Nitrogen efficiency and leaf nitrogen remobilisation of oilseed rape lines and hybrids

Improved nitrogen (N) efficiency of oilseed rape is crucial for reducing environmental N surpluses. In this study, a 2‐year field experiment as well as a hydroponic experiment were performed with four hybrids and their corresponding lines. Seed yield and N efficiency parameters of oilseed rape cultivars grown at low N (0 kg N ha^?1) and high N (150 kg N ha^?1) supply were investigated in the field experiments. Hybrids showed higher seed yield than lines, especially at low N supply, because of a superior N uptake. Moreover, hybrids showed higher N harvest index (NHI) across N rates, which also contributed to higher seed yields. Results from the hydroponic experiment showed significant genotypic variation in leaf N remobilisation efficiency (NRE), but no hybrid‐versus‐line difference was found. Cultivars differed significantly in specific N content in senescent leaves, and leaf NRE was negatively correlated with specific N content in senescent leaves. When linking the hydroponic results with the field results, no relationship was found between leaf NRE and NHI. In conclusion, hybrids were superior to their corresponding lines in N efficiency because of higher N uptake and NHI. The higher NHI was, however, not related to genotypic variation in leaf NRE.