Xiaoyan22,a kind of medium gluten wheat,was used to study the effects of different nitrogen topdressing levels on the yield and structure factors and the main biological characteristics in jointing stage and booting stage.The result showed that nitrogen topdressing had effect significantly on yield in the different stages,and the yield increased 11.3% by different treatment.The effect of nitrogen topdressing on yield closely related with the fertilizer time and level of nitrogen fertilizer,and the yields wa...