Studies on oilseed yield and nitrogen efficiency in different cultivars of oilseed rape（Brassica napus）

The differences of grain yield, nitrogen absorption amount (NAA), nitrogen response (NR) and nitrogen use efficiency (NUE) among 16 winter cultivars of Brassica napus were systematically studied, and as well as contributions of nitrogen absorption efficiency (NAE) and NUE to the differences of nitrogen efficiency (NE). Results show that the differences of grain yield, NUE and NR among the 16 winter oilseed rape cultivars are significant under the N fertilizer applications, while the differences of NAA among the cultivars are significant without N fertilizer application. The cultivars can be divided into four different types based on the NUE and NR under no nitrogen application: 1) Nitrogen high efficiency--nitrogen high response (NHE-NHR), including Xy1, Xy16, Xy17, Xh19, Xh20 and Xy21；2) Nitrogen low efficiency–nitrogen low response (NLE-NLR), including Xy6, Xy8 and Xy9；3) Nitrogen high efficiency–nitrogen low response (NHE-NLR), including Xy7, Xy12, Xy14, Xy15 and Xy24；and 4) Nitrogen low efficiency–nitrogen high response (NLE-NHR), including Xy11 and Xy13. The variation coefficient (VC) of NUE is higher than that of NAE under the N fertilizer applications. It is also showed that the contribution of NUE to NE is higher than that of NAE in oilseed rape. However, VC of NAE under the N fertilizer applications is higher than that without N fertilizer application, and VC of NUE is in reverse. Therefore, it is indicated that under N-stress condition, the differences of NE are from NUE decreased, and that of NE are from NAE increased.