在有效分蘖临界叶龄期划分苗类,尔后实行分类管理,控旺促壮、促弱升级,是促进麦茬杂交稻大面积平衡高产的有效手段。然而,实践得出:三类苗由于前期基础差,穗数不足,中后期的管理只能起到缓解矛盾、弥补不足的作用,不能治本,其单产比一类苗要低50公斤以上。这说明消灭或减少三类苗是大面积再高产的关键。因此,分析三类苗形成的原因,找出对策具有极其重要的意义。一、三类苗形成原因多年研究得出:有效分蘖临界叶龄期(简称N-n期,下同)的亩茎蘖数与最终成穗数关系密切,基本上能反映出 The classification of seedlings at the critical leaf age of effective tillering is followed by classification management, vigorous growth, weak enhancement, which is an effective means to promote the large-area and high yield of hybrid stubble rice. However, practice shows that the three types of seedlings, due to poor foundation in the early stage and insufficient spikes, can only serve to ease the contradictions and make up for the deficiencies in the middle and late stages of management. This shows that eliminating or reducing the three types of seedlings is the key to re-yielding large areas. Therefore, it is extremely important to analyze the causes of the formation of three types of seedlings and find out the countermeasures. One, three reasons for the formation of seedlings Years of research have drawn: effective tillering critical leaf age (referred to as N-n period, the same below) the number of acres of tillering and the final number of spike is closely related to basically reflect