Changes of root morphological,physiological characteristics and yield were studied in five different N application levels with sand culture,using three rape varieties.The results showed that root weight,root volume,root total absorption area,root active absorption area,lateral root number,root length,root vigor and grain yield of the three varieties were increased with the increase of nitrogen(N) application.The relationship between root physiological indexes and grain yield was positive.The contribution of root dry weight,root volume,root to...