, the seed oil content decreased by 1.6%. With the increase of N fertilizer application rate, glucosinolate, oleic acid, linolenic acid, erucic acid, and saturated fatty acids (palmitic acid and stearic acid) increased, while linoleic acid decreased in rapeseed. Rapeseed quality decreased as a whole. In conclusion, to pursue high-quality edible oil and take into account rapeseed yield, the application rate of N fertilizer was 180 kg N hm^-2. The optimal application rate of N fertilizer was 270 kg N hm^-2 when rapeseed yield and rapeseed cake were taken into account. [ABSTRACT FROM AUTHOR]