| In the past half century, N fertilizer application had become an important factor to improve oilseed rape (Brassica napus L) yield. However, the increasing rate of N fertilizer application was far more than that of oilseed rape yield, which decreasing N use efficiency, farmers' economical profit and increasing the risk of no-point agricultural pollution. Therefore, it is imperative to control or reduce N fertilizer applying amounts and improve N use efficiency (NUE) of oilseed rape, and the selecting or breeding of high NUE oilseed rape cultivars has especially become more important. Researches on the NUE of different oilseed rape cultivars (genotypes) and their physiological metabolism differences could provide an important scientific foundation to the selecting or breeding of high NUE oilseed rape varieties and heredity and improving rape nitrogen nutrition characters.Field and greenhouse experiments were carried out at the experimental station of Hunan agricultural university in 2003-2005. Six rape varieties (A1, A2, A3, A4, A5 and A6. provided by Hunan sub-center, national center of oilseed crop improvement research) were cultivated to study difference of NUE under N application conditions and three rape varieties (Al, A2, and A5) selected from six varieties were cultivated to further study their characteristics of N uptake and utilization under different N level conditions. The results are summed as follows:Grain yields of 6 varieties (genotypes) had obvious differences growing under Napplication conditions in 2003-2004. The cluster analysis results indicated that the tested varieties with different NUE could be classified into three categories, i.e. high, middle, and low efficiency category, with 1(A1), 3 (A3, A4, and A6)and 2(A2 and A5) varieties in each category respectively. Al had high NUE, while A2 and A5 had low NUE. In 2004-2005, Al, A2, and A5 were cultivated under N applied or not treatments. The results showed that Al or A2 had high NUE under N application or...
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