Optimized nitrogen fertilizer application improves yield, water and nitrogen use efficiencies of winter rapeseed cultivated under continuous ridges with film mulching

The continuous ridges with film mulching (CRFM) cultivation pattern has been rapidly adopted for production of winter rapeseed (Brassica napus L.) in northwest China due to significant improvements in soil moisture, water use efficiency (WUE) and yield. However, in many cases, the crop yield, WUE, and nitrogen (N) use efficiency (NUE) were still very low under CRFM cultivation due to the deficiency of N nutrients. The objective of this study was to investigate the response of winter rapeseed to six N application amounts: 0 (N0), 60 (N60), 120 (N120), 180 (N180), 240 (N240), and 300 (N300) kg N ha−1. Aboveground dry matter and shoot N uptake at flowering and harvest, yield, oil yield, ET, WUEY, and WUEOY were all significantly higher in N180, N240, and N300 than in N0, N60, and N120. Average WUEY, WUEOY, N partial factor productivity and N recovery efficiency did not differ markedly between N180 and N240, but were all significantly higher than in N300. However, average seed yield and oil yield in N240 were 11.9% (427 kg ha−1) and 9.7% (144 kg ha−1) significantly higher than in N180. In addition, seed oil and protein content in N240 did not differ significantly from N180 and N300. These results suggest that the optimal N application amount for winter rapeseed under CRFM cultivation pattern is 240 kg N ha−1. This rate simultaneously improves seed yield, oil yield, WUEY, WUEOY and NUE.