Differences of nitrogen use efficiency of rapeseed (Brassica napus L.) genotypes and their relations to agronomic and nitrogen characteristics

A field experiment was conducted to investigate nitrogen use efficiency (NUE) of 50 rapeseed (Brassica napus L.) genotypes at two N rates (N 0 and 180 kg/ha). Differences of agronomic and N characteristics between high and low NUE genotypes were evaluated. The results show that NUEs vary significantly among different genotypes, and the greatest differences of NUE ware 2.5-fold (at N 180 kg/ha) and 1.7-fold (at N 0 kg/ha). Genotypic variances of agronomic and N characteristics are observed, of which first valid branch height has the greatest variance (50%), while the N content of seed has the least variance (about 6%). At both N rates, the No. of seeds per silique, grain yield, ratio of grain yield to shoot biomass, and ratio of grain N uptake to shoot N uptake of the high NUE genotypes are greater than those of the low NUE genotypes, while the first valid branch heights of the high NUE genotypes are significantly lower than those of the low NUE genotypes. There are significant negative correlations between NUE and the N contents of different plant parts, stem and leaf N cumulant, silique husk N cumulant, ratio of stem and leaf N cumulant to shoot N cumulant and ratio of silique husk N cumulant to shoot N cumulant. However, there are no significant differences of shoot biomass and shoot N cumulant between the high NUE genotypes and the low NUE genotypes. Responses of the agronomic and N characteristics to N supply are significantly different between the high NUE genotypes and the low NUE genotypes.